368 Chittenden and Painter— Casein and its 
the hydrochloric acid being 0-2 per cent. In dissolving the casein 
for re-precipitation, a very dilute solution of ammonium hydrox- 
ide was employed; in fact so dilute as to consist of hardly more than 
water with a trace of ammonia. We used ammonia, in preference to 
sodium or potassium hydroxide, as this alkali would seem less liable 
to induce any alteration in the content of sulphur. Further, in dis- 
solving the casein in ammonia, the solution at no time became more 
than very faintly, if at all alkaline; usually being hardly more than 
neutral to test papers. 
The general method of procedure was to dilute fresh cow’s milk 
with about four volumes of water (skimmed milk diluted considerably 
less) and then to precipitate the casein with either hydrochloric or 
acetic acids, adding the precipitant cautiously, until complete precipi- 
tation was obtained. The precipitate was then washed as completely 
as possible with large quantities of water, both by decantation, tritura- 
tion with water in a mortar and on a cloth filter. The casein was 
then dissolved in the ammonia water, filtered through paper and 
reprecipitated, each time being thoroughly washed with water. In 
the portion used for analysis, the final precipitate was further washed 
with alcohol and ether and lastly soaked in a mixture of alcohol and 
ether for the more complete removal of any fat. The preparations 
were then dried in the air and lastly on a water bath at a gentle heat. 
When dry, they were powdered and extracted with boiling ether 
in a fat extractor for several hours, to insure complete freedom 
from fat. Ultimately, the products for analysis were dried at 105° C. 
in vacuo until of constant weight. 
In all, seven preparations of casein were made for analysis, as 
follows: 
No. I. From fresh milk, precipitated twice with hydrochloric acid. 
‘© TI. From fresh milk, precipitated twice with acetic acid. 
«* JII. From skimmed milk, precipitated three times with acetic acid. 
«« TV. A portion of No. III, precipitated a fourth time with acetic acid. 
«  V. From skimmed milk, precipitated three times with hydrochloric 
acid. 
« VI. A portion of No. V, precipitated a fourth time with hydrochloric 
acid. 
«* VII. From skimmed milk, precipitated four times with hydrochloric 
acid. 
The methods of analysis were essentially the same as those em- 
ployed by Kiihne and Chittenden in the analysis of the various albu- 
mose bodies. Carbon and hydrogen were determined by combus- 
