New York AGRICULTURAL EXPERIMENT STATION. 211 
in contact with either acid or alkali. The final filtration and wash- 
ing are completed on a Buchner funnel, the precipitate being 
washed until free from acid. The washed precipitate is then sus- 
pended in one liter of N-1000 HCl and agitated for two hours, 
in order to remove any remaining inorganic salts as completely as 
possible. Two treatments of this kind are given. The casein is 
finally washed until free from hydrochloric acid and is then agitated 
for two or three hours with a liter of very pure water (showing 
a conductivity not greater than 1.5 to 1.8 X 10-®), the operation 
being repeated two or three times until the filtrate shows an in- 
crease of not more than I or 2 X 10-® in conductivity, as com- 
pared with the conductivity of the wash water used. The pre- 
cipitate is then treated with about a liter of strong alcohol and 
ether (these reagents should show no conductivity when mixed 
with pure water), in order to remove any fat that may adhere 
to the casein. The precipitate is then dried at room temperature, 
ground fine in a mortar and finally dried at 45° to 50° C., until the 
moisture content is reduced to 3 or 4 per ct. Casein thus prepared 
by us had an ash content of about 0.25 to 0.30 per ct. We used this 
method of drying, because, according to Laqueur and Sackur,’ 
moisture can be completely removed from casein only by heating 
to a temperature that may alter the nature of the proteid. Cor- 
rection is made for moisture, so that the amounts used in our work 
represent water-free casein. 
It is important that the casein, when suspended in water, shall 
show little or no conductivity. With sufficient care one can prepare 
casein that is practically conductivity-free. Hardy? speaks of the 
impossibility of obtaining suspensions of globulin free from con- 
ductivity. 
The thorough treatment of the casein with dilute hydrochloric 
acid and water near the end of the process of preparation rendered 
it probable that no salts would be left in the casein in a form 
capable of vitiating results by dissolving or reacting with the acids 
used under the conditions of experiment. Proof of this was 
afforded by the agreement of the conductivity and titration results 
in experiments made under conditions such that solution of proteid 
