6 BULLETIN 129, U. S. DEPARTMENT OF AGRICULTURE. 



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. 



