INSOLUBILITY OF HUMUS. 129 



solving a hundred-thousandth part of its own weight 

 of humic acid or humate of lime, and humic acid 

 were present, we should find the inner surface of the 

 roofs of these vaults and caverns covered with these 

 substances ; but we cannot detect the smallest trace 

 of them. There could scarcely be found a more 

 clear and convincing proof of the absence of the 

 humic acid of chemists in common vegetable mould. 



The common view, which has been adopted re- 

 specting the modus operandi of humic acid, does 

 not afford any explanation of the following phenom- 

 enon : — A very small quantity of humic acid dis- 

 solved in water gives it a yellow or brown color. 

 Hence it would be supposed that a soil would be 

 more fruitful in proportion as it was capable of giv- 

 ing this color to water, that is, of yielding it humic 

 acid. But it is very remarkable that plants do not 

 thrive in such a soil, and that all manure must have 

 lost this property before it can exercise a favorable 

 influence upon their vegetation. Water from barren 

 peat soils and marshy meadows, upon which few 

 plants flourish, contains much of this humic acid ; but 

 all agriculturists and gardeners agree that the most 

 suitable and best manure for plants is that which 

 has completely lost the property of giving a color 

 to water. 



•The soluble substance, which gives to w^ater a 

 brown color, is a product of the putrefaction of all 

 animal and vegetable matters ; its formation is an 

 evidence that there is not oxygen sufficient to begin, 

 or at least to complete the decay. The brown 

 solutions containing this substance are decolorized 

 in the air by absorbing oxygen, and a black coaly 

 matter precipitates — the substance named "coal of 

 humus." Now if a soil were impregnated with this 

 matter, the eff*ect on the roots of plants w^ould be 

 the same as that of entirely depriving the soil of 

 oxygen ; plants would be as little able to grow in 

 such ground as they would if hydrated protoxide 

 of iron were mixed with the soil. Indeed, some 



