By J. ALFRED HALL,
Director of the Pacific Northwest Forest and Range Experiment Station U. S. Forest Service
Fig. 1. Sawmill at Yukon, Vancouver Island
THE forest is a dynamic, aggressive organism. A product of natural forces, if left to itself it reproduces, grows, matures, and dies in its component parts, while the over-all composition remains in balance with soil and climate. In a suitable climate it dominates the earth, potentially the most fruitful of all organic resources in its ability to yield varied goods to intelligent use by man.
The forest is composed of thousands of species of trees and it occupies climatic zones from tropical to subarctic; its character is an infinitely variable thing. From the northern forests, where only a very few species compose the whole, to the lush, dense. tropical rain forests made up of hundreds of kinds of trees, there is a variety of material that can be turned to almost any use.
The use to which the forest is put is almost as varied as its nature, but, broadly, it can be classified in the following categories that have regard for the relations that have existed between man and the forest.
1) Relatively abundant forests, heavy population, and intensive use with close attention to the perpetuation of the forest. Examples are plentiful in northern Europe.2) Relatively meager forests, heavy population, and intensive use with little or no attention to the perpetuation of the forest. Examples are found in Africa and the Near East where continued unwise use has destroyed the forest and the land with it.
3) Abundant forests, relatively light population, and heavy use of the forest, with relatively little attention to its perpetuation. This is a temporary or transition phase, exemplified in North America.
4) Abundant forests, relatively light population, and little use, exemplified in much of the tropics.
The impact of people upon the forest has been most severe in its consequences where the resource was meager, the population heavy, and usage bore no relation to the ability of the forest to maintain itself. It has been least severe where the regenerative capacity of the forest was high and intelligent use of the products of the forest was best integrated with that regenerative capacity. Ways of using forest products changed but little for literally thousands of years, but modern technological practices applied to wood have revolutionized the conception of wood as a raw material. Therefore, with expanding usefulness of wood has come and will come increasing impact of population upon the forest resource. It becomes of the highest importance to examine the probable nature of that impact and to formulate those practices that will lead to perpetuation of the resource while deriving from it the maximum of material benefits.
It is possible to take advantage of the potential vigorous productivity of the forest in new ways, to harness the true growth capacity of forest lands to old and new human needs, and to increase the yield of goods at the same time because intelligent and planned utilization of the forest crop can be a most valuable implement in raising the level of forest productivity.
Influence of the harvest upon forest crop. - Forest crops are uniquely distinguished from most other products of the soil in that the methods used in harvesting, and thus the character of utilization of the crop, go far toward determining the yield and quality of succeeding crops. If annual growth of wood in usable form be taken as a criterion of production, it is apparent that those methods of harvesting that encourage the highest practical rate of growth will be, in the long run, most remunerative and provide most goods.
The effect of cutting or harvesting methods on the subsequent crop may be altered in a desirable direction by removing species not wanted in the ensuing forest, thus encouraging the reproduction and growth of more desirable species. Such operations are possible and are executed in the management of mixed forests always with full regard for those basic silvicultural laws governing the varied and complex processes of reproduction and growth. It cannot be said that the science of silviculture is either adequate or properly covered with research activity, but sufficient basic facts are available to make possible rather efficient management of many forest types. It may be confidently expected that continued research will in good time make available the basic structure of silviculture necessary for such management of all important types.
The character and amount of the harvest is usually of great influence in determining the subsequent rate of growth of the remaining stand and the composition of the new forest. This is especially true in the cutting of virgin forests where most often there is biological balance, death of old trees, regeneration of new ones, a static forest in which little or no net increment of wood takes place. Many times there may even be net loss. Such forests are prey to insects and disease and represent not a productive mechanism but an accumulated reservoir of wood that must be drained before it can be refilled at a more rapid rate. Such a forest should be harvested, but in such a way that new trees and new growth are ensured with a composition of species desirable in the general economy. This can be done. and is being done, but too often desire for immediate returns causes haphazard and destructive cutting that destroys the forest conditions themselves, eliminates existing young trees from which current growth could be expected, and delays for many years the building of a stock of young, vigorously growing trees. This has been the tragedy of too much harvesting of the virgin forest, especially in North America.
Fig. 2. Logs ready for dumping into the quill pond at Grosset, Arkansas
Haphazard selective harvesting of only high quality material over many years has led to the degrading of much originally good forest to types in which there is little left but species and qualities of trees that have not been suitable for conventional use. These conventional uses, clear lumber and pulp, for example, have dictated the harvest but the forest has gradually altered in the direction of little or no yield of commercially useful wood. Clearly this unproductive forest can be made productive and capable of furnishing its potentiality of goods only through reversing this process; low quality wood must be harvested in order to encourage reproduction and growth of good trees.
There is ample opportunity for increasing the efficiency of the harvesting operation itself, both from the point of view of its influence on the forest and of reducing the cost of the operation. Imagination and daring applied to the task of cutting and transporting wood ought to produce mechanisms far in advance of the somewhat cumbersome and highly wasteful tools of today. The same idea applies to traditional methods of lumber manufacture with the huge waste of material involved. When the harvest can be conducted cheaply, with the dual purpose of producing goods and maintaining or enhancing the growth of raw material, and subsequent manufacture is well diversified and integrated with the raw material supply, perpetual forestry becomes a realizable fact.
All these processes, whether applied to virgin or degraded forests, involve the removal of wood from the forest in order to increase the rate of production in future years. Such removal of wood costs money and generally the investment is one of long duration, offering a modest earning rate, but realizable only at a distant date. Private capital has not generally been anxious or willing to embark on such enterprises. Governments have done better and, in several ways. have encouraged and executed those types of long-range management required in the handling of forest properties.
Diversified utilization can encourage good forestry. - But, whether governmental or private properties are involved, there is one inescapable fact: opportunity to convert the harvest to goods at even a modest profit is a prerequisite to the execution of the harvest. Within the term "profit" must be included the idea "social gain," for clearly the establishment of permanent industries and communities upon a forest base represents social "profit" of a high order.
If trees must be cut now at a monetary loss in order to provide a better long-range return on capital, incentive to the type of forestry necessary to high production is lacking. Or, to put the matter more positively, the opportunity of recovering even a small present benefit from improved harvesting seems to offer the strongest encouragement to good harvesting practices.
Such harvesting will yield a wide diversity of kinds and qualities of wood highly variable in adaptability for use. Therefore an important impetus to proper harvesting will be given by developing uses for wood, through wood-using industries that can convert all qualities to useful goods. Such uses already abound, They are being exemplified now in many lands, some highly intensive, some more or less haphazard. Rarely are they well grouped into diversified wood-using enterprises, integrated with the kinds and qualities of wood produced by the forest base, but such grouping and integration can be the base for extensive industrialization.
In a broad way, it can be shown that productive forests, planned, diversified, and integrated wood utilization, and a high standard of living accompany each other. Abundant forest resources alone do nut suffice; it is the degree to which they are managed for the production of a steady flow of goods that can be associated with good living. By contrast, haphazard forest products utilization has in the past been followed by general lowering of living standards. More accurately, it seems probable that proper application of modern technology to the diversified utilization of the forest crop can make heavy and important contributions to expanding world economy and generally sustained improved living.
