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The Weight of Wood 



Lumbermen often discuss the shipping weights of different woods, 

 and surprise is frequently expressed that no official or reliable table 

 of weights exists to guide lumbermen in figuring out how much a 

 thousand feet of lumber of a certain kind will weigh,, or what wOl 

 be the weight of a carload of such lumber, or how many thousand 

 feet will load a ear of a given capacity. It is well known how 

 much a given bulk of coal, coke, iron and many other substances 

 weighs, but there is no definite standard showing what a thousand 

 feet of lumber weighs. 



There never will be such a table. From the nature of the case 

 it is impossible, except within a certain degree of approximation. 

 If one kind of wood only were considered, as white oak or yellow 

 poplar, it would still be impossible to name a weight which would 

 hold true in all cases. Some shipments would be heavier, some 

 lighter, depending chiefly on the dryness of the wood, but also on 

 several other factors. This can best be made clear by showing on 

 what the weight of a certain wood depends, and what is likely to 

 affect it. 



The actual weight of wood — the real wood substance, with all air, 

 ■water and other foreign matter excluded — is as constant as the 

 weight of iron, lead X)r any other metal. If we could get down to 

 actual wood, and deal only with that, there would be no disagree- 

 ments over weights, for so many cubic feet would always weigh so 

 much, n^ver more, never less. But to deal with the matter in that 

 way is impossible in practice. Chemists handle pure wood sub- 

 stance; lumbermen never do, and probably never will. 



Ordinary wood, as everybody knows, is made up of cells, tubes, 

 fibers and the like, most of them too small to be seen except with a 

 microscope. The mass may be compared to a wasps' nest, but it is 

 more complex than a wasps' nest. The cells and tubes form an 

 intricate mass, complicated in the extreme. To the naked eye it 

 looks like a solid body, but it is far otherwise. In some woods, as 

 oak and chestnut, some of the pores are large enough to be seen with- 

 out a glass, but the real cells are very much smaller. 



If a piece of wood could be squeezed until all the water, air, 

 etc., were expelled, it would be practically a piece of solid wood 

 substance. What would that weigh per cubic foot? In round 

 numbers, it would weigh one hundred pounds. A cubic foot of it 

 would weigh just the same whether it were white pine or ironwood. 

 That is, all real wood substances are the same and, bulk for bulk, 

 weigh the same. A thousand board feet of real wood (a thing 

 impossible in practice) weighs about 8,333 pounds. No tree of the 

 known world is that heavy, therefore such a thing as pure wood in 

 practice is impossible, or at least unknown at this time. 



Yet small pieces of practically pure wood are not hard to obtain, 

 with proper apparatus. Wood cells are nearly pure wood substance 

 after air and water are gotten rid of. They sink in water. They 

 are exceedingly small and are generally invisible, except with a 

 microscope. A hundred thousand of them would not make a cubic 

 inch. They are shaped somewhat like matches, and are laid side by 

 side and end to end to form a mass of wood. They are hollow, and 

 the cavities are filled with water, air, starch, sugar, albumen, tannic 

 acid, and other substances, solid and in solution. The spaces between 

 them are filled in the same way. 



Green lumber weighs more than dry because the cavities in the 

 wood contain more water. When seasoning begins, some of the 

 water passes out, and either air takes its place, or the wood shrinks 

 to close the cavities that are emptied of water. The more water 

 gotten rid of, the lighter the lumber. 



The reason that no fixed weight can be named for a thousand feet 

 of any particular wood is that the quantity of water remaining in 

 it is more or less uncertain. Other things affect the weight, but 

 water is the most important in practice. 



A thousand feet of green lumber may contain 2,000 pounds of 

 water. It is impossible to drive out more than nine-tenths of this 

 water by air-seasoning alone, no matter how long it is left in the 

 piles. In practice, the best air-dried lumber has much more than 



—34— 



ten per cent of its original water in it. It is in the cells, in the cell 

 walls, and in the starch and other substance in the various cavities, 

 and wind and sun cannot compel it to let go and get out. Therefore, 

 in calculating the weight of air-dry lumber, the amount of water 

 remaining in it must be considered but cannot be accurately measured. 

 One lot of lumber is not a sure guide for another, because they may 

 not be equally dry. A thousand feet of one may easily contain 

 three or four hundred pounds more water than another, with no 

 easy way of finding out which is most nearly dry. 



No dry-kiln can drive all the water out of wood without heating 

 it sufficiently to destroy the fiber — make charcoal of it. Therefore, 

 there is no such thing in practice as absolutely dry wood. The person 

 who weighs lumber always weighs more or less water with it. Below 

 is a list of several important hardwoods, with figures showing the 

 weights per thousand board feet, if the lumber were absolutely di'y — • 

 that is, as dry as it could be made without heating it sufficiently to 

 burn it. Of course, that condition is never reached in practice, and 

 hardly ever nearer tlian ten per cent. 



.\bsolutelv dry weight 

 Wood — per 1,000 tee't B. M. 



Cottonwood 2,020 pounds 



Yellow poplar 2.197 pounds 



Basswood 2,350 pounds 



Tupelo 2,697 pounds 



Soft maple 2,737 pounds 



Sycamore 2,940 pounds 



Cherry 3.023 pounds 



Red gum 3,070 pounds 



Black walnut 3,176 pounds 



■White or gray elm 3.379 pounds 



Red oak 3,396 pounds 



White ash 3,397 pounds 



Beech 3.574 pounds 



Sugar maple 3,590 pounds 



Cork or rock elm 3,771 pounds 



Locust 3.800 pounds 



White oak 3,862 pounds 



Sweet birch 3,956 pounds 



Persimmon 4,107 pounds 



Shagbark hickory 4,347 pounds 



No shipper need ever expect to handle lumber of the different 

 species with as low ^'eights as those given, because no dry-kiln turns 

 it out in that state of dryness. The weights above given were 

 calculated from laboratory samples heated to 212 degrees and kept 

 at that temperature until they ceased to lose weight. 



The only practical value of the above table is that it enables a 

 shipper of any wood listed to determine approximately how much 

 water he is paying freight on. For example, 20,000 feet of abso- 

 lutely dry Cottonwood weighs 40,400 pounds. If the shipping weight 

 of a car of 20,000 feet is 60,000 pounds, about 20,000 pounds of it 

 is water. A comparison of the shipping weight per thousand feet 

 for any of the woods with the dry weight as shown above, will give 

 approximately the quantity of water still in the lumber. It will 

 often be found ranging from one-fourth to one-third the weight of 

 the lumber. 



It should be borne in mind always that figures showing weights of 

 lumber are only averages and approximations. They are as near as 

 can be attained in practice, and are bound to vary more or less. 



Though the absolute weights of all woods — the real w'ood sub- 

 stance with all water and other substances excluded — are believed to 

 be the same (about 1.6 times as heavy as water), there is remark- 

 able difference in the weights of different woods as they are found 

 in practice. Some are three or four times as heavy as others. The 

 sis lightest woods of the United States are generally understood to 



be the following: 



Pounds 

 per cubic foot 



Giant cactus of Arizona 19.87 



Northern white cedar of Michigan 19.72 



Gumbo limbo of Florida 18.71 



Big tree of California 18.20 



Yucca of California ,. 16.97 



Golden flg of Florida 16.30 



