6 
solved tar. For the acetic-acid and dissolved-tar determinations 
100 c. c. of pyroligneous acid were distilled at a maximum tempera- 
ture of 140° C. until practically no further distillate appeared, when 
50 c. c. of water were added and distilled off as before. The residue 
in the flask was weighed and computed as dissolved tar, while for the 
acetic-acid determination an aliquot part of the distillate was ti- 
trated with normal sodium hydroxide solution, with phenolphtalein 
as indicator. 
The wood alcohol was determined by distilling 60 per cent from a 
1-liter sample of the pyroligneous acid and adding an excess of sodium 
hydroxide to the distillate, again distilling 60 per cent, and after 
again adding sodium hydroxide, making a third distillation of 60 per 
cent. The final distillate was accurately weighed, and the specific 
gravity determined by means of a Westphal balance at room tempera- 
ture and corrected to 15° C. by using the tables of Dittmar and' 
Fawsitt. 1 In correcting the specific gravity for temperature it is 
necessary to consider both the concentration of alcohol and the range 
of temperature. 
TAR. 
The amount of acetic acid in the settled tar was determined, after 
Klar, by distilling 100 grams of the tar at 130° to 140° until the 
watery distillate ceased, then passing steam through the residue until 
no more acid was found in the distillate, the latter being then titrated, 
as in the pyroligneous-acid analysis, and added to that found in the 
pyroligneous acid. 
COMPUTATION OF RESULTS. 
All the yields of products were first computed to a percentage of 
the dry weight of the material distilled, since only on this basis are 
the results directly comparable, the effect of varying percentages of 
moisture in air-dry wood and of differences due to weight per unit 
volume being eliminated. But because the unit of measurement for 
wood is the cord, and the capacity of a plant is naturally expressed in 
this unit, a comparison between the various species is made also on 
the cord basis. A cord was assumed to contain 90 cubic feet of actual 
wood, and its weight was derived from the average weight per cubic 
foot of air-dry wood of different species as given by Snow. 2 
The actual volume of a cord differs, of course, for different forms 
of material, due to variation in diameter and shape among the indi- 
vidual pieces. Also, differences in density exist between wood from 
different parts of the tree and between wood and bark; hence between 
forms of material containing different proportions of wood and bark. 
For these reasons it was impossible to estimate closely the weight 
per cord of the several forms as compared with each other, and the 
1 Trans. Roy. Soc. Edin., vol. 33. Quoted in Smithsonian Physical Tables. 
2 The Principal Species of Wood, by C. H. Snow. 
