2 BULLETIN 508, U. s. DEPARTMENT OF AGRICULTTJRE. 
tice are well known. Laboratory methods of distilling are not com- 
parable directly with commercial conditions, and the calculated 
yields per cord from laboratory distillations on 100 or 200 pounds of 
material are frequently much higher than the yields from distilling 
several thousand pounds in the commercial plant. 
PLAN OF INVESTIGATION. 
The apparatus used and the manner of making the tests are de- 
scribed in Bulletin 129. Both body and slab wood were distilled in 
most cases and in a few species limb wood was included in the study. 
The yields of wood alcohol and acetic acid were determined by 
analysis of the pyroligneous-acid liquor/ and the amount of tar and 
charcoal was determined by measurement. The average was taken 
of three or four tests on each form of material. 
METHOD OF RECORDING DATA. 
The yields are expressed in three ways: (1) As a proportion of the 
oven-dry weight of the wood distilled (it is only on this basis that 
the results are independent of varying percentages of moisture in 
the material and of differences in the weight of unit volumes) ; (2) 
in the commercial units, gallons of 82 per cent crude wood alcohol 
and pounds of 80 per cent gi^ay acetate of lime per cord of air-dry 
wood; 2 and (3) as a proportion of the yield of a cord of equal parts 
of beech, birch, and maple. 
YIELDS ON PERCENTAGE WEIGHT BASIS, ALCOHOL AND ACETIC 
ACID. 
VARIATION AMONG SPECIES. 
The average yields of acetic acid and wood alcohol expressed in 
percentages based on the oven-dry weight of the material distilled 
are given in Table 1. The yields from a previous study of the 
standard species, beech, birch, and maple, are given for comparison. 
On this basis several of the species tested compare very favorably 
with the standard species. White elm, slippery elm, silver maple, 
and black ash gave nearly the same yields of alcohol as beech and 
hard maple. The acetic-acid yield of white elm, silver maple (heart- 
wood), tanbark oak, and California black oak (limbs) were very 
nearly the same as that of birch, and considerably larger than the 
yield of beech and maple. 
1 The methods of analysis are given in Klar's Technologie der Holzverkohlung, p. 337, 
except that in the alcohol analysis a final distillation is made after adding a few cubic 
centimeters of concentrated H0SO4 to eliminate the wood-oil constituents. 
~ A cord of air-dry wood is assumed for purposes of comparison to be equal to 90 cubic 
feet of solid wood containing 15 per cent moisture (calculated on the dry weight). The 
weights per cubic foot of wood are those given in " The Principal Species of Wood," by 
C. H. Snow. Recent investigations by the Forest Service show weights per cubic foot 
slightly different from those used in these calculations, but the relative values are not 
changed. 