Versatility of wood. - Although wood has always furnished a large share of the world's requirements in shelter and fuel and has contributed in a myriad of other ways to man's comfort, modern industrial and scientific practices have been slow in their application to wood. This is not surprising. Wood is the oldest raw material of man's use. Customs of long standing and habits of thought have limited its sphere while newer technical developments were applied to varied mineral products. Thus, the age of steel overshadowed the steady, reliable use of wood in old engineering ways with spectacular industrial developments and structural forms impossible for wood in its traditional modes of use.
In the chemical field, organic chemistry grew great and organic chemical manufacturing developed on a coal tar base. Only recently have successful synthetic chemical industries developed on the straight chain aliphatic hydrocarbons of petroleum. Likewise, comparatively recently have industries begun to thrive upon products of fermentation of carbohydrate materials. These new chemical fermentation industries are opening broad new avenues in the mass production of new chemicals based on sugars, and thus far, sugars are exclusively products of the soil. Coal is limited in the kind of chemical goods that can be derived from it. Likewise, petroleum is limited in its character and labors under the added handicap of being limited in its amount. Coal is relatively abundant but not too well distributed and not freely available nor unlimited in quantity.
Wood combines within itself possibilities as a chemical raw material that parallel those of sugars, coal, and oil, and adds other possibilities unique to wood. In addition, it can fill its traditional uses, and expand its usefulness as a standardized, highly developed engineering material.
Importance of wood in world economy. - It is not surprising that some nations blessed with abundant forests have developed high standards of living. Such nations have based their living upon a perpetually renewable material and can live well even after the last drop of oil has been pumped, the last ton of steel fabricated, and the last ton of coal mined. This fact arises from increasing industrialization based on wood.
TABLE 1. - WORLD PRODUCTION OF CERTAIN IMPORTANT MATERIALS
|
Wood |
1,200 million tons |
|
Coal |
1,300 million tons |
|
Petroleum. |
275 million tons |
|
Steel |
135 million tons |
|
Milk |
200 million tons |
|
Potatoes |
250 million tone |
|
Wheat |
150 million tons |
|
Corn |
120 million tone |
|
Sugar |
27 million tons |
|
Meat |
30 million tone |
|
Cotton |
8 million tons |
|
Wool |
2 million tons |
In gross tonnage, only coal is produced in greater volume than wood. If all the foodstuffs in the above table be added together they amount to 777 million tons. However, this table omits a very important product of the soil, grass, which is represented in a secondary way in an undetermined portion of the figures for milk, meat, and wool. There is probably no reasonably accurate way of estimating the magnitude of grass utilization. That it is large may be surmised by putting the figure for meat in terms of grass equivalent. Estimating a use of 20 pounds (approximately 9 kg.) of grass per pound (0.4536 kg.) of meat, 30 million tons of meat would represent 600 million tons of grass. It is probable that the total conversion of grass in one form or another approaches the magnitude of the use of wood. An estimate of the distribution of the world's wood consumption among its more important uses is shown in Table 2.
Most of these uses employ wood as wood for final use. Only a few, paper, rayon, and fiber, and some under "other uses." use wood as an industrial raw material. Even then, 1.2 million tons of fiber are produced annually from wood, a respectable figure against 2 million tons of wool, 8 million tons of cotton, and a comparatively unimportant 60,000 tons of silk. The trend of recent years indicates a vast increase in fiber derived from wood that will come the more rapidly because of great improvement in the quality of fiber from wood that is in the making.
Fig. 3. Sawmill at Paskenta, California
TABLE 2. - WORLD WOOD CONSUMPTION AND TRADE (Million m³)
|
|
Consumption |
Trade |
|
Fuel |
800 |
- |
|
Structural uses (lumber, squared timbers) |
450 |
56.0 |
|
Paper |
100 |
60.1 |
|
Rayon and staple fiber |
5 |
60.1 |
|
Railway ties |
30 |
2.5 |
|
Mine props |
30 |
6.6 |
|
Other uses |
85 |
1.4 |
Wood as fuel. - The largest use of wood, fuel, is the most primitive, the most wasteful, and among the most important. Over vast regions, where coal is either unavailable or costly, wood constitutes the only fuel and makes life possible. Even in regions of wood scarcity the population depends upon wood or charcoal for winter warmth and the preparation of food. Indeed, there are many examples of complete denudation of forested lands in Africa and Asia through generations of harvesting for fuel alone.
Pressing as is the use of wood for fuel, its use thus is a wasteful business. In the manufacture of charcoal, a fifth of the weight of the wood is lost as gases and only at best a third of its weight recovered as charcoal fuel. If wood distillation for charcoal is carried out in modern equipment and the by-products recovered, the process is more efficient but still a wasteful conversion of potentially valuable material.
The relative efficiency of heat recovery in the various methods of burning wood fuel might be listed thus:
1) Open fire (lowest)
2) Crude open fireplaces
3) Fireplace with gas circulating accessories
4) Ordinary stove with controlled drafts
5) Highly developed stove and furnace
Fortunately, wood serves well in any of the listed wood-burning equipment, from the open fire at the squatting place of the aborigine, to the automatic, continous feed, gas-consuming furnace of the most highly industrialized community. It is to be expected that the development of industrial uses for wood will tend to decrease its wasteful use for fuel and increase more efficient consumption.
Wood as structural material. - The use of wood for structural purposes is second in importance but it can hardly be expected that any statistical statement could include all the myriad forms that such use takes. In the rude "jacal" of the Mexican Indian, the kraal of the African, the elaborate city home of the Swede, in factory, bridge, and boat, wood has played a leading role. It has carried loads, transported foods, framed and sheathed buildings, and sheltered the builder. It carries the millions of miles of communication and electric wires and supports the wharves that charge and discharge ocean-borne commerce. All these functions and more are fulfilled by wood, as a crude material, for the most part crudely and lavishly used.
In general, the use of wood for structural purposes has until recently been wasteful, due largely to the fact that standard factors of strength and working stresses have been either available or, when available, unapplied. This has led to the use of larger members than were required to carry a specific load, over-design for strength and stiffness, or, more generally, practically no engineering design at all but a mere use of wood as the most easily available material and one that would do the job. Fortunately, the sheer versatility, workability, and relative abundance of wood in many countries have combined to make it the universally used housing material that it is.
The use of wood as railway ties, while relatively small in volume, is of tremendous importance. It is hard to conceive of the railway transportation systems having reached into all corners of the globe except upon a wood base. Only where wood was very scarce and expensive have other materials replaced it for sleepers and nowhere are other materials used by preference.
Similar remarks apply to the use of wood in the mines. Perhaps other materials could be used for the job, but this rarely occurs.
This age-old engineering material, wood, has thus delivered immeasurably valuable service to man and continues to do so. However, from two points of view, the uses of wood are changing rapidly and will probably continue to change. First, new advances in general fields of technology have application to the manner in which wood is used. In general, they have the effect of broadening the scope of quality of wood that can be used for a specific purpose. Second, the use of wood and, thus, the harvesting methods have become a most important tool with which to control and perpetuate the resource itself.
Lumber - improvements in manufacture and application. - There seems to be no question that, generally, wood for structural material will continue to be the most important single product of the forest as far as value is concerned. While it is true that in Canada and Scandinavia short forest rotations are being planned on au exclusive pulpwood basis',. possibilities of such operations have definite economic limits. In most forest territory, lumber is the primary product; it must bear the major cost of forest management, of sawlog transportation, and primary manufacture.
