64 



of the histidine was converted into humin but was all recoverable 

 in the bases. I have shown that histidine is practically all recov- 

 ered in the nitrate from the humin when it is hydrolyzed in the 

 presence of an ignited mineral subsoil. Histidine, therefore, can 

 be eliminated as a factor in the formation of humin nitrogen in the 

 soil. Gortner and Blish conclude that 



in all probability the humin nitrogen or protein hydrolysis has its origin in 

 the tryptophane nucleus. 



Gortner (1916 c) has shown that the humin nitrogen is in- 

 creased by the addition of carbohydrate material to protein, and 

 suggests that this increase may be due to both physical and chem- 

 ical causes.* He presents evidence to show that the action of car- 

 bohydrate is probably due to the furfural produced from the car- 

 bohydrate and shows that increasing quantities of furfural cause 

 the humin nitrogen to steadily increase, and the work of Gortner 

 and Holm (1917) shows that the presence of formaldehyde during 

 hydrolysis causes a gradual increase in the amount of humin nitro- 

 gen up to a maximum very much larger than the amount of normal 

 humin nitrogen, and then a decrease with increased amounts of 

 aldehyde. 



Shmook (1914) states that during the hydrolysis of his soils 

 there separated on the walls of the condenser a substance violet blue 

 in color, and that this appears during the hydrolysis of pure pro- 

 tein an$ is recognized as Liebermann's reaction for protein sub- 

 stances. The above conclusion in regard to the hydrolysis of a 

 pure protein is incorrect, since no color appears on the neck of the 

 flask or condenser in such an analysis. When furfural is heated 

 alone with hydrochloric acid a characteristic colored substance is 

 deposited on the condenser. It has been shown by Gortner (1916 

 c) that at the same time a polymerization ( ?) of furfural to humin 

 takes place very rapidly. He found that when, 1.165 grams of 

 furfural were heated with 100 cc. of hydrochloric acid (sp. gr. 

 1.115) for 18 hours that 76.40 per cent of the original furfural was 

 converted into insoluble "humin." Our mineral soils on hydrolysis 

 gave a deposit on the condenser similar to that described by 

 Shmook. The reaction indicates the presence of furfural, which 

 is in turn formed from the carbohydrates in the soil. This must 

 be considered to be a distinctive furfural reaction. 



The humin nitrogen actually present in the soil may easily be 

 a very small part o-f the nitrogen found. It is evident that there 

 must be many nitrogenous organic compounds present in the soil 

 which have no relation to protein material, such as pu'rine, pyrimi- 

 dine bases, nitrogenous lipins, and nitrogenous pigments besides 

 a number of other non-protein substances. It is certain that the 

 humin nitrogen will be greatly changed by the presence of many 

 of these compounds. The calcium hydroxide here drags down all 

 the organic nitrogenous compounds which are soluble in dilute 

 acids, but insoluble in hot water and dilute calcium hydroxide, to- 



*Practically the same increase in humin nitrogen occured when fibrin 

 was hydrolyzed in the presence of a mineral subsoil. The humin in this 

 case was not due to the presence of carbohydrate since the soil had lost all of 

 its organic matter by ignition. 



