THE PHYSICAL PIIOPERTIES OF WOODS. 23 



116. Percentage of Ash. Two determinations of ash were made 

 from each specimen studied by burning small, dried blocks in a muffle 

 furnace at a low temperature. Of the four hundred and two species 

 studied, the range of variation was found to be from 0.08 (in Libocedrus 

 decurrensj the Incense Cedar, and Pseudotsuya Douylasii, the Red Fir,) 

 to 9.28 (in the Yucca elata, a kind of Spanish Bayonet). 



117. Relative Approximate Fuel Value. The relative fuel 

 values were obtained by deducting the percentage of ash from the specific 

 gravity and are based on the hypothesis that the real value of the com- 

 bustible material in all woods is the same. It appears from Mr. Sharpies' 

 experiments that resinous woods give upwards of 12 per cent more heat 

 from equal weights burned than non-resinous woods. In ordinary prac- 

 tice, however, less heat is derived, because so much more carbon escapes 

 unconsumed in the form of smoke than with the non-resinous woods. But, 

 making the distinction of resinous and non-resinous woods, the amount of 

 heat derived is very nearly in direct proportion to the specific gravity, i. e., 

 the heavier the wood the greater the amount of heat obtained, supposing, 

 of course, the woods to be equally seasoned. There is always more or 

 less heat lost in combustion, besides that resulting from the escape of 

 the carbon and hydrogen of the smoke. A certain amount is required 

 to evaporate the water which is always present ordinarily in the pro- 

 portion of 25 per cent or more in air-dried wood. These items of loss 

 were eliminated in Mr. S/s experiments so that his results show only 

 approximately the amount of heat derived in ordinary practice. The 

 amount of ash present in a wood lessens proportionally the amount of 

 derived heat, but this item is usually very slight. 



The unit of fuel value would be represented by a wood free from ash 

 (which is not found in reality) and a specific gravity of 1. Of the four 

 hundred and thirty species experimented upon, there was found a varia- 

 tion from 0.2480 (in Yucca baccata, the Spanish Bayonet) to 1.1938 (in 

 Condalia ferrea, the Black Iron-wood). The relative fuel value of any 

 particular wood multiplied by 4000 would give very nearly the amount 

 of heat obtained by burning a cubic decimeter of that wood a unit of 

 heat being the amount required to raise a kilogram of water one degree 

 centigrade ; and 4000 units being the amount of heat produced by burn- 

 ing a kilogram of dry non-resinous wood. With resinous woods the 

 amount lost in the smoke 12 per cent or more must be considered. 



118. The Elasticity of Woods was experimented upon by Mr. 

 Sharpies, and this he represents by designating the Coefficient of Elas- 

 ticity, which is the ratio of the force required in distorting the wood to 

 the amount of that distortion, which must not be beyond the elastic 

 limit. By distortion is meant either extension or compression, which are 

 both brought into play in the process of bending. The coefficient of 

 elasticity, as determined by Mr. S., represents the weight in kilograms 

 which would be sufficient to elongate a stick one centimeter square to 

 double its original length, were that possible, which, of course, is not. 

 the case, as the fiber would part long before that limit is reached, but it 

 is a convenient method of comparison. The experiments on three hun- 

 dred and ten species of our native timbers shows a range in coefficient 