In the past, with the exceptions noted, the lumber market has pretty well determined silvicultural practices. Thus, although no particular broad effort has been made to grow high quality lumber outside of Europe, the demand for such lumber and the prices brought by it have caused selective harvesting and culling to the eventual detriment of the productive capacity of the forest. The growth of lumber has been left too much to chance in most of the world. The essential problem in lumber is twofold: the application of modern technology to the broadening of the supply base, including species and qualities of trees not hitherto harvested for lumber; and maintaining and increasing consumer satisfaction in lumber even while broadening the base.
Forests do not grow all clear lumber. There are trees and parts of trees that can make only knotty lumber or can produce only short lengths of clear wood. The ideal forest management occurs when the harvest can take the whole growth in a balanced way, and use can be found in the whole crop. This ideal can rarely be reached, but diversification of the lumber harvest itself can go far toward its realization.
The waste of wood involved in growing, harvesting, and manufacturing lumber is truly appalling. When unused species and cull trees left in the forest; tops, limbs and breakage left in the harvest; and slabs, edgings, sawdust, and trimmings in lumber manufacture are all added together, less than one-third of the total volume of wood grown in the forest gets to market. The waste of material in production of pulp is not much different. It is upon this present waste pile that future conversion industries can be based, with resultant benefit to the forest in addition to increased production of useful goods.
Techniques of lumber manufacture and use are far advanced today compared with their status fifty years ago. Widespread use of controlled drying machinery has brought about orderly marketing of lumber. dried to specified moisture content for specific uses. Air-drying procedures, useful in some climates, are better controlled. And both methods yield lumber today that approaches standardized quality. New techniques of seasoning that make use of chemicals are being applied to many species that have been classed refractory, unsuited for lumber manufacture. The same techniques are being applied to the seasoning of heavy timbers, with large reduction in degrade and corresponding increases in consumer satisfaction.
There is room for great improvement in international trade practices in the fields of lumber grade and moisture content standardization. Uniform and satisfactory grades and standards for lumber of whatever origin should go far toward eliminating existing prejudices and difficulties in marketing. Likewise, uniform international standards of strength are needed in order that lumber specifications may be internationally applicable.
An interesting new development in seasoning practices is represented in the use of solvents to remove water. There have been numerous approaches to this problem in the past. generally unsuccessful. It now appears that commercial application of certain new principles may be practical in such a way that the extractive materials dissolved from the wood by the solvent go far toward paying the cost of the process, while a higher grade lumber is being produced. Preliminary indications are that the process may have rather wide applicability especially to certain hardwoods notoriously difficult to dry. By-products will vary from species to species, but oils. fats, resins, and certain sugars may be expected to be produced.
Rapid drying procedures are being developed that depend upon the generation of heat inside the wood by high-frequency electric currents. Where very cheap electric power is available, this field may become important.
Improved durability. - Wet wood decays more rapidly than dry wood - a very good reason for seasoning wood. But in many uses wood must be wet and still able to resist the action of decay organisms. Some woods are very durable under damp conditions, but the most abundant ones are not. Therefore, they are impregnated with toxic chemicals that render them more or less immune to attack by fungi and insects.
The oldest and still most widely used preservative is coal tar creosote which is reasonably economical and quite effective. For example, properly creosoted railway ties now last 30-40 years, whereas 10 years is considered a good life term for uncreosoted ties. Proper treatment, applied to timbers, posts, piling, and supports that must be installed in damp conditions ensures a long life.
However, for many uses where durability is required creosote is unsatisfactory because of odor, color, and general smeariness. More satisfactory treatments have been devised using various chemicals that leave the wood clean, odorless, and capable of being painted. It may be confidently expected that, as chemical science progresses, new chemical combinations will be developed that will be better than those already in wide use. There is also promise that a generalized theory of toxicity of organic compounds will lead to the synthesis of materials specifically designed for wood protection. In short, although the task of protecting wood against insects and decay has been well done, larger improvements may still be expected, both in quality of service and cheaper treatments.
Fireproofing. - Wood is combustible and, in dense centers of population, has lost much of its inherent advantage as a structural material because of this property. Modern techniques of impregnating wood with fireproofing chemicals have created substantially fireproof wood. The processes are still costly, however, and cannot produce cheap fireproofed wood for general use. They can and do make available fireproof wood for use in critical situations or points of high fire danger.
Strangely, although wood and other materials are fireproofed, successful treatments have been mostly accomplished by empirical experimentation. No satisfactory theoretical explanation of the ability of certain chemicals to prevent combustion has vet been developed. Undoubtedly this will be done and when accomplished, will lead to a sure scientific basis for fireproofing. In the meantime, lumber can be fireproofed. and certain forms of modified wood to be described later, are substantially fire resistant.
Prevention of shrinking and swelling. - Although a considerable degree of stability is imparted to wood by proper drying, insofar as taking on and giving off moisture is concerned, generally it still shrinks and swells as relatively humidity changes. This property varies widely among species and within species according to growth rate and other variables. This may lead to warping, cupping, or splitting of wood, and various other manifestations that militate against fully satisfactory use. An important new development bids fair to furnish a cheap and satisfactory means of greatly reducing this tendency. Fortunately, the treatment is simple - merely heating the wood to rather high temperatures short of charring, under determined conditions of moisture content. Under these conditions, reductions of 40 percent in shrinking and swelling are obtained, which greatly improves the serviceability of wood for many purposes.
Laminated timbers. - These treatments designed to improve the serviceability of wood are generally applicable to lumber and timbers, but the task of utilizing the entire forest crop calls for means that will use short pieces - and small pieces that may be cut from boards of such low grade as to be unsalable as lumber. A great impetus has been given this field by the gradual exhaustion of virgin timber capable of yielding large members, and the necessity for replacing these large members by built-up pieces. The field itself is capable of exercising much influence on harvesting practices by permitting the profitable cutting of low-grade trees and recovery of their lumber yield in small pieces.
It should be pointed out that the development of techniques for laminating boards, and gluing of small pieces or gluing them by scarf joints, continuous edge gluing and the like, is comparatively recent, and is expanding rapidly as new and more satisfactory glues and gluing methods are available.
There are actually distinct advantages in built-up members over sawn timbers. Boards can be satisfactorily and thoroughly seasoned with less damage than can timbers. Hence, the gluing-up process offers a ready means of producing large preseasoned timbers that are stable and free from defect. This distinctly sharpens engineering design because the properties of the fabricated piece can be more accurately known and, in fact, these heavy pieces can be "tailor made" for particular jobs.
The construction of laminated arches from wood derives simply from the construction of laminated timbers. The flexibility of single boards, either sawn whole or built up, permits them to be bent successively and clamped to a form as a glued assembly. As the glue sets, the boards are firmly joined in a unit, the size and form of which can be predetermined and carefully engineered for the specific function.
The easy workability of wood, the comparatively small investments required for fabricating equipment, and especially the adaptability and utility of the fabricated material make lamination of timbers, arches, trusses, and other structural units a promising outlet for a great deal of material not hitherto usable as lumber. The introduction of thermosetting waterproof resin glues, combined with new methods of applying heat rapidly and economically to the glued joint, make possible laminated materials suitable for exterior use or for such trying uses as boat keels and ribs, large numbers of which have been manufactured during the war. The next great improvements may be expected in the production of quick-setting cold resin glues that will be waterproof, thus eliminating the necessity for heat in joining and greatly cheapening the process.
