New York AGRICULTURAL EXPERIMENT STATION. 251 
When the product made by neutralizing the lime-water solu- 
tions of ash-free casein with hydrochloric acid was dissolved in 
hot 50 per ct. alcohol, the dissolved proteid separated from the 
alcoholic solution on cooling, forming on the bottom of the 
beaker a gummy, sticky mass, which could easily be gathered on 
the end of a glass rod. When the body, freshly precipitated 
from its solution in lime-water, is warmed on the water-bath, it 
can similarly be easily gathered on a glass rod in an adherent 
gummy mass. When warm, it is plastic and can be drawn out 
in fine, long, silky threads. 
Identity of base-free casem and salt-soluble body.—In the pre- 
sentation of facts preceding, we have seen that when an ash-free, 
that is, base-free proteid, or one practically so, is prepared by 
precipitating milk-casein (calcium casein), with an acid, the acid 
precipitant being completely removed from the proteid, or by 
treating a lime-water solution of a base-free casein with an acid 
to the point of acidity with litmus, we obtain a body which 
is soluble in warm 5 per ct. salt solution and in hot 50 per ct. 
alcohol. This body, when freshly prepared and warmed, is very 
plastic and is capable of being drawn into very long, fine, silky 
threads. It behaves in all respects like the compound which we 
were led to regard at first as a compound formed by combination 
of casein and an acid, and which we regarded as a casein mono- 
salt of the acid precipitant. As a result of this work, we now 
believe that the compound formed by treating milk with an 
amount of acid just sufficient to combine with the calcium of the 
calcium casein, in addition to certain inorganic salts of the milk, 
is not a casein mono-salt of the acid but is base-free casein, or 
milk-casein (calcium casein) from which the calcium has been 
removed by combination with acid. 
THE RELATION BETWEEN THE TWO SERIES OF COM- 
POUNDS PREVIOUSLY CALLED CASEIN MONO-SALTS 
AND CASEIN DI-SALTS. 
We have already seen that when calcium casein (milk-casein) 
is treated with dilute acid, the base is removed from its combina- 
tion with the proteid and the base-free proteid is formed, a com- 
pound corresponding in its properties to those of the compounds 
we formerly called casein mono-salts of acids. When to this 
