10 



A number of chemists have given the percentage composition 

 of the supposed acids, but no two agree. Nothing is known in re- 

 gard to their constitution. The lack of definite chemical character- 

 ization of these compounds is stated by Cameron and Bell (1905) 

 as follows : 



The existence itself of these acids has never been satisfactorily demon- 

 strated. * * * * No satisfactory description of the physical or chemical 

 properties of these supposed acids, their salts, or characteristic derivatives, 

 have been recorded. 



Nearly every writer on soils from the time of Mulder to Hil- 

 gard (1906, p. 126) spoke of these acids with the same assurance 

 as of oxalic or tartaric acids, or any other organic compound that 

 has well known derivatives. 



The early investigators, including Mulder, soon found that 

 sugar, starch, carbohydrates generally, and even proteins, when 

 treated with strong acids or alkalies, gave rise to dark colored 

 compounds having the same general appearance and properties 

 as the humus substances arising in the soil through decay. How- 

 ever, a conspicuous feature of the work on these humus substances 

 is the discordant results for preparations bearing the same name 

 and often from the same source. 



Robertson, Irvine, and Dobson (1907) reached conclusions that 

 although there were many strong resemblances between natural 

 and artificial humus preparations, in regard to properties and com- 

 position, yet there are important differences in constitution. Re- 

 cently Gortner (1916 c) has shown that in all probability the humin 

 formed from carbohydrates is actually formed by a polymerization 

 of furfural which is in turn formed from the carbohydrates by the 

 action of the acid. Gortner and Blish (1915), Gortner (1916 c), and 

 Gortner and Holm (1917) have likewise shown that the dark col- 

 ored products originating in an acid hydrolysis of protein sub- 

 stances have their origin in the tryptophane nucleus. Obviously, 

 if carbohydrate humin originates from furfural, and protein humins 

 originate in the tryptophane nucleus, mixtures of protein and 

 carbohydrate would produce a great variety of physically similar 

 but chemically different mixtures. 



One of the important points at issue between the early in- 

 vestigators was whether humic acid and allied bodies contained 

 nitrogen as a constituent. Mulder (1849, 1862) held that nitrogen 

 was not a constituent of these substances, but was present as 

 ammonia, that is the acids were present in the soil as ammonium 

 salts, and in this connection he says : 



In good arable soil that is, one in which the organic constituents are as 

 far as possible decomposed none of these substances contain nitrogen 

 as a constituent element; all their nitrogen exists in the state of ammonia. 



Detmer (1871) came to the opposite conclusion, claiming that 

 nitrogen in humic acid as usually obtained, was present in organic 

 combination (not, however, bound in the humic acid molecule). 

 He obtained his humus by digesting with alkali. After precipitat- 

 ing with acid, he redissolved it in ammonia and precipitated the 

 mineral constituents with phosphoric and oxalic acids and am- 

 monium sulphide. After treating with potassium hydroxide and 

 precipitating with hydrochloric acid, he obtained a preparation 