Durable plywood. - The new waterproof resin glues have also revolutionized the plywood industry, turning it from the manufacture of a material strictly for interior or temporary use to the manufacture of a thoroughly weather-resistant material of well nigh universal applicability. Weatherproof plywood, glued to supporting members, contributes a large share of strength and stiffness to the unit. Such units are so strong that weight can be reduced to a minimum and they can be fashioned easily in mass production for specific purposes. This has brought about the use of plywood as a construction material par excellence, and its use in this field is rapidly expanding.
Supplies of veneer-quality timber are limited in the Northern Hemisphere, especially as regards the clear, virgin softwoods that are contributing too heavily to the volume of cheap plywood being manufactured. Trends may be expected in the following directions: 1) pruning for the production of veneer logs; 2) new methods of producing satisfactory veneer from small logs; 3) utilization of tropical hardwoods for plywood.
Techniques for bending and molding plywood are well developed so that an enormous variety of forms and shapes can be easily produced. Also, the use of new special wood and paper products as well as metals for facing plywood may be expected to give a large variety of new and serviceable materials based on veneer and resin glues.
Wood a standardized engineering material. - These new forms of fabricated wood, capable of accurate engineering design and with accurately predictable properties, are rapidly lifting wood to the level of a standardized and preferred engineering material. A very old handicap under which wood suffered in heavy construction, the difficulty of joining large timbers as a strong joint, has been overcome in recent years by the development of a large number of special connectors made of metal. With these connectors a wide variety of joints can be satisfactorily built, the wood being factory machined for the connectors, and assembly taking place on the job. Large trusses and trussed arches are being erected with entire satisfaction and distinct advantages in many applications. The system lends itself well, also, to prefabrication of smaller members for assembly into structures at the building site.
The trends in fabrication and in joining wood have been combined with intensive research in the mechanical properties of wood to change its status radically within the past 25 years. It takes its place now as a precision engineering material with inherent natural advantages that ensure its permanent status. Continued research in new methods of use and further refining of its engineering properties should further raise its level of adaptability.
Most of these newer trends in wood utilization require, or will be better met by, wood of good quality, clear lumber, or lumber of comparatively high grade. Veneer manufacture requires clear wood for good yield and efficiency. The engineering advantages of wood are functions of its own peculiar structure and clear, straight grained wood apparently will always command a premium.
New industries from waste. - It must be repeated, however, that the process of growing such wood is almost always accompanied by the growing of variable proportions of lower grade trees; tops and limbs must be produced, and lumber manufacture inevitably produces a good proportion of offal. There is a school of thought that looks at the forest as merely a future producer of wood to be ground up, pressed into "synthetic lumber " or plastics to the final exclusion of structural material as a principal product. There is nothing yet technically possible that warrants such a point of view. Disintegrated wood, reassembled in any form, lacks the strength and the oriented strength of normal wood and is not as adaptable or workable in the myriad uses of wood.
The costs of so-called "synthetic boards" are mostly manufacturing costs and they can return little for the cost of growing trees. Forestry will, in all probability, continue to receive the major share of its returns from good lumber and veneer, posts, piling, and the like. While industries may be based on the byproduct wood, the price of the raw material for these industries must in all probability be low in order that the industries may survive.
"Impreg" and "compreg". - The inherent valuable properties of natural wood, its high strength-weight ratio, great strength along the grain, resilience, and ease of fabrication, have been vitiated to some extent by its tendency to shrink and swell under variable moisture conditions. The ideal material for most uses might be visualized as combining high thermal stability and imperviousness to moisture with the strength of steel, the hardness of diamond, and ease of working. There has never been any such material. Most materials are lacking in some property and those combining most desirable properties are rare and expensive.
For generations efforts have been directed toward developing in wood those properties it lacked while preserving its inherent advantages. Obviously, because of the abundance of wood and its broad distribution, the accomplishment of this task in an economical manner would be expected to broaden its applicability in those fields now occupied by it, and to render it serviceable in fields for which it has not been suitable.
In recent years most attention has been given to overcoming or reducing the property of wood to take on and give off water as relative humidity changes. Doubtless, this is the most troublesome property of wood and one that is widely variable among species, within a single species, and even with a single piece of wood. The peculiar structure of a log, the way a tree grows, is responsible for the fact that the greatest shrinking and swelling takes place in a direction tangential to the original round log, the next greatest in a direction radial in the original log, and least of all longitudinally. These facts introduce many complicating factors in sawing lumber, kiln drying or air-seasoning, grading, selection for use, and fabrication. Lack of dimensional stability under changing moisture conditions is probably the most undesirable property of wood.
The wood fiber itself is a hygroscopic material, that is, it has a great affinity for water. The cellulose component of the fiber has tremendous affinity for water and responds rapidly to even relatively minor moisture changes, altering the size and shape of the fiber and thus the piece of wood itself.
Two fields of purely fundamental research have contributed heavily to advances toward solution of the problem thus posed. Primarily, the knowledge of the ultimate chemical composition of wood developed during the past 50 years has brought about excellent understanding of the chemical groupings responsible for the properties of the internal surfaces of wood. Secondarily, but of tremendous importance, the newer field of surface or colloid chemistry has given understanding of the physical nature of the relationships existing between internal wood surfaces and liquids, especially water.
If it be considered that the submicroscopic internal surface existing in a cubic inch (16 cm³) of wood amounts to about an acre and a half (6,000 m²) and that all this surface is capable of physically binding a layer of water several molecules in thickness, the complexity of the problem becomes evident. Most of the swelling that takes place when wood absorbs water is internal, but the net result in changed external dimensions is the more disturbing.
Fig. 4. Selective cutting in Ponderosa pine, Pinus ponderosa Laws, stand in Oregon
"Impreg". - At first glance, the obvious solution is merely to plug the very small pores and open spaces in wood with materials that are not wetted by water. This has been accomplished by the use of waxy and paraffin-like materials applied in various ways, either impregnated in molten condition under pressure or impregnated under pressure or by diffusion while in solution in an appropriate solvent, later evaporated. The net result is always about the same. A slowing down of the rate of swelling is obtained, but the final product is the same as though no water-resistant impregnant were present.
This result has been shown to arise from two facts: the impregnating substances, being always large molecules, could not possibly enter the submicroscopic spaces between the "fibrils" or very small particles of cellulose composing wood fiber; and the chemical nature of the internal surfaces, their affinity for water, was not altered by the treatments. The action of the impregnants was a purely physical one, slowing but not stopping the absorption of water.
Considerable advancement in this field became possible with the development of synthetic resins of the phenol-formaldehyde or "Bakelite" type. The components of the resin, phenol and formaldehyde, small molecules, are introduced into the wood in solution and then formed into resin by heating the impregnated wood. The small size of the molecules permits complete permeation of the wood structure and the chemicals themselves react with the wood internal surfaces, thus decreasing their affinity for water. Using this process, the swelling and shrinking of wood is reduced to 30 percent of normal with improvement in compressive strength and hardness but lowered resistance to impact. Electrical resistance is increased because the wood remains drier under all conditions. Resistance to decay and termites is greatly enhanced.
In general, the applicability of the process is limited to woods that are readily permeable to liquids and the cost is considerable because of the relatively high cost of the resin-forming components employed. The broadly increasing uses of such resins are causing, intensive search for cheaper ones, a source for which may well be within the wood itself. The process has been much used in Europe and may be expected to become more widely employed.
