New York AGRICULTURAL EXPERIMENT STATION. 243 
rennet, is treated with varying amounts of acid, the amount of » 
salt-soluble substance did not increase until a certain amount of 
acid had been used, after which it increased quite out of propor- 
tion to the increased amount of acid used. It was suggested that 
the formation of the salt-soluble compound did not begin until 
certain inorganic salts of the milk had been neutralized. 
After developing the later facts described above, we proposed 
to study more fully the following questions: 
1. What is the relation between milk-casein and the salt- 
soluble compound which we called a casein mono-salt? 
2. What is the relation between the two series of compounds 
previously called casein mono-salts and casein di-salts? 
3. What is the relation of casein and its derivatives to para- 
casein and its derivatives? 
It may be well to state here, once for all, that our work deals 
exclusively with the casein of cows’ milk and products derived 
from it. 
THE RELATION OF MILK-CASEIN TO THE CASEIN COM- 
POUND SOLUBLE IN DILUTE SALT SOLUTIONS. 
A study of the relation of milk-casein to the salt-soluble sub- 
stance, which we have previously called a casein mono-salt, 
naturally resolves itself into a study of the two following ques- 
tions: (1) What is milk-casein, especially in relation to inor- 
ganic compounds? and (2) What is the salt-soluble compound 
formed from milk-cagein? 
THE RELATION OF INORGANIC COMPOUNDS TO MILK-CASEIN, 
Does casein, as it is found in cows’ milk, exist as a free proteid 
or is it in some form of combination with an inorganic compound? 
Hammarsten, who must be regarded as the most successful 
pioneer worker in this field, has not clearly and specifically stated 
what he considers milk-casein to be. He does not appear to make 
any chemical distinction between ash-free casein, as prepared 
from. cows’ milk by his well-known method, and casein as it is 
found in milk. He appears to favor the idea that there is in milk- 
casein some kind of a physical relation between the proteid and 
calcium phosphate, casein acting as a solvent for calcium phos- 
