INSOLUBILITY OF HUMUS. 



acid were present, we should find the inner surface of the roofs 

 of these vaults and caverns covered with these substances ; bu/ 

 we cannot detect the smallest trace of them. We must feel con- 

 vinced that humic acid is absent both from the soils of fields and 

 of gardens, when we consider that humic acid gives to water a 

 dark brown color, whereas well and spring water is quite clear 

 and colorless, and leaves after evaporation only a residue of salts 

 formed by mineral acids, without humic acid. The water of 

 wells and of springs is actually rain-water which, in passing 

 through the soil, must exert all its solvent action on the humates. 

 If humate of potash existed in soils, all the spring and river water 

 collected at a certain depth ought to contain traces of it. But 

 even the mineral waters from the springs of Selter and Fachin- 

 ger, containing alkaline carbonates, are destitute of a trace of 

 humic acid ; although these waters arise in a marshy soil abound- 

 ing in vegetable matter. There could scarcely be found more 

 clear and convincing proofs of the absence of the humic acid of 

 chemists from common vegetable mould. 



The common view adopted respecting the modus operandi of 

 humic acid does not afford any explanation of the following phe- 

 nomenon : — A very small quantity of humic acid dissolved in 

 water gives to 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 giving this color to water, that is, of yielding it 

 humic acid. But it is very remarkable that cultivated 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 cultivated plants is that which has 

 completely lost the property of giving a color to water. 



The soluble substance, which gives to water a brown color, is 

 a product of the putrefaction of all animal and vegetable mat- 

 ters ; its formation is an evidence that there is not oxygen suffi 

 cient 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 sub* 