"Compreg". - A modification or extension of the impregnation process just described yields a product with vastly improved properties. Impregnation is carried out as above, the objective being to complete penetration of the wood substance with the resin-forming chemicals and also chemical reaction with the water binding elements of the internal cell wall surfaces. This latter, accomplished by heat, is accompanied by plasticizing of the wood which makes it compressible under pressures of 1,000 pounds per square inch (70.3 kg. per cm²). Under these conditions, almost any species of wood can be compressed to a specific gravity of 1.3 to 1.4 and about one-third its original thickness. Practically all the softer woods can be compressed to half their original thickness by pressures as low as 250 pounds per square inch (17.6 kg. per cm²). This makes possible the compression of face veneers and their simultaneous assembly with untreated slices, or with treated and pre-treated cores with but slight compression of the cores. Such products will have the desirable surface properties of "compreg," the common designation of the product, combined with lightness and cheapness in the more bulky core.
"Compreg" takes a high degree of polish and, because it is the same material throughout, scratches or scars can be easily removed by merely sanding or buffing.
Water absorption by "compreg" is so low as to be negligible for practically all uses and its dimensional stability is all that could be desired. Its strength is proportional to the degree to which it is compressed; if to a third of its original volume, general strength properties are trebled and approach those of a mild steel. Strength-weight ratios are of the order of light metal alloys. Brittleness is again increased, a property not particularly important in the uses to which the material will be put.
This new, strong, durable, and stable material can be machined easily with metal-working tools. Therefore, techniques have been developed in which the final object of manufacture is roughed out with woodworking tools before compression and is then formed in a mold under appropriate pressure. Wood, therefore, becomes a molding plastic in a way, but its inherent valuable oriented strength properties are preserved.
It is of great importance that satisfactory "compreg" can be made from woods of any original density, very light or very heavy. Only highly resinous woods and woods relatively impermeable to liquids are excluded.
"Uralloy". - Other materials than phenol-formaldehyde resins are available with which to improve wood properties but, to date, none have shown equal properties. Some are more economical, for example, the urea-formaldehyde treatments, but do not yield as good a product. The field of other impregnants is being diligently explored and, doubtless. the chemist will turn up better materials. It is even probable that lignin, itself derived from wood, may become the source of improved resins for impregnation since recent work shows it to be a good source of certain resin-forming chemicals.
"Staypak". - The cheapest method of increasing the strength and dimensional stability of weak woods of low density appears to be one that takes advantage of the fact that wood is plastic to some degree and compressible when heated to moderately high temperatures under a certain controlled moisture content. The process is said to be rapid and economical, consisting of merely heating the piece to proper temperature and compressing to the desired density. Strength of the compressed wood is generally proportional to the density, and ultimate shrinking and swelling are about the same as that for a piece of wood of the same size, but the rate is very greatly decreased. This fact makes the product suitable for many uses where humidity is variable but resistance to immersion in water is not necessary.
All these new processes seem to offer opportunities for the utilization of tropical species whose properties are such that they have not hitherto entered world markets.
It has long been apparent that the permeability of wood to gases offers an excellent opportunity of obtaining quick and complete penetration with reactive materials. Unfortunately, few of the materials hitherto found most useful are vapors at satisfactorily low temperatures. Progress is being made, however. and recent successful treatment of wood with vapors of acetic anhydride to block the chemical groups that are responsible for water absorption has shown promise.
In short, it appears that considerable progress has been made in modifying wood to eliminate or reduce one of its least desirable properties, shrinking and swelling, while enhancing its beauty and durability. The field is a young one, susceptible to much more productive exploration, and one that will have to be re-explored as progress is made in chemical fields that develop new impregnating materials.
When wood is used in its original form or as some form of impregnated and compressed wood, its value rests upon its physical and mechanical properties. But this versatile material is also an interesting and important source of chemical goods and must therefore be regarded as a raw material of chemical engineering.
Destructive distillation of wood. - Certainly the oldest and probably the most widespread use of wood as a crude material for chemical engineering is the process of dry distillation, principally for the manufacture of charcoal. The world over, transformation of bulky wood to light-weight charcoal, concentrating fuel value in relatively pure carbon, has been a principal source of domestic fuel. Since charcoal is easy to transport and burns with an easily controllable, practically smokeless fire, its use is well nigh universal, especially in those countries not possessed of developed coal or oil supplies that have been made available for domestic consumption. A prime advantage of charcoal as fuel has been the primitive nature of the arrangements necessary for its use. The simplest brazier of charcoal may suffice to cook a meal or warm the interior of a hut when no other heating apparatus is possible.
Thus, from earliest times, charcoal burning has been a well developed art and has followed man whenever he has had forests. Charcoal has been the basis for domestic heat, but it has also contributed to the advanced use of metals. Just when and where iron was first separated from its ores by the use of charcoal is lost in the dim past. but the production of the highest qualities of steel for special uses and nonferrous alloys of specified carbon content and purity still depend to a large extent upon charcoal. In many countries of high population density in proportion to forest wealth and low industrialization, the continued impact of charcoal burning upon the limited forest has reduced the forest to a very low level of productivity. In other countries that are relatively rich in forests and well industrialized, charcoal manufacture, or rather wood distillation, has been a good tool of forest management, since the industry can and does use tops and limbs as well as low-grade cull wood. There is no question that, if the economic situation is satisfactory, wood distillation is an attractive component of a balanced scheme of forest products utilization.
In general, distillation for the production of charcoal alone takes place only under two sets of conditions: 1) limited fuel supplies and demands, thus a semitropical climate with a low industrial development; 2) production of charcoal for industrial or domestic use on a highly developed technical scale with full recovery of distillation by-products.
In the first case, distillation is a crude business, carried out by piling wood under turf or mud in such a way as to burn it with limited access of air, allowing the products of distillation to escape as part of the smoke.
In the second case, distillation is accomplished in closed retorts connected with condensing and refining apparatus to recover the valuable chemicals contained in the distillate. These are combustible gases, methanol (wood alcohol), acetic acid, and tars, along with minor constituents over one hundred in number. Since most of the tar components occur in very small percentages, their separation on a commercial scale has rarely been attempted. The gases are generally used in heating the wood. Formerly, the commercial demand for methanol and acetic acid, either for use as such or for manufacture of acetone, was an important factor in maintaining a vigorous wood distillation industry, especially in Europe and America. More modern and cheaper processes for the production of synthetic methanol and acetic acid, as well as acetone and acetic acid by fermentation, have thrown the burden of costs upon charcoal alone. Thus, only a few of those plants best equipped for complete recovery and with cheap and abundant wood supplies have been able to maintain themselves.
From a strictly scientific point of view, wood distillation is a wasteful procedure. Roughly, the final yield from hardwoods consists of about 38 percent charcoal, 42 percent volatile condensible material, and 20 percent gases where the distillation is the ordinary technical type. From softwoods containing resins, yields are different and other products of turpentine character are obtained. Clearly only the most efficient recovery and use of the condensate can be profitable in a highly industrial economy. Charcoal must compete with cheaper sources of industrial carbon in metallurgy and command a premium only where purity is a requisite or where high gas absorptive capacity is necessary. Both fields are limited in the tonnage they can normally absorb.
