80 THAEll ON HUMIC ACID IN SOIL. 



" Humus" is the term used by this author for the decomposed 

 vegetable and other organic matter which is more or less mixed 

 with all surface soil, and which gives to soil all its fertility, and 

 furnishes all the food of plants. He continues : 



"It is the residue of animal and vegetable putrefaction, and is a black 

 body; when dry it is pulverulent, and when wet has a soft, greasy feel." 

 "It is the produce of organic power a compound of carbon, hydrogen, 

 nitrogen, and oxygen, such as cannot be chemically composed," &c. p. 534. 



" When humus remains constantly damp, without, however, being covered 

 with water, it forms a very unpleasant smelling acid, which is more parti- 

 cularly characterized by the property which it possesses of colouring blue 

 litmus paper into red. This* circumstance has long been known, and it is 

 the reason that land and meadows which are not properly drained, and 

 which exhibit these phenomena, are called sour. We have carefully exa- 

 mined these facts, and have endeavoured to discover the peculiar constitu- 

 tion of this acid. At first, we were inclined to regai-d it as being of a dis- 

 tinct nature, and having carbon for its base ; but we have since become 

 convinced that it is generally composed of acetic acid, and occasionally 

 contains a portion of the phosphoric. This latter always adheres so firmly 

 to the humus that it cannot be separated from it either by boiling or wash- 

 ing. The liquid in which the humus is boiled certainly acquires a slight 

 acid flavour, but the greater part of the acid remains attached to the hu- 

 mus." " This acid or sour humus is not at all of a fertilizing nature ; on the 

 contrary, it is prejudicial to vegetation.* Where it is very strong and per- 

 vades the whole of the humus, the soil only produces reeds, rushes, sedge, 

 and other useless, unpalatable plants ; and whenever these abound, it may 

 be inferred that the soil contains a great deal of sour or acid humus, "f 

 " There are various means of getting rid of this baneful property, and 

 rendering the humus fertile." "It is well known that with the aid of al- 

 kalies, ashes, lime, and marl, humus may be deprived of its acidity, and 

 rendered easily soluble." "Heaths do not thrive where this [acid] humus 

 does not exist, and when they have established themselves in one particular 

 spot, they suffer few other plants to appear. This humus may be changed 

 by a dressing composed of marl, lime, or ammonia ; and where this has 

 been mixed with the soil, the heaths, &c., speedily perish." (p. 538-9.) 



" In the greater number of cases, peat is very much like acid or sour 

 humus ; indeed, it sometimes resembles it so strikingly that it is impossible 

 to distinguish these substances apart." (p. 540.) 



"In both the kinds of land we have been considering [i. e., classes of 

 very fertile soil, rich in humus], we have supposed the humus to be mild, or 

 exempt from acidity. J Sour or acid humus totally destroys the fertility of a 

 soil; sometimes, however, the soil contains so very small a portion of acid- 

 ity that its fertility is very slightly diminished, and only with regard to 

 some few plants. Barley crops become more and more scanty in propor- 

 tion as the acidity is increased ; but oats do not appear to be at all affected 

 b} T it. Rye grown on such land is peculiarly liable to rust, and is easily 

 laid or lodged. The grains of all the cereals become larger, btft contain 



* Even to this day, Von Thaer is the only agricultural chemist known, 

 who affirms, with me, this important evil quality of the acid of soil. E. R. 



| These, of course, are like our broom-grass, sorrel, poverty grass, pine, 

 &c.,'of the general class of what I called acid plants. Heath is another, 

 and the most abundant in Europe, though not existing in America. E. R. 



J Which, according to my vtfcws and language, would be expressed by the 

 actd of the soil having been neutralized by lime. E. II. 



