THE WOODS OF THE UNITED STATES. 



251 



It will be noticed that all species in which the wood is heavier than water belong to the semi-tropical region 

 of Florida or to the arid Mexican and interior Pacific regions. There seeing to be a certain, but by no means constant 

 relation, as shown in this table, between aridity of climate and the weight of the wood produced by closely allieu 

 species or by individuals of the same species. The wood of the form of Qucrcits r libra peculiar to western Texas is 

 nearly 30 per cent, heavier than the average of all the specimens of the typical speci es grown in the northern 

 states. Among the white oaks the wood of species belonging to regions of little rainfall, Qucrcus grisea, ollongifolia, 

 Durandii, and Douglaxii, is heavier than that of allied species peculiar to regions more favorable for the growth of 

 trees. The average of two specimens of Quercus prinoides grown in western Texas is 19 per cent, heavier than 

 the average of all the other specimens of this species grown ia other parts of the country. In Fraxinus, the wood 

 of F. Grcggii of the Eio Grande valley is heavier than that of any other species ; it only just surpasses in weight, 

 however, the wood of the western Texas form of F. Americana, which is 20 per cent, heavier than the average of 

 all specimens of the typical species grown north of Texas. On the other hand, th e wood of Texas forms of Fraxlnwt 

 mrid'ut is constantly lighter than that of northern specimens, and the wood of Celtis grown in Arizona is lighter 

 than that of the average of all the other specimens of this species. In Juglans, the heaviest wood is that of J. rupestris, 

 a species belonging to a region of little rainfall, and a specimen of J. nigra from western Texas is 33 per cent, 

 heavier than the average of all specimens grown in the Mississippi basin. In the case of Platanus, the heaviest 

 wood is that of the Atlantic species, but wood of the species peculiar to the comparatively moist climate of 

 southwestern Arizona is, however, considerably lighter than that of the drier climate of southern California. 



, FUEL VALUE. 



The relative fuel values are obtained by deducting the percentage of ash from the specific gravity, and are 

 based on the hypothesis that the real value of the combustible material in all woods is the same. 



A number of analyses was also made of the wood of several of the principal trees of the United States (Table 

 II) and their absolute fuel value calculated. Mr. Sharpies describes the methods adopted by him to obtain these 

 results, as follows : 



The carbon and hydrogen determinations were made by the ordinary processes of organic analysis, by burning the wood in a current 

 of oxygon. The moisture was determined by drying the wood at 100 centigrade until its weight became sensibly constant. The 

 calculations were then made on the dry wood. The results contain a slight constant error, arising from the fact that the nitrogen in the 

 wood was ot determined. This error is, however, very slight, the nitrogen, which is included in the percentage of oxygen, rarely 

 amounting, in any wood, to one per cent. The column headed " Hydrogen combined with.oxygen ", is found by dividing the amount in 

 the column headed "Oxygen" by eight, and represents the hydrogen that may be considered as already combined with oxygen in the form 

 of water, and is therefore useless for fuel. The fuel value per kilogram is found by multiplying the percentage of carbon by 8,080, and 

 that of excess of hydrogen by34,4b'2 (these being the values obtained by Favre and Sil1>erman), adding these together and deducting from 

 the sum the product of the total hydrogen multiplied by 4,833, which represents the heat required to evaporate the water produced by 

 burning the hydrogen. The constants used above represent the number of kilograms of water raised one degree centigrade, by burning 

 one kilogram of carbon or hydrogen. The fuel value per cubic decimeter is found by multiplying the value per kilogram by the specific 

 gravity. It need hardly bo said that this fuel value is rarely attained in practice, and that it is never utilized. There are too many 

 sources of loss ; the calculation supposes that the combustion is perfect, that no smoke is given otf, and that the heat of the products of 

 combustion, with the exception of that neeessary to convert the water into vapor, is all utilized. 



It appears from Mr. Sharpies' experiments that resinous woods give upward of 12 per cent, more heat from 

 equal weights burned than non-resinous woods; the heat produced by burning a kilogram of dry non-resinous 

 wood being about 4,000 units, while the heat produced by burning a kilogram of dry resinous wood is about 4,500 

 units, a unit being the quantity of heat required to raise 1 kilogram of water 1 degree centigrade. 



Count Eumford first propounded the theory that the value of equal weights of wood for fuel was the same 

 without reference to specific distinctions; that is, that a pound of wood, whatever the variety, would always 

 produce the same amount of heat (Count Bumford's Works, Boston, 1873, vol. ii). Marcus Bull, experimenting 

 in 182C upon the fuel value of different woods (Trans. Am. Phil. Soc., new ser., iii, 1), found a variation of only 11 

 per cent, between the different species tested. Eumford's theory must be regarded as nearly correct, if woods are 



