24-2 M U M US H U-MOt .i:-X . 



The Insoluble Humic Acid and the Humin Groups have so 

 far defied all attempts at chemical analysis, but from the other 

 two groups at least 20 distinct compounds have been isolated, of 

 whicJi only one is a carbohydrate. Is the absence of carbohy- 

 drates due to the fact that humus is the product of the breaking 

 down of carbohydrates in the soil ? Looked at side by side with 

 the fact that carbohydrates on acid decomposition }ield artificial 

 humus, there is a great deal to say for that view. 



It has long been known that substances akin to the humic 

 acid and humin groups are formed when sugars are heated with 

 solutions of mineral acids. According to (10) Bottomley, how- 

 ever, no humin is produced if the action of the acid is not allowed 

 to go too far ; humic acid alone is first formed when l?evulose, dex- 

 trose, and sucrose are heated with 3 /^ hydrochloric acid ; but if 

 the boiling is continued long enough, much humin will be formed. 

 Further, freshly precipitated humic acid is readily converted into 

 humin on boiling with acids. It would therefore ajjpear that 

 humic acid is a stage in the conversion of sugars, by 1)oiling with 

 acids, into humin. both humic acid and humin being used in the 

 group sense. 



In appearance and in solubility in alkaline solutions the 

 natural and artificial humic acid gnnips are very similar, yet when 

 analysed they differ very much. 



(11) Robertson, Irvine, and Dobson. state that the average 

 com])osition of both products is as follows: 



Carbon Hydrogen Oxygen 

 Artificial Humic Acid (sugar).. 64.747^ 4-^97^ 29.81% 

 Natural Humic Acid ( ])eat ) .. 54.297^ 4-947^ 38.16% 



They concluded that structural differences must exist between 

 the two substances. 



Van Bemmelen (1888) estaljlishcd the colloidal nature of 

 humic acid, while (12) Baiunann and ( iulley described its proper- 

 ties in 1909 in much greater detail, including its ])ower to decom- 

 pose salts, and the facility with which it forms adsorbtion com- 

 poimds. In view of the latter property, and in view of the fact 

 that, if natural humic acid is formed from carl)()h\(lrates. it is 

 formed in association with many adsurbablc substances, it ap- 

 peared likely that the difference in composition between it and 

 artificial humic acid might be due to adsorbtion by the nattiral 

 material. In urder to test this view Bottomley prepared some 

 humic acid from peat. He extracted a portion of this with alco- 

 hol to remove supposedly alcohol soluble substances. Chemical 

 analysis then gave the following results : 



Carbon Hydrogen Oxygen 



Natural llunuc Acid 48.64% 4-55% 46.81% 



Ditto ( ])urilie(l by alcohol ) .. 60.37% 5-39% 34-24% 



The latter results bear close resemblance to those obtained with 

 Robertson, Irvine, and Dobson. while thev arc almost identical 