Having regard for the potential values in wood that can be obtained by more refined chemical procedures, it does not seem likely that the dry distillation of wood as now carried out, can long persist as a part of industrial wood technology except under most favorable conditions of wood supply and market for charcoal. No heavy expansion of the existing industry can be foreseen. However, it should be pointed out that research could very easily bring about a major transformation in this old industry and put it back on a computing basis.
It has been found, for example, that vacuum distillation yields products of entirely different nature that have not yet been subjected to critical examination. Furthermore, distillation under the influence of various catalysts offers a field of exploration that is attractive, especially when combined with high-frequency radio heating so as to achieve closer thermal control during distillation. It is to be hoped that such improvements will be forthcoming as will make wood distillation economically possible because no other process can yet absorb such a wide range of species and qualities of wood.
Pulp and paper. - The manufacture of wood pulp and paper products in contrast with wood distillation for charcoal manufacture, is comparatively limited in its extent to industrialized countries. It is further limited in the nature of the woods that it can utilize but, in countries with large sources of suitable wood and good paper markets, it has become an important economic factor.
It is the base for most paper, thousands of products of everyday use from pulp or paper, and a rapidly growing textile and fiber industry. It furnishes the raw material for the many new chemical industries developing around wood cellulose as a raw material. It has grown by leaps and bounds in the last 25 years and, as new industrial uses for paper appear, seems to have no visible limit of magnitude. While only 22 percent as much is now used for paper as for structural purposes, 60 percent of the product enters international trade. If a nation's use of paper may be taken as a rough measure of its standard of living, the world will need enormously increased volumes of wood pulp products, as general living standards improve. These must come from the forests, and the forests must increase in their capacity to satisfy world demands.
Perhaps because most present wood pulping processes were developed in predominantly coniferous regions, they have been best adapted to coniferous trees. Roughly, the principal pulping processes are: 1) acid processes, exemplified by the sulphite process, principally applied to spruces, firs, and hemlocks; 2) alkaline processes, exemplified by the "Kraft" or sulphate process, principally applied hitherto to the pines; also the "soda" process, applicable to hardwoods; 3) the "semichemical" process, originally applied to hardwoods but apparently quite broadly applicable; and 4) the mechanical or "groundwood" process, generally applied to soft woods of light color.
Acid and alkaline processes have in common the feet that they are intended to dissolve the lignin component of wood while leaving the cellulose in a more or less purified condition in the form of a fiber. They are applied under widely variable conditions in accordance with the desire to produce wood pulps that can meet an enormous variety of requirements. These may cover the entire range from nearly pure alphacellulose for rayon manufacture, to a crude, unbleached pulp for manufacture of a fiber board, from a high-grade "bond" paper to a coarse "butcher's wrapper. " Strength requirements are as widely variable. There occurs, therefore, a highly complex interplay of wood species; pulping methods, and paper-making technology in the production of the enormous variety of pulp and paper products.
The development of the two other processes, semichemical and groundwood, arose primarily from the cost and low yield of the chemical process. Generally, the chemical processes yield 50 percent or less of the weight of the wood as pulp.
Since the cellulose and hemicellulose fractions together make up about 75 percent of the wood fiber, it seemed logical to preserve the fiber structure by disintegrating the wood by less violent means than usually employed. In the semichemical processes this is accomplished by mildly cooking wood chips in an appropriate softening medium and then breaking the chips into fibers by mechanical means. In the straight mechanical processes, the billets of wood are held against rapidly revolving stones and are literally eroded into fibers. Both processes give high yields of pulp suitable for many purposes where best color and high strength are not required.
The semichemical processes in particular are capable of much wider application on a broader base of wood species and quality. These processes, in some forms, use spent liquor from sulphite or sulphate mills as softening agents and are thus admirably suited for incorporation into diversified utilization organizations. Since they are generally much less critical of wood species and quality than the strictly chemical processes, they can employ woods and sawmill waste, the refuse from lumber and chemical pulp manufacture.
The mild chemical action to which semichemical pulps have been subjected results in the presence of a high percentage of pure alphacellulose that would be degraded by the more severe treatment of the standard chemical methods. Processes have been designed to remove the hemicelluloses and traces of lignin from these pulps, with the production of remarkably high yields of alphacellulose in forms suitable for textile or sheet viscose manufacture, or incorporation into a broad and increasing variety of cellulose plastics. High-grade cellulose for chemical manufacture, derived from these processes, may be expected to compete favorably with similar products based on chemical wood pulp or cotton.
The acid or sulphite pulp process has generally been applied to woods with long, strong fibers and light color, or easily bleached. Since good penetration of an acid cooking liquor into the chips is absolutely necessary; pitchy or knotty wood cannot be used. Hardwoods have not given good results, nor have any but young pines containing little or no heartwood been usable. In some countries, a system of forestry is possible that aims at the continuous production of wood suitable for sulphite pulp and the integration of sawmills with such production. Sulphite pulp is generally light in color and strong, therefore useful in combination with short-fibered pulps. Need for it will probably continue, but a shrinkage of the industry in North America is anticipated as the supply of sulphite wood lessens.
This lost volume of sulphite pulp will be more than compensated by expansion of the sulphate pulping industry, based on new procedures that not only make the process applicable to many previously unused hardwoods; these new procedures can even pulp mixtures of hard and softwoods and are beginning to approach the time when " run-of-the-woods " billets can be pulped satisfactorily without regard for species.
A radically new pulping procedure developed in the United States of America gives promise both of increased yields of pulp and new industries based on wood. The process, called the "holocellulose process," effects a clean separation between the lignin and the carbohydrate components by very mild procedure. The carbohydrate mixture, about two-thirds cellulose and one-third hemicellulose, may be used as pulp or further fractionated for the separation of the hemicellulose fraction and the production of high purity chemical cellulose. These hemicelluloses offer industrial possibilities along many lines still poorly explored. In fact, industry has never had these materials available in clean forms, susceptible to the further treatments which they are capable of receiving with profit.
To the myriad forms of paper already in use, was added a new one, potentially capable of absorbing unimaginable quantities of pulp. Paper, impregnated with synthetic resin, laminated and pressed under heat, becomes a hard, tough, strong material new to industry but already filling many jobs. By research, the strength of the product has been greatly increased; by controlling the manner of laminating, strength properties can be built into the finished board according to- need,. a property which distinguishes "papreg" from most artificial boards. The new material is used to form the wearing faces on light cores, thus giving a hard finish and requisite stiffness to lightweight "sandwiches" that seem to have quite broad applicability. It can bonded to metals, or combined with lacquer finishes. In brief here is a new material with strength, durability, and adaptability that can be easily molded to shape and worked in many forms. Paper has become a structural material.
Increasing application of paper to structural fields may be reflected in increased need for high-strength pulps. Strong sulphite and Kraft pulps will probably meet that need, but the newer processes may be expected to develop employable strong pulps.
Complete recovery of by-products of pulping is certain to be widespread eventually as increasing price competition compels the recovery of all possible profits. The sulphite industry in Europe already recovers the sugar from its waste liquors as alcohol or feeding yeast. Some lignin recovery is also accomplished both in Europe and America, but it is unthinkable that the inherent values in lignin, 25 percent of the weight of the wood pulped, should continue to pollute streams and harbors. Shifting to magnesia base cooking liquor, replacing lime bases, and thus making possible complete chemical recovery, will be an important trend. This procedure will do several things: 1) eliminate pollution, 2) recover the fuel value of lignin, 3) simplify recovery of by-product sugar.
