90 ReEeporT OF THE CHEMIST OF THE 
reports finding 0.8 per ct. of lactic acid in sour milk, a figure 
that is quite close to the results of our work. 
(3) Relation of coagulation of milk to amount of acid.—In the 
case of experiment No. 3, the milk was found completely coagu- 
lated, that is, solidfied in a mass, in 26 hours, when the amount 
of tot'al acid had reached 0.783 per ct. In experiment No. 4, 
the time of coagulation was 24 hours and the percentage of total 
acid was 0.963. The milk in No. 2 had just coagulated when 
the acidity of the whey was determined and it had the charac- 
teristic odor of sour milk. A microscopic examination showed 
the presence of a precipitate, but no free acid was indicated by 
the calcium picrate test.17 In the case of experiments No. 1, 
and No. 4 the milk coagulated in the night and our observation 
was made in the morning, just how long after coagulation we do 
not know. Under the ordinary conditions of souring, we can 
expect, according to these results, that milk will coagulate when 
the total acid reaches about 0.8 to 0.9 per ect. as indicated by 
titration with standard alkali and phenolphthalein as indicator. 
Deducting the amount of the original titration of the fresh milk, 
and calling the rest lactic acid, we have coagulation taking place 
when the lactic acid reaches 0.6 to 0.7 per ct. In producing 
this amount of lactic acid, about 1.3 per ct. of milk-sugar dis- 
appears, which is about 25 per ct. of the sugar originally present 
in the milk used. 
(4) Soluble nitrogen compounds.—The soluble nitrogen com- 
pounds amounted to about 22 per ct. of the nitrogen in the milk. 
This is practically all accounted for by the milk-albumin. The 
constancy of the amount of soluble nitrogen also suggests that 
it was present mostly if not entirely, as milk-albumin. 
(5) Formation of casein monolactate and casein dilactate in 
milk coagulated by ordinary souring.—When the milk was first 
visibly coagulated, the amount of casein in the form of mono- 
lactate was 13 to 14 per ct. of the casein in the milk and the 
amount of casein dilactate was'86 to 87 per ct. of the casein 
in the milk. As the milk grew more acid, the monolactate grad- 
ually passed into the dilactate. The minute amount of mono- 
lactate apparently present at the time the experiment was stopped 
is due to a slight solubility of dilactate in a 5 per ct. salt 
solution. When milk coagulates by souring in the usual way, 
“Rohrer. Archiv. f. Physiol., 90:368 (1902). 
