New York AGRICULTURAL EXPERIMENT STATION. 209 
ucts formed by the peptic digestion of egg-albumin and they 
developed the method practically as given above. As applied 
to the separation of peptones from amido-acid compounds in 
cheese and milk, the method gives varying results, depending 
upon the age of the cheese or milk used. 
In the case of our water-extracts made from cheese, nine 
months to a year old, crystalline bodies in noticeable quantities 
are precipitated by bromine along the peptones, due probably 
to the presence of tyrosine, giving the solution a turbid appear- 
ance and rendering filtration difficult. Schjerning! has shown 
that tyrosine behaves in this manner with bromine water. This 
precipitate is partly retained on the filter paper and is esti- 
mated as peptone. | 
Schjerning has shown also that bromine does not completely 
precipitate milk-proteids and their derived caseoses and pep- 
tones. Of the whole proteid, he obtained only 76.7 per cent. by 
bromine. In the case of milk, we have obtained results vary- 
ing with the age of the milk. ‘In perfectly fresh milk, when the 
amount of amido compounds must have been least, we obtained 
91.3 per cent. of the entire milk proteids by bromine precipita- 
tion. In another case of fresh milk, we compared the precipi- 
tation of proteids by bromine and hydrochloric acid with that 
by tannin and sodium chloride and by solution of phospho- 
tungstic acid and sulphuric acid, with the following results: 
Percentage of 
Precipitated by— total nitrogen 
Phosphotungstic. and sulphuric acids.............-..+.- 93.8 
Pamoanieand: SOdIUM CHIOTIAC a6 severe + sini, cisige LAB Rineous alte 93.3 
Peano snTid N VOTOCH OTIC, ACIG scotia acing © Lele wate ole laae ss 91.5 


There is also a possible source of error in connection with the _ 
use of bromine in precipitating peptones, when the filtrate from 
the bromine precipitate is used directly for the determination of 
amido-acid compounds. We have found in the case of water- 
extracts from cheese over one year old that there is an actual 
loss of nitrogen when bromine is allowed to stand in contact 
19Zeit. f. Analyt. Chem. 39: 545 (1900). 
14 
