62 



III. DISCUSSION. 



A. Changes in nitrogen distribution in a protein when hydro- 

 lyzed in the presence of a mineral soil. From a study of Table 

 III it is seen that the histidine nitrogen formed when fibrin is 

 hydrolyzed alone is 4.36 per cent and when hydrolyzed in the pres- 

 ence of cellulose it is 4.86 per cent of the total nitrogen. By re- 

 ferring to Table II where fibrin is hydrolyzed in the presence of 

 ignited subsoil we see the histidine nitrogen is entirely lacking a.nd 

 that the nitrogen precipitated by calcium hydroxide amounts to 

 4.81 per cent. This corresponds very closely to the amount of 

 histidine found in the other two cases. In other points the three 

 analyses agree within experimental error. 



It appeared possible that the histidine nitrogen might have 

 been converted into the nitrogen fraction precipitated by calcium 

 hydroxide. It is a well known fact that histidine can be precipi- 

 tated by silver nitrate in slightly alkaline solutions. Since .there 

 are a large number of mineral constituents in the soil it may be 

 possible that the histidine could be precipitated by some of these 

 and thus be found with the calcium hydroxide precipitate. 



With this idea in mind an analysis of histidine was made in 

 the presence of an ignited subsoil, only three fractions being de- 

 termined. One 0.5000 gram sample of histidine di-hydrochloride* 

 and 50 grams ignited subsoil were boiled in the presence of 100 

 cc. of hydrochloric acid (sp. gr. 1.18) for 48 hours. The solution 

 was diluted to 500 cc. in a graduated flask and two 200 cc. portions 

 syphoned ofif and analyzed. The solution was deep straw color. 

 The determinations for ammonia nitrogen gave negative results. 

 The precipitate formed by calcium hydroxide was washed by de- 

 cantation until free of dissolved nitrogen compounds, and the total 

 nitrogen determined. This precipitate was bulky due to the pres- 

 ence of large amounts of ferric and aluminum hydroxides. The 

 average humin nitrogen in the two samples was only 0.0006 gram. 



The filtrate from the calcium hydroxide precipitate was con- 

 centrated to a small volume and the entire solution used for the 

 nitrogen determination. Sample I, contained 0.0371 gram in the 

 filtrate, and Sample II, 0.0365 gram, making an average of 0.0368 

 gram. 



The residual soil was practically colorless, and a determina- 

 tion indicated that it was nitrogen free. The volume occupied by 

 the soil residue was 17.3 cc. By calculation it was found that the 

 total nitrogen regained in the original solution was 0.0903 gram, 

 theoretical 0.0921 gram, or a recovery of 98.01 per cent. 



Thus practically all of the histidine was recovered in the fil- 

 trate from the calcium hydroxide precipitate, indicating that the 

 hypothesis was incorrect. 



*The histidine di-hydrochloride was prepared from dried blood as out- 

 lined by Abderhalden (1910). Total nitrogen found 18.42 per cent; calculated 

 18.42 per cent. 



