86 ‘Report OF THE CHEMIST OF THE 
We are still engaged in a more complete study of the chemical 
relations of acids to casein, the final results of which will be 
published later. By our further study we have been able to pre- 
pare these compounds under more complete control. It is our 
purpose in this bulletin to present the results of some work done 
to show the amounts of the mono- and di-compounds of casein 
formed in the usual souring of milk, and also to consider these 
results in some of their practical applications. 
The manufacture of cottage, or Dutch, cheese is extensively 
carried on both on a large scale in connection with creameries 
and also on a small scale in private families. As this is a pro- 
duct of the souring of milk, it seemed to us desirable to make 
a careful study of the details of the process of making cottage 
cheese. We have paid attention in our work to the following 
points: 
(1) What compound of casein, the monolactate or dilactate, 
is most largely present in cottage cheese? 
(2) What conditions are most favorable for the production 
of the best cottage cheese? 
(3) Can cottage cheese be made successfully by the direct 
addition to milk of artificial acids? 
(4) Does ripening take place in cottage cheese, such as occurs 
in cheddar cheese? 
(5) What is the digestibility of cottage cheese in compari- 
son with cheddar cheese, as shown by artificial peptic digestion? 
EXPERIMENTAL PART. 
THE CHEMICAL CHANGES IN THE ORDINARY SOURING OF MILK. 
We desired to study the relation existing between the dis- 
appearance of milk-sugar in the usual souring of milk and the 
formation of lactic acid, together with the resulting formation of 
casein monolactate and casein dilactate. In one set of experi- 
ments made for this purpose, we placed some fresh separator 
skim-milk in an Erlenmeyer flask, stoppered with a plug of: cot- 
ton. This was allowed to stand at room temperature and samples 
were taken from this flask for examination from time to time. 
In the first experiment, the room temperature varied from 65° 
