6 BULLETIN 158^ U. S. DEPARTMENT OF AGEICULTUEE. 
It should also be stated that although the results from the Van 
Slyke analysis are expressed m the usual way, arginuie N, histidnie 
N, etc., that it is not intended to convey the impression that these 
fractions contain pure arginine, histidme, etc., since as will be shown 
later, other compounds are included under these analytical terms. 
However, the nitrogen so expressed is that which is contained in 
compounds "which give the various reactions upon which the Van 
Slyke method depends. 
Two 20-gram samples of base goods were extracted for analysis. 
The first sample was extracted with boihng water until the extract 
ceased to give an acid reaction. The second sample was boiled for 
24 hours with hydrochloric acid, sp. gr. 1.115, the resulting solution 
was filtered by suction and the insoluble residue washed with hot 
water until the washings ran free from chlorides. The two extracts 
were then concentrated to the consistency of a sirup in vacuo to expel 
the- free volatile acid, and each was fijially made up to a volume of 
250 c. c. 
Total nitrogen. — Total nitrogen in solution was determined by sub- 
jecting 50 c. c. of the solution to Kjeldahl analysis. The water ex- 
tract contained 1.372 per cent and the hydrochloric-acid extract 1.435 
per cent of the base goods. 
Amide nitrogen. — Amide nitrogen was determined by distilhng in 
vacuo the remaining 200 c. c. of solution, to which were added 100 c. c. 
of 95 per cent alcohol and 20 c. c. of a 10 per cent suspension of cal- 
cium hydroxide, as described under the determination of ammonia. 
The water extract contained 0.374 per cent and the hydrochloric acid 
extract 0.882 per cent. 
Humin nitrogen. — The residue from the amide nitrogen determina- 
tion was used for the determination of humin nitrogen. The precipi- 
tate, formed by the addition of calcium hydroxide, was filtered off and 
washed with distilled water in the same manner in which Van Slyke 
directs that the phosphotungstic acid precipitate be washed. The 
washing was continued until no reaction for chlorides or alkalinity 
was obtained. The nitrogen remaining in the precipitate and in the 
filter paper was then determined by Kjeldahl analysis. The humin 
nitrogen was 0.031 per cent for the water extract and 0.074 per cent 
for the hydrochloric acid extract. 
Diamino acid nitrogen. — The combined filtrate and washings from 
the humin precipitate were neutrahzed with hydrochloric acid, con- 
centrated in vacuo to a volume of about 100 c. c. and then transferred 
to a 300 c. c. Erlenmeyer flask. To tliis solution were added 18 c. c. of 
concentrated hydrochloric acid together with 15 grams of purified 
phosphotungstic acid ^ and the whole diluted with water to a volume 
of 200 c. c. The flask was placed on a steam bath and heated until 
1 Winterstein, Zeit. physiol. Chem., 34, 153 (1901). 
