92 BOTANICAL GAZETTE [FEBRUARY 
same quantity of the same acid was added to the blank determina- 
tion, so that subtracting the blank subtracted the sulphur added 
in the sulphuric acid as well as that present in the reagents. In 
every case the 1o cc. was measured between the 1o and 20 marks 
on the burette. According to Kocu, barium sulphate does not 
precipitate readily when the concentration of the SO, ion is low. 
The addition of the sulphuric acid is then necessary to bring the 
concentration of the SO, ion up to the point where precipitation 
takes place readily. The method as finally adopted is as follows: 
The equivalent of 10 gm. of oven dry soil was weighed into a 
nickel crucible, moistened with a few drops of distilled water, and 
part of a weighed 20 gm. of sodium peroxide stirred in a little at 
a time with a nickel tod: (If the moisture was just right, reaction 
took place immediately without the application of heat, and the 
charge was fairly dry by the time most of the sodium peroxide had 
been stirred in. If too little water had been added, it was neces- 
sary to heat with an alcohol lamp to start the reaction. If too 
much water was added, it was necessary to heat with the alcohol 
lamp to bring to the desired degree of dryness before adding the 
last of the sodium peroxide.) After the charge was fairly dry, the 
rest of the sodium peroxide was placed over the charge, the crucible 
covered, and heated over a bunsen burner, raising the temperature 
gradually to a fairly high temperature which was maintained for an 
hour. After cooling, the fused mass was removed with hot dis- 
tilled water to a 6oocc. beaker, neutralized with concentrated 
HCl, and then 1occ. additional concentrated HCl added. The 
beaker was then heated for five or six hours on the steam bath with 
occasional stirring. It was then transferred to a 5oocc. flask, 
covered, and made up to the mark. The solution was shaken 
frequently for several hours and the 250 cc. filtered off. The 
250 cc. of filtrate was transferred to a 600 cc. beaker, heated on 
the steam bath, and the iron, aluminium, and silica precipitated 
with ammonium hydroxide, allowed to stand a few minutes, and 
then filtered into a one liter beaker. The precipitate was washed 
with hot distilled water until the combined filtrate and washings 
had a volume of approximately 600 cc. Exactly ro cc. of approx- 
imately N/1o H,SO, was then added, heated to boiling, and ro cc. 
