558 Non-Protein Nitrogen of Wheat Flour 
As nearly as may be ascertained from determinations with 
such small amounts of material as are necessitated in the pre- 
ceding experiments, the figures reported in Table III show that 
there cannot have been much, if any, protein left in solution 
after the first precipitation by the copper method. The amino 
nitrogen determinations on Solution X before and after precipi- 
tation with phosphotungstic acid show that there is 1.81 per 
cent less amino nitrogen after the precipitation than before. 
This must be due to the exposed amino groups of the nitrogenous 
matter precipitated by the phosphotungstic acid, and although 
the difference involved the measurement of only 0.03 cc. of 
nitrogen gas in the micro determination, it was confirmed by 
repeated determinations which agreed practically as closely as 
the burette could be read. After hydrolysis there was about 
eight times as much amino nitrogen, which clearly indicates that 
the precipitate consisted chiefly of peptides of a less complex 
nature than protein. The amino nitrogen in the filtrate from 
the treatment of Solution X with phosphotungstic acid which 
amounted to 4.81 per cent probably originated from the free 
amino-acids in the extract. There is a much larger discrepancy 
between the percentage of total nitrogen precipitated by phos- 
photungstic acid and the sum of the percentages of ammonia and 
amino nitrogen after hydrolysis than may reasonably be ac- 
counted for by the non-amino nitrogen of the peptide compounds. 
This seems to indicate that there are other basic nitrogen com- . 
pounds in flour extracts, whose nature is as yet largely unknown. 
A murexide test for purines resulted negatively. 
An attempt was made to ascertain whether or not the copper 
method removes along with the proteins any appreciable amounts 
of amino-acids or peptide-like compounds of a nature less com- — 
plex than that of the proteins by redissolving some of the cop- 
per-protein precipitate in glacial acetic acid and testing the solu- 
tion for free amino groups since the presence of considerable — 
copper does not interfere with the reaction between the amino 
‘groups of amino-acids and nitrous acid. Accordingly a solution 
of the copper precipitate containing 4 mg. of nitrogen was intro- 
duced into the Van Slyke micro-apparatus, but there was no 
evidence to show that any such compounds were present in the 
precipitate. Therefore, it is not believed that any serious error 
