Intelligence and Miscella?teoiis Articles. 481 



ON HUMUS. BY M. SOUBEIUAN. 



It Is well known that old trees are met with in forests the trunk 

 of which decomposes slowly internally, and eventually becomes a 

 brown-coloured powder of greater or less intensity. When this de- 

 composition is much advanced, a moderately strong blow is sufficient 

 to occasion this product of decomposition to fall in abundance. The 

 author collected the altered wood which served for his experiments 

 from an old oak, which had a large hole low down, level with the soil. 

 It was moist; its colour that of Spanish snufF; its properties were 

 those of the purest mould. It was insipid and inodorous ; it yielded 

 no colour to water, and gave a deep-coloured solution with am- 

 monia ; treated afterwards with an acid, and then again by ammonia, 

 it was coloured. Lastly, this old wood, thus exhausted, soon again 

 gave another coloured liquor by contact with the air and alka- 

 lies. The powder of the old wood therefore consisted of a mixture 

 of pure humus, a little humate of lime, and a substance not yet 

 altered, but capable of being changed into humus by contact with 

 the air and alkalies. 



The author extracted the humus from this old wood by washing 

 it at first with water, and then treating it with ammonia. This so- 

 lution was precipitated by hydrochloric acid, and the humus purified 

 by repeated washings with water, boiling alcohol and aether. It was 

 then analysed. It left 7*16 per cent, of ash. By Varrentrapp and 

 Will's process, it yielded 2*5 per cent, of nitrogen. Deducting the 

 ash, combustion by oxide of copper and chlorate of potash gave — 



Carbon 55*0 



Hydrogen 4*8 



Nitrogen 2*5 



Oxygen 37*7 



100-0 



Subtracting the nitrogen, these numbers approximate C^^H'^ O". 



It is worthy of remark, that in this humus, formed by exposure 

 to air and moisture for many years, the carbon did not exceed 55 

 per cent. It seems that this is the extreme limit of the decomposi- 

 tion which lignine can undergo unassisted by heat and the concen- 

 trated alkalies. This limit, it will be observed, is far removed from 

 that assigned by M. Peligot to artificial ulmin, or 72 per cent. 



As to the nitrogen, which is always one of the constituents of 

 humus, it is impossible to say what proportion belongs to it, 

 and what proportion enters into the nitrogenous products, which 

 are mixed with it. It is to be observed, that, in the powder 

 of oak used, the quantity of nitrogen is greater than in the wood 

 which gave rise to it. This fact renders it probable that some of 

 the nitrogen of the air is fixed in it during the decomposition of the 

 wood ; this was the opinion of Theodore de Saussure. It may be 

 argued, that the remains of insects have supplied it ; but for a long 

 period this powder could have afforded them no shelter, since the 

 slightest shock causes it to fall at the foot of the tree. — Journ. de 

 Pharm. et de Chim., Mai 1850. 



