Sept. 2,1918 
Acidity of Silage Made from Various Crops 
397 
were then freed from their barium salts by the addition of a theoretical 
amount of sulphuric acid. After filtering off the barium-sulphate precip¬ 
itate, the solution was made up to a definite volume and the volatile 
acid determined quantitatively. The juice which remained after sepa¬ 
rating the volatile acids from the nonvolatile acid under reduced pressure 
was used for the nonvolafile-acid determination. 
methods used in determining the acids of sieage 
Volatile Acids 
The Duclaux method was used in determining the volatile acids. Until 
the recently proposed method of Dyer (5) it was the only method which 
proved applicable in the estimation of small amounts of volatile acids 
when present in a mixture. This method was previously used in studies 
on com silage, and since a complete discussion has been taken up under 
the previous citations, no explanation of the principles involved will be 
given here. It has been used by numerous investigators in determining 
volatile acids in known and unknown mixtures. Criticisms have been 
made of the Duclaux method by Upson, Plum, and Schott (15). Some 
of the criticisms concerning the difficulties involved in carrying the 
analysis by the Duclaux method the writer fully appreciated in previous 
work with mixtures of volatile acids. But experiments in determining 
known mixtures of acids have shown that under the most carefully 
regulated conditions of distillation, accurate results are obtained and the 
writer believes that the method deserves greater confidence than given 
it by the above-mentioned investigators. 
Voitkevich ( 16 ) has obtained results on known mixtures of acetic, 
propionic, and butyric acids which differed not more than 5 per cent 
from each other, and this difference is attributed to the variations in 
the conditions of distillations. He concludes that the method will 
yield accurate and trustworthy results when carried on under carefully 
regulated conditions. 
Dyer has proposed an excellent method which is more simple to ma¬ 
nipulate. The method involves the distillation of the acids in a current 
of stream from a constant volume. The titration figures are plotted 
in the form of curves which are characteristic for each acid. 
More recently Gillespie and Walters (9) published methods for calcu¬ 
lating algebraically and graphically the amount of volatile acids in a 
mixture. The methods of calculation suggested by them are applicable 
to either the Duclaux or Dyer method, as the methods of calculation 
are applied irrespective of the mode of distillation. It is merely neces¬ 
sary to conduct all distillations of pure acids and mixtures in the same 
manner. 