The sulphite industry is characterized by full recovery of the chemicals used, and of the fuel value of the lignin. However, the American industry recovers only a fraction of the by-product resins, fats, and volatile oils that are recovered by the North European industry. No sugar recovery is possible in this industry but, as values are developed from lignin, it may be anticipated that sulphate lignin will be isolated and other fuels substituted for it in plant operation.
In addition to laminated, resin impregnated paper for structural purposes, recent excellent progress has been made in the utilization of lignin from the alkaline pulping processes as an impregnating material. Lignin from the soda or sulphate process is recovered, impregnated into either the pulp or paper, and the paper laminated and hot pressed to give a very hard and strong board which has considerably higher impact values than the corresponding "papreg." Considerable progress has been made also in conversion of sulphite lignin to valuable materials.
As competition increases in the pulp industry, it may be expected that all possible sources of additional profits from by-products will be explored.
The numerous variations in form and character exhibited by various types of "fiber boards" and insulating materials produced from wood in some form or other attest again the versatility of the basic material.
Fig. 5. Paper mill at Covington, Virginia
Wood hydrolosis. - Pulping processes are primarily hydrolytic processes: that is, water, under the influence of acid or alkalies, splits wood into its chemical components. One hundred and twenty-five years ago it was found that if the hydrolytic processes were carried sufficiently far, the cellulose and hemicellulose fractions were broken down into sugars. As the composition of the cellulose and hemicellulose became clarified, the nature of the sugars obtained from them also became clear. Generally speaking, these sugars are mixtures of hexoses, exemplified by glucose, and pentoses, exemplified by xylose. The proportion in which these sugars occur as decomposition products of wood varies considerably between hardwoods and softwoods, the former containing a larger proportion of the pentose or five-carbon sugars that are not ordinarily fermentable to alcohol by yeast.
Although the discovery of the formation of sugars from wood was made so early, it is only comparatively recently that any great commercial success has attended this discovery. In general, two lines of industrial development have been followed: very strong acids have been used to decompose the cellulose material, followed by dilution and fermentation, or dilute mineral acids have been used. Each form of process has had its advocates and industrial trial. The aim in all eases is to produce a crude sugar solution of usable concentration and of a character fermentable to industrial chemicals. The rapid development of industrial fermentology within recent years has had considerable importance in the possible production of a very cheap sugar solution from wood because. instead of the recovery of edible sugars, the objective is the conversion of the crude material to further derivatives.
Three general lines of fermentation development are currently under way and may be expected to continue. The first and most interesting during the war was the production of industrial alcohol from the hexose sugars by fermentation with ordinary yeast. After separation of the alcohol, the remaining pentose sugars may be subjected to any one of a number of fermentations that give rise to a series of industrial chemicals, or used as a medium for the growing of feeding yeast, a potentially valuable high-protein component of animal foods. A second important line of development follows the procedure of converting all the sugar yield to feeding yeast or other organisms that convert sugar to protein. A third line makes use of various double fermentations for the production of other materials than alcohol. There is no visible limit to the variety of chemicals possible by these procedures.
The most successful process thus far appears to have been that developed by Scholler in Germany prior to the war, greatly modified and improved by U. S. chemists during the war. Under present U. S. techniques it appears that German plant installation costs will have been radically reduced and efficiency of operation greatly increased without sacrificing yield, which remains in the neighborhood of 1,100 pounds (approximately 500 kg.) of total sugar per ton of dry softwood waste. The process yields from 500 to 600 pounds (approximately 225 to 275 kg.) of dry lignin as a by-product, which for the present will serve as fuel in the industry. However, research in progress gives every promise of developing lignin into a source of industrial chemicals of importance. It is of considerable significance that among the chemicals that have been produced from lignin, are found the very phenols that form such important ingredients of improved wood and paper products. Especially if cheap electric power is available, it is anticipated that the transformation of lignin into chemicals will become an integral part of forest products industry and that products derivable from lignin will be in a large degree incorporated into subsequent manufacture of wood materials.
The profitable conversion of lignin to chemical or other goods may be said to constitute the key to the entire problem of utilization of wood waste. In simple arithmetic terms, for example, 10 pounds (approximately 4.5 kg.) of lignin would be produced for each U. S. gallon (3.7853 liters) of alcohol; thus a return of U. S. $0.01 per pound (0.4536 kg.) on lignin would permit $0.10 a gallon to be taken off the price of alcohol. Demand for cheap alcohol should develop far beyond present supply possibilities; other cheap products of fermentation offer similar possibilities.
The possible utilization of the sugar produced for a diversified line of fermentation products, of methyl alcohol for formaldehyde, of lignin for phenols, and the use of these in the fabrication of wood and paper products, conjures up a picture of diversified chemical utilization of wood that offers tremendous industrial possibilities. This sort of waste utilization, geared to diversified use of wood as wood, constitutes diversified forest utilization, and a basis for a new concept of industrialization on wood.
The possibility of production of abundant and cheap sugar from the forest offers encouraging possibilities for achieving an integration of forestry and agriculture in a good deal of rugged territory with limited agricultural land that has not been possible in the past For example, although summer grazing land may be sufficient for a reasonable livestock economy, the agricultural base for the production of winter feed may be insufficient to produce the feed necessary to carry livestock through a winter; therefore, the livestock base is often definitely limited. The production of protein feed from wood sugar seems to offer an opportunity to increase the protein feed supply in such territories and bring better balance between food supply and population. Likewise, increase in the protein component of tropical diets is a possibility.
There is another way of using these new products of the forest for the improvement of agriculture in the potential use of lignin, by-product of wood hydrolysis, as a humus former and soil builder. It is known that prior to the war Germany was using its lignin from the Scholler process as a soil improver. Work in progress in the United States of America looks toward the employment of lignin as a medium for the application of nitrogen and phosphorus in slowly available form. thus avoiding the usual heavy losses by leaching and employing lignin, a humus forming residue, as a carrier. These possibilities, if they can be successfully applied, may be of large significance to a areas deal of rather poor agricultural territory in which forest acreage is predominant. Fortunately, in the production of yeast, the yield is equally high from hardwoods and from softwoods. This may prove to be of great significance to the tropics, critically short of protein food, abounding in hardwood forests.
Fuel. - The largest use for wood has been as fuel. Generally, however, its use for this purpose has been a crude one, and the true value of the material has rarely been obtained. In countries with thin population and abundant wood, this has not caused any violent distress; but in many regions with heavy populations, limited forests, and no other fuel, the result has been destruction of the forest itself. In industrialized countries, the cost of wood fuel in manpower required for preparation and transportation renders necessary improvements and economies in its use. As it becomes a more important chemical raw material, the worth of wood itself will make imperative refinement of its preparation and use as fuel.
Compared with coal, wood is a bulky fuel. Weight for weight. it has about half the. thermal value of a good coal. Yet, its cheapness, abundance, and cleanness have kept it in a leading position as ordinary fuel. As industrial efficiency has increased, improvements in the mechanisms employed for burning wood have followed. They have taken the same general form as those applied to coal; namely, the recovery of the heat from the total combustion of the volatile gases distilled during combustion. Numerous new forms of heating apparatus for wood, using continuous feed and gas combustion principles, have been developed and are in production.
