28 BULLETIN 753, U. S. DEPARTMENT OF AGRICULTURE. 
These 74 pounds are made up of 37 pounds of carbon, 4.4 pounds of 
hydrogen, and 382 pounds of oxygen. The oxygen combines with 
the hydrogen in the proportion of 8 to 1, producing 36 pounds of 
water and leaving four-tenths of a pound of hydrogen to produce 
heat. The total amount of water to be evaporated becomes 25 plus 
36, or 61 pounds; the amount of wood substance left available for 
heat production is 37.4 pounds out of the original 100 pounds. 
It is evident that the greater the proportion of water the less the 
amount of available heat. Only about one-half of the weight of 
wood substances produces heat, while every pound of water com- 
bined in the wood requires 1,108 units of heat to evaporate it, from 
ordinary room temperature (70° F.). Hence under the most favor- 
able circumstances the heating efficiency of a pound of wood con- 
taining 25 per cent moisture will be less than that of dry wood not 
only by the 2,000 units representing the weight of wood replaced 
by water, but also by one-fourth of 1,108 units, or 277 units, so that 
its heating value is but 5,723 units instead of 8,000, or 72 per cent of 
that of a pound of dry wood. On the other hand, if we take the 
pound of wet wood and dry it out absolutely, so that it weighs 
three-fourths of a pound, it will have 6,000 heat units, an increase in 
heating value due to drying of only about 5 per cent. 
COMPARATIVE VALUES OF DIFFERENT WOODS. 
The comparative values of fuel of various species of American 
woods are shown in Table 8. These values are necessarily some- 
what approximate but afford a good basis for comparison of the 
different species. 
Taste 8.—Heat values of cordwood, based qn Forest Products Laboratory 
(Madison, Wis.), weights for oven-dry, air-dry, and green woods and assum- 
ing 7,350 B. t. u. available per pound of dry wood with flue gases at 800° F. 
Available heat units 
per cord of 90 solid |Per cent of short- 
“ cubic feet (in mil- | ton coal value. 
Species. lions B. t. u.). 
Air-dry. Green. Air-dry.| Green. 
Alder red CAcOregong) sec cenericecac cacccco- ue nscaeoneee sate 14.8 13.0 57 50 
Ash* biltmore (F. biltmoreama)..-..2 022.000... 05. cco ccec eee cess 20.7 20.0 80 77 
Blacks (h Mniera) ste ee Se ORS 18.5 16.5 71 64 
Blue imaguadranculata) passe. se see -ccece ocece woe ee eee 21.3 20.7 82 80 
Green! (Halanceolata)=so2. 6 jogen< cic oc oon oe tees eee anstoe 20.6 19.6 79 75 
Oregon GE XOregona) Fase eee eo a ae eee 19.7 19.0 76 73 
ERT kan CH LOLUTI Ca) eevee er ee een en 19.4 18.2 75 70 
RW te GE AMOeriCANS) exec ee sels Se cain cea eee 20.5 19.9 79 77 
sVVhi te; (SecondserOwal)) Bae nee mene tne eee ee ees 23.0 22.4 88 86 
‘Aspens@itremuloides) ee eee AE es Se 14.1 12.1 54 47 
Largetooth (P. grandidentata)..-...............-.---.------ 14.2 12.4 55 48 
Basswood (CE Samericanay ys sie este clea Haass ek te tare 12.6 11.0 48 42 
iBeéch: CE atropuniced) sess cee eS Re a 20.9 19.7 80 76 
Birch paper’ papyLilers) = emer osc e cee eee ee eee eee neee 18.2 16.7 70 64 
DP weet GB ental we sete apie ase aes ee ta ee ED 23.3 21.9 90 84 
Melo wAGB Tite) eee Eee RR ie ee Ue CI elie en 20.9 19.4 80 75 
Gray GB spopulifolia) a ee a ep ea eee. 17.5 16.1 68 62 
Ried /@Bemiera lak sect ccecictemeccee seek: sate ou series 17.5 15.7 68 60 
1 Gray and red birch estimated. 
