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 on 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 300° F. 
Available heat units 
per cord of 90 solid |Per cent ofshort- 
cubic feet (in mil- | ton coal value. 
Species. lions B. t. u.). 
Air-dry. | Green. | Air-dry.| Green. 
Aer Ted: CA AOTCRONA) cece se wicca a alse he Sleldec cine nemetaemeee 14.8 13.0 57 50 
Ashe biltmore/ GE: bilftmoreana) 222 222 2. ode cec es eens ee. 20.7 20.0 80 77 
IBIACk: CHummicra) caterer ne Wet ne ou SNnehiel Ay Gore 18.5 16.5 71 64 
Blue (Hh aquadranculata) cesses elas se eaoe ee ein 21.3 20.7 82 80 
Green’ GH slancCeolatay yaks cece oes ete eae ea tay eI Reel 20.6 19.6 79 75 
Oregon CES Onezoma) ey Sea eM al i Se Ulla ete 19.7 19.0 76 73 
Pumpkin (hy prolinda) teas eae ce see eee eee 19.4 18.2 75 70 
White. Ghvameri Gama) sees oG2 eee le ee Oa eS elaae 20.5 19.9 79 77 
RVVNIEE (SECON AIST O Mita) hate nei e snares Lie oe I A es aces a 23.0 22.4 88 86 
IA’ Spen! GhetremullOides) ease vaya meme terre ee epee RL ate 14.1 12.1 54 47 
Wargetooth (EP. erandidentata)ssa-cs. een eae ee 14.2 12.4 55 48 
Basswood) Che ame;niCan a) sree see eis eee ie ere ern eae 12.6 11.0 48 42 
IB CECH GEN ATROPUTICEA) hice eee years ree epee ees omy tenta yey Airs many aes 20.9 19.7 80 76 
iBirchYipaper(s. papyritera) aoe se aes ee eee ee eee eee 18.2 16.7 70 64 
FSi e1e] Bat Gl Bag Cove rz) ley Mean eh nia nace ail be Ub Na RN BS INL 23.3 21.9 90 84 
Viellow.GB. Tata) sve Wied We Os RN eit PNT 20.9 19.4 80 75 
Gray CB pOpuUlitOligny reper aE Lee pero 17.5 16.1 68 62 
Red GBemigna les othe aye aa. SO eRe see ee aa 17.5 1537 68 60 
1 Gray and red birch estimated. 
