New York AGRICULTURAL EXPERIMENT STATION. 201 
6. DETERMINATION OF NITROGEN IN THE FORM OF PROTEIDS COAGU- 
LABLE BY HEAT IN NEUTRAL SOLUTION. 
The filtrate from the preceding determination (5) is made neu- 
tral with dilute caustic potash, using phenolphthalein as an indi- 
cator. It is then heated at the temperature of boiling water, 
until any coagulum that forms settles completely, leaving a clear 
supernatant liquid. The precipitate is washed with water and 
its nitrogen determined by the Kjeldahl method. In our experi- 
ence such a precipitate rarely occurs, except in the case of cheese 
ripened near freezing point. The nature of this body we have not 
yet investigated. 
7. DETERMINATION OF NITROGEN IN THE FORM OF CASEOSES 
( ALBU MOSES. ) 
The filtrate from the preceding determination (6) is treated 
with 1 ec. of 50 per ct. sulphuric acid, saturated with c. p. zine 
sulphate and then warmed to about 158° F. (70° C.), until the 
caseoses separate completely and settle. The mixture is allowed 
to cool and is then filtered. If filtered hot, there will occur a 
further separation of caseoses in the filtrate on cooling. The 
precipitate is washed with a saturated solution of zinc sulphate 
made slightly acid with sulphuric acid. The nitrogen in the pre- 
cipitate is determined by the Kjeldahl method. 
For the determination of caseoses the use of ammonium sul- 
phate was exclusively employed, until Bémer® proposed the use 
of zinc sulphate, which possesses a distinct advantage in enabling 
one to determine nitrogen directly in the precipitate or filtrate. 
This method has been employed in the estimation of caseoses 
also by the Wisconsin Agricultural Experiment Station. In the 
present state of our knowledge of this class of compounds, zine 
sulphate must be regarded as the most available reagent for their 
quantitative separation. 
8. DETERMINATION OF NITROGEN IN THE FORM OF AMIDO-ACID 
COMPOUNDS. 
The amido-acid compounds are determined in the filtrate from 
the precipitation of peptones (9). For the removal of peptones 
three reagents have been commonly used—(1) Tannin and 
Zeit. f. Analyt. Chem., 5: 562 (1895). 
