New YorK AGRICULTURAL EXPERIMENT STATION. 203 
present in a sample of fresh milk; in a study of ripened cheese, 
it precipitated the uncrystallizable end-products, caseoses and 
peptones, so completely that no further trouble was experienced 
in separating the crystallizable end-products. 
It is well to record the fact here that, when precipitation of 
peptones with tannin-salt solution is attempted in a mineral acid 
solution, no precipitate occurs; it is only in neutral solution that 
more complete precipitation takes place. 
The chief objection to the use of tannin-salt solution as a 
means of separating caseoses and peptones from amido-acid com- 
pounds and ammonia is that it is not a complete precipitant of 
peptones. Hence, when we use the reagent for this separation, 
we commonly leave some peptones to be estimated as amido-acid 
compounds, the amount of peptones thus being made smaller, 
and the amount of amido-acid compounds larger, than the quan- 
tity actually present. Under our discussion of the use of phos- 
photungstic acid as a reagent for separating these classes of 
nitrogen compounds, we will give for comparison some results 
secured by each of the two reagents. 
(2) By phosphotungstic acid with sulphuric acid.— In a 250 
ce. graduated flask we place 100 cc. of the water-extract of 
cheese, add 100 ce. of water and then 5 cc. of strong sulphuric 
acid. To this we add phosphotungstic acid of 30 per ct. strength 
until one drop gives no further precipitation in the clear super- 
natant liquid. We then dilute to the 250 cc. mark and filter 
through a dry filter. In 50 ce. or 100 ce. of this filtrate we deter- 
mine the amount of nitrogen by the Kjeldahl method and then 
the amount of peptones is obtained by difference. 
Phosphotungstic acid has come into very general use in this 
country and in Europe as a means of separating peptones from 
amido-acid compounds in work with cheese and milk. The work 
of Stutzer™ and of Bondzynski” agrees in showing that phos- 
photungstic acid is a complete precipitant of casein, caseoses 
and peptones, while in their experience it does not precipitate the 
amido-acid compounds or ammonia. Freudenreich and Jensen 
in all their work, even of recent date, have used this reagent in 
11 Zeit. f. Analyt. Chem., 35: 493 (1896). 
12Q.andw. Jahrbuch der Schweiz (1894). 
