HUMUS 75 



differences between the material and the artificial 

 Humic acids. Recent work, however, done by 

 Baumann in 1909 had shown that freshly precipi- 

 tated natural Humic acid possessed colloidal* prop- 

 erties, and especially the power of forming adsorption 

 compounds. Now these compounds can be removed 

 without much difficulty, and it seemed possible that 

 the differences observed between natural and arti- 

 ficial Humic acids might be due to impurities which 

 had been adsorbed by the Humic acid in the peat, 

 and which were not present in the artificially pro- 

 duced acid because it had had no opportunity of 

 ever becoming contaminated. It will be remembered 

 that it was the discrepancy noted between the weight 

 of the Nitrogen in the air and the Nitrogen prepared 

 by chemical methods which led Sir William Ramsay 

 to undertake the brilliant series of researches result- 

 ing eventually in the discovery of the rare gases of 

 the atmosphere. It will be seen later that the 

 study of the difference between natural and artificial 

 humic acids has led to conclusions of far greater 

 importance than had been suspected. 



Elaborate means were taken to purify the natur- 

 ally produced Humic acid. Some finely divided 

 peat was powdered and treated with 4 per cent. 

 Hydrochloric acid until all soluble salts had been 

 extracted, and then treated with 5 per cent. Am- 

 monia. The filtered Ammonia solution was acidified 



* A colloid is a substance possessing a very large molecule, 

 and, unlike most inorganic chemical compounds, is unable to 

 pass through an animal membrane. By adsorption is meant 

 the power possessed by colloids of holding other substances not 

 in actual combination with them, but in a very close association. 



