202 REPORT OF THE CHEMIST OF THE 
sodium chloride, (2) phosphotungstic acid with sulphuric acid, 
and (8) bromine with hydrochloric acid. After the removal of 
peptones, the filtrate contains amido-acid and ammonia com- 
pounds. After determining the amount of total nitrogen in this 
filtrate and then the amount of nitrogen present in the form of 
ammonia, as obtained in 10, p. 211, we subtract the amount of 
annnonia nitrogen from the combined amount of amido-acid and 
ammonia nitrogen and thus obtain the amount of amido-acid 
nitrogen. In the following section (9) we describe the methods 
involved in removing peptones by the different reagents, and the 
efficiency of each reagent. 
9, DETERMINATION OF NITROGEN IN THE FORM OF PEPTONES. 
(1) By tannin and sodium chloride-—We place 100 ce. of our 
water-extract of cheese in a 250 cc. graduated flask, add 1 gram 
of sodium chloride and a solution containing 12 per ct. of tannin, 
intil one drop added to the clear supernatant liquid gives no 
further precipitate. We then dilute to the 250 cc. mark, shake, 
filter through a dry filter and determine the amount of nitrogen 
in 50 cc. of the filtrate by the Kjeldahl method; this gives us the 
amount of nitrogen in the form of amido-acid and ammonia com- 
pounds. The amount of nitrogen in the form of peptones is 
determined by difference, that is, by subtracting from the amount 
of total nitrogen in the water-extract the combined sum of the 
amounts of nitrogen found in 5, 6, 7, 8 and 10. 
The combination of tannin and salt has been settled upon by 
us as the most satisfactory for the separation of casein-derived 
peptones from amido-acid compounds in milk and _ cheese 
analysis, when, as is commonly the case, we have large amounts 
of amido-acid compounds relative to peptones. We have con- 
firmed Schjerning’s’ results showing that this reagent does not 
precipitate the monoamido-acid compounds, such as_ leucine, 
tyrosine, aspartic acid, glumatic acid and amidovaleric acid, nor 
does it precipitate histidine, arginine, lysine, cadaverine, putre- 
Scine, lysatine or ammonia. In our work the tannin-salt solution 
has nearly as great a precipitating power as phosphotungstic 
acid, precipitating 93.3 per ct. of the total nitrogen compounds 
Zeit. f. Analyt. Chem., 39: 545 (1900). 
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