210 Report oF tHE CHEMIST OF THE 
with the water-extract. In the case of one cheese two years old, 
the cheese extract, consisting of caseoses, peptones, and amido- 
acid compounds, contained nitrogen equivalent to 2.74 per ct. of 
the cheese before adding bromine, while, after standing one hour 
in contact with bromine in hydrochloric acid solution, there 
remained only 1.52 per ct. of nitrogen; in other words, there had 
disappeared 44.6 per et. of the nitrogen present before the addi- 
tion of bromine. In cheese one year old we have found the loss 
varying from nothing in one case to over 5 per ct. in others. 
To show whether or not this loss came from the action of bro- 
mine on the caseoses or peptones, we removed the caseoses with 
zinc sulphate and, in another sample of cheese extract, we 
removed the caseoses and peptones with phosphotungstie acid 
and the loss still occurred. By passing a current of air through 
the above extract in contact with bromine and then through 
potassium hydroxide and through sulphuric acid, these reagents 
were found free from nitrogen compounds, indicating that the 
lost nitrogen disappeared in the form of free nitrogen and not in 
the form of ammonia or nitrogen oxides. We cannot regard the 
method of determining the amount of peptones in cheese extracts 
by means of bromine as a reliable method; because, first, bromine 
precipitates small amounts of tyrosine and perhaps certain other 
similar compounds; second, it is not a complete precipitant of 
caseoses and peptones; and, third, its filtrate cannot be used for 
the determination of amido-acid compounds, especially in old 
cheeses, owing to the decomposing effect of bromine upon such 
compounds, setting nitrogen free. In addition, bromine is a 
most disagreeable reagent to handle. 
(4) Comparative value of different reagents used in separating 
peptones and amido-acid compounds.—We have now considered in 
some detail each of the three reagents most commonly used in 
separating peptones from amido-acid compounds, viz: (1) Tannin- 
salt solution, (2) phosphotungstic acid with sulphuric acid, and 
(5) bromine with hydrochloric acid. Tannin and salt solution 
fails as a perfect reagent for the separation, because it does not 
completely precipitate peptones, which results in making the 
quantitative results for amido-acid compounds too high and may 
indicate the presence of considerable quantities of amido com- 
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