2 BULLETIN 508, U. S. DEPARTMENT OF AGRICULTURE. 



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 gray 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 mpthods of analysis are given in Klar's Teclinologie der Ilolzverlcolilung, p. 337, 

 except that in the alcohol analysis a final distillation is made after adding a few cubic 

 centimeters of concentrated HsSOi to eliminate the wood-oil constituents. 



2 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. 