Further improvements have been made in reduction of the bulk of wood waste from sawmills and manufacturing establishments, thus reducing storage space requirements and lowering transportation costs. These improvements have usually taken the form of compressing the waste into briquettes, blocks, or billets, and have provided very satisfactory fuels, although the cost has usually been too high for universal use.
Considerable thought has been given to the problem of reducing the labor required to prepare wood for use as fuel, at the same time preparing it in a form more adaptable to continuous feeding devices and adapting it to the more modern stoves and furnaces. Mechanization of the traditional sawing and splitting operations is the objective simple, cheap, and effective means of reducing the log to material that can be mechanically handled in bulk.
Combined with these objectives, already rather well along toward realization, is the accomplishment of the use of wood as a source of power for the internal combustion engine. Those countries poor in petroleum are already using a great many motors powered with producer gas made from wood or charcoal. The expansion of this use may be expected because the low cost of the fuel itself will be the determining factor.
Producer gas from wood appears especially attractive as a source of power for relatively small power units on farms or in forest operations themselves. Their adaptability to stationary engines is clear and their use for self-propelling units has already made great strides. Bulkiness of the fuel seems to limit its use in the latter field to trucks and tractors as long as petroleum remains abundant, but, as the cost of gasoline rises, use of wood for motor fuel may be expected to increase, especially in those regions where wood is abundant and well distributed.
In general, producer gas from wood has merely been used in the existing types of internal combustion motors. Adequate study given to matters of compression ratios, rates of feed, and the like should lead to the development of motors especially adapted to wood fuel with greatly improved efficiency.
Either as wood, charcoal, or hydrocarbon fuel, wood can play an important role in the further expansion of the use of the internal combustion engine. Hydrocarbon fuel itself is a promising product of the chemical transformation of lignin and could be a valuable and important by-product of wood hydrolysis.
Thus, for domestic and industrial use, for stationary or mobile power units, the fuel value of wood offers a tremendous, renewable reserve when the temporary supplies of easily available petroleum shall have vanished forever.
It must be apparent that research in forest products utilization, a small segment of the total research effort, must continue at an accelerated pace in order that the forests may contribute their share to advancing civilization and providing comforts to mankind. This research should attack especially the enormous wastes of forests and lumber manufacture. Tremendous research effort toward better ways of doing things and better ways of living is perhaps the outstanding characteristic of twentieth century civilization. As long as civilization is progressing, research will be continued, or conversely, when research ends the development of civilization will also end. Research itself engenders more research. It is especially true that findings in even remote scientific fields make possible new developments in forest products utilization and make necessary further research efforts and industrial developments in that field.
For example, the invention and development of the internal combustion engine has brought about revolutionary changes in transportation. These changes have made imperative the development of new, light, strong forms of construction. These forms must be fashioned from materials that are, available and cheap. It is not yet apparent whether they will be made mostly from light metal alloys or from wood. It is probable that the field will be divided between these materials according to suitable properties. In any case, the development of plywood, molded plywood products, and light laminated products has been a direct result of this demand for new types of structural goods.
It was not possible to make laminated wood products for outside use until chemical industry developed waterproof resin glues. With the development of such glues, their application to the age-old task of joining wood began, with the result that a great number of new applications of wood became apparent.
Thus, new requirements for new products in other fields bring about new industry and new developments in forest products uses, a process that will continue as long as civilization grows.
These new uses for wood make possible real industrialization on a wood base and thus widespread industrialization in territories formerly capable only of producing a crude raw lumber for distant industrial centers, usually founded on a mineral economy. If it is sociologically correct that a dispersion of the large industrial centers to smaller communities is desirable, industrialization based on wood offers a most promising possibility, principally because such industrialization need never terminate because of the exhaustion of the raw material base. No other industrial raw material offers at once the possibility of permanence and universal application that is offered by wood.
In too much of the world the limitation of production to crude goods tends to hold large populations in economic subjection to distant industrial centers. Without important exception, countries producing only crude goods have not developed high standards of living. Neither have high standards developed upon a strictly agricultural base. Industrialization based upon products of the soil can lead to the development of that widespread industrial civilization that seems to offer the greatest possibilities in human welfare. It appears that wood may offer a highly satisfactory base for such development.
The universality in application of wood may be the strongest argument for a wood base. In some form or other it can feed, shelter, clothe, and warm man.
Economic industrialization based on wood must take cognizance of two principles: 1) the raw material is the product of forest growth which is determined in large measure by the character of the harvest. Therefore, industrial use must be adjusted to the rate and character of forest growth in any particular place. Otherwise there will follow unbalanced growth and unsatisfactory raw material supply for industry. 2) A second plan that must be followed is that of diversification of industry so as to use all the growth of the forest in the production of goods; distribution of costs over the entire field makes possible long-range stable industrial development. :Forest industries in the past have been very largely single product industries. They have, in general, mined the forest with little regard for the future except in those old and stable countries where long experience has taught the necessity for good integration of forest use and growth. It is clear that the raw material offers broad opportunity for diversification and that permanence is best ensured by this means.
It is perhaps a truism to state that general human welfare, high levels of health and happiness, are correlated closely with economic prosperity and political stability. The latter two factors are generally inseparable. Fundamentally, the factor with which industrialization on a wood base has most to do is economic prosperity, which must be defined as a full satisfaction of human physical needs at the first level, and satisfaction of human "wants" at an increasingly higher level. There is no foreseeable limit to the height of the latter; it can only be limited by the amount of goods in toto capable of being produced by the application of human intelligence to the materials and sources of energy available to man.
The concept of an expanding economy involves both a broadening and deepening of production of goods; broadening the availability to include all peoples; and deepening the degree to which materials and energy are converted to human use. Wood is a raw material well nigh universal in its distribution, and, where not abundant, it can be grown in abundance on lands not fitted for other uses. It can become in truth the universal raw material upon which to base a major part of international activities that look toward not only the alleviation of the poverty that lies at the root of the world's ills, but the raising of the general level of availability of goods.
FAO would appear to offer an excellent medium for accomplishing certain necessary tasks preliminary to the wide industrial development based on wood that is contemplated. Undoubtedly, most such development must take place by the enlistment of private capital, which must be encouraged by accurate engineering and economic data as well as demonstration of the possibility of adequate markets. The importance of the material involved renders it international in character.
A central organization designed to collect, correlate, and review data on technical and industrial developments is of first importance. Research in forest products technology has been under way in many countries for many years, but dissemination of the information obtained has been left too much to chance, too much to scientific publications. The objective is the application of newly won scientific knowledge to actual industrial operation. Publication of scientific data is insufficient; it must be applied in an industrial way.
This can be accomplished through two principal processes: 1) the systematic dissemination of the information collected and analytically reviewed; and 2) the arranging of pilot and demonstration plants according to the special needs and possibilities of nations, regions, or territories. It has been apparent that there is a long time lag between production of research results in forest products utilization and their translation into industry. The lag arises partly from the inertia of industry and private capital and partly from the fact that most research in forest products utilization has been executed by governments. There has been inadequate opportunity for the transferring of scientific knowledge thus obtained into actual operating industries with full protection of public interest and opportunity for private gain. FAO should be in an excellent situation to bridge this gap, to adduce all available information on the subject and put it to work in the major task of drawing goods from the world's renewable forest wealth.
Photographs accompanying this article are reprinted by courtesy of the following: Figs. 1 and 6 - Dominion Forest Service, Canada; Figs. 2, 3, 4, and 5 - U. S. Forest Service.
