
494 Report oF THE CHEMIST OF THE 
Statement of results.— First, when milk was kept at a tempera- 
ture of 17° to 22° C. for twenty-four hours, the amount of 
nitrogen as casein was found, in most cases, to be nearly 0.02 
per cent. less than in fresh milk. 
Second. In case of one milk kept seven days, the amount of 
nitrogen in the casein was 0.051 per cent. less than in fresh milk, 
while, in another case, it was 0.019 per cent. less. 
Third. In general, it was found necessary, in order to get 
results that were at all satisfactory, to use less than 1.5 cc. of 
dilute acetic acid to precipitate the casein in milk that had been 
standing long enough to undergo any marked change. 
Fourth. While good results may, in exceptional cases, be 
secured in determining casein in milk that has undergone notice- 
able change without any modification of the method given for 
the determination of casein in fresh milk, the accuracy of such 
determinations must be regarded as uncertain in regular work. 
(6) The influence of mercuric chloride used as a preservative 
on the determination of casein in milk.—In view of what has 
just preceded, can we be certain of our results when we deter- 
mine casein in milk that is not fresh? The thought suggested 
itself to the author that if some germicide could be added to 
fresh milk to prevent or retard the changes that affect the casein, 
then we might be able to determine the casein in milk that had 
stood indefinitely. In order to test the question, finely pow- 
dered mercuric chloride was used in proportion of about one 
part of mercuric chloride to 2,000 parts of milk by weight. 
A sample of milk was analyzed when fresh, and portions were 
set aside for varying periods of time, some with and some with- 
out the addition of mercuric chloride. Determinations of casein 
were made from time to time, using less than 1.5 cc. dilute acetic 
acid. The results were as follows: 

AGE OF MILK. 
ag 
Ooo 
bos 
Aa 
ro 
AS 
ex 
°2 
~~ 
aD 
8 & 
© 
oF 
no mercuric chlo- 
ride was used. 
Per cent. of nitrogen 
in precipitate when 
mercuric chloride 
was used. 
Amount of loss. 
Amount of loss. 

