Mai-cb 10. 1917 



PIP 



Value of Weight in Wood 



B.v Maxwell 



Editor's Note 



Few articles in general use are more subject to changes in weight than wood. A plank 

 when dry may not be half so heavy as when green ; and, after it has become light by seasoning, 

 it may recover its former weight by absorbing moisture. There is. however, a point bejow which any 

 wood's weight cannot be reduced, and there is also, a pretty definite limit beyond which it cannot be 

 increased. The spread between the lightest and the heaviest woods is equal to si-K or eight times the 

 weight of the lightest. No other property or quality of wood is so intimately associated with cost as is 

 weight. It in some way touches the matter of money at almost every turn. It is taken in considera- 

 tion more frequently than any other one property or quality pertaining to wood. 



HEAVY WOOD EMPL 



ARTICLE FIVE 



The man who pays a freight bUl on a shipment of lumber has the 

 fact forcibly impressed upon his mind that wood has weight. The 

 xinnual freight bill on forest products in the United States cannot be 

 much imder $80,000,000, though nobody knows the exact amount. 

 Freight may be paid several times on the same material, first as logs, 

 then as rough lumber, and one or more times afterwards in the final 

 distribution of the finished products. 



Many attempts have been made to compile tables showing the ship- 

 ping weights of lumber and logs, but no such tables have ever been 

 generally accepted, and none ever wiU be. Such a table fol- lumber of 

 particular species in one region, or for lumber of a certain state of 

 dryness, will not do for the same or related species of another region, 

 nor for lumber of a different degree of dryness. But the chief reason 

 that a shipping-weight table cannot be depended upon for lumber is 

 that the condition of seasoning must often be more or less uncertain. 

 The amount of water remaining in the wood 

 •cannot always be known, even approximately. 

 Moisture may constitute half the weight of 

 green lumber and not ten per cent of the sea- 

 soned article. That is a wide range to guess at. 

 If a wood weighs three thousand pounds when 

 five hundred pounds of the weight is water, it 

 wUl weigh more or less as the quantity of water 

 increases or diminishes, and this disturbing 

 and uncertain factor must always threaten to 

 affect tables of lumber shipping weights. 

 Nearly any kind of lumber is capable of hold- 

 ing a pint of water to the board foot of wood, 



and some will hide away twice that much without any of it being 

 visible. The best that can be claimed for any shipping-weight table 

 . for lumber is a range of averages, and an avergae is an unreliable 

 thing. 



Wood's Absolute Weight 



American woods when reduced to oven-dryness, range in weight 

 per cubic foot from less than ten to over eighty potinds. Yet the real 

 weight of wood substance, with everything else excluded, is as fixed 

 and definite as is the weight of gold or any other metal. Pure wood 

 weighs almost exactly 100 pounds per cubic foot, and it weighs the 

 •same whether it is white pine, live oak, or any other species. To 

 :show such weight it must, however, be reduced to an absolutely solid 

 mass, with air spaces and impurities removed, and nothing present 

 but real wood substance. It is next to impossible to do this in 

 practice, and pure wood is more or less theoretical outside the chem- 

 ical laboratory. The condition may be approached, however, by heat- 

 ing wood in the presence of water under great pressure. It is, by that 

 process, transformed into a substance resembling horn in appearance, 

 and of greatly increased weight in proportion to volume. A thousand 

 board feet of pure wood would weight 8,300 pounds. 



Wood in its natural state is extremely porous. Some of the larger 

 pores, as in oak, ash, chestnut and hickory, may be seen with the naked 

 eye, but the smaller cavities are invisible except under a microscope. 

 When thus examined, wood is discovered to be of a structure as open 

 as honeycomb. 



The lighter the wood, the more open and porous the structure. A 

 block of white pine, for instance, is three-fourth cavities and one- 

 fourth real wood substance. The cells and other openings are filled 

 -with air and water. In thoroughly soaked wood they are largely filled 



with water, but as the Wyood seasons, the water passes away and its plac« 

 is taken by air. It is not possible in practice to take aU the water 

 out of wood, though nearly all may be expelled by applying heat. 

 That which occupies the large open cavities comes away most readily; 

 from the minute openings the expulsion is slow. Some water, it is be- 

 lieved, is held in the almost infinitely small interstices between the 

 ultimate crystals which, as is supposed, constitute the walls of wood 

 cells, but which interstices are too small to be seen by the most 

 powerful microscope. Such water, amounting possibly to one or two 

 per cent of the weight of the wood, cannot be expelled without burn- 

 ing the wood. The cedar of an Egyptian mummy case which has 

 seasoned since the days of Amenhotep, stiU contains a quart or two 

 of water, held there since the tree grew on Lebanon. 

 Deducing The Weight 

 The various processes of seasoning wood are applied for the purpose 

 of removing the water, whereby the wood is put in condition for use. 

 The saving of freight is not always of para- 

 mount importance, but it often is. 



A thousand feet of green lumber of almost 

 any wood may have its weight reduced a 

 thousand pounds by expelling some of the 

 water. When a portion, but an indefinite 

 portion, of the water has been removed, the 

 lumber has reached what is called ' ' shipping 

 weight." That is no fixed weight. It does 

 not mean that the lumber still contains only 

 a stipulated per cent of water. 

 OrED IX C.\RVING. The oven-dry weights of aU the ordinary 



woods of this country are known. When 

 "oven-diy" is thus used, it means that the wood is so nearly dry 

 that it ceases to lose weight under heat no. more than suflSeient to boil 

 water. If the oven-dry weight and the shipping weight of a wood are 

 known, the amount of water still in the wood may be ascertained by 

 subtracting the oven-dry from the shipping weight. 



Suppose, for the sake of illustration, that when lumber is spoken of 

 as shipping dry, it still has twelve per cent of moisture in it. That 

 is, the water in it is twelve per cent as heavy as the same wood when 

 oven-dry. Under such circumstances, the shipping weights of certain 

 woods are shown in the following table: 



Pounds Pounds 



per M feet per M feet 



with 12% with 12% 



HARDWOons. moisture haudwoods. moisture 



Balm of gilead 2,100 Sugar maple 4,000 



Cottonwood 2,100 Mahogany 4.200 



Yellow poplar 2.450 White oak 4.300 



Black willow 2,600 Persimmon • 4,600 



Chestnut 2,600 Forked leaf white oak 4,800 



Basswood 2,650 Shellbark hickory 4,850 



Buckeye 2,650 Southern red oak 5,250 



Tupelo 3,000 softwoods. 



Soft maple 3,100 .\rborvitae 1,850 



Sycamore . . . : 3,300 White pine 2,250 



Red gum 3,400 Redwood 2,450 



Wild cherry 3.400 Hemlock 2,450 



Black walnut 3,750 Cypress 2,550 



Nortbern red oak 3,800 Black spruces 2,700 



Yellow birch 3,800 Western yellow pine 2,750 



White ash 3,800 Southern red cedar 2,850 



Beech 3,950 Douglas fir 2,950 



Rock Elm 4,000 Western larch 3,650 



Soft elm 4,000 Longleaf pine 3,950 



Utilization Influenced by Weight 

 Wood is employed for many purposes where weight is not directly 

 considered. That is generally true of lumber and timber for structural 

 uses. It is not customary to select a wood for fences, walls, or roofs 



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