246 HUMUS. 



obtained dissolves almost totally in water. The solution is of a very 

 deep brown color, and contains as principal ingredient ulmine com- 

 bined with potash ; the ulmine is precipitated by the addition of a 

 sufficient quantity of weak sulphuric acid. After having been 

 washed and dried, ulmine is black and brittle, and resembles jet ; 

 while still wet, it reddens turnsole paper, and its solution in potash 

 forms with several salts, and by the way of double decomposition, 

 insoluble ulmates. M. Peligot assigns to ulmine the following 

 composition : 



Carbon 72-3 



Hydrogen G.2 



Oxypen 21.5 



100.0 



Dunghills, rotten wood, and mould, always contain a brown sub- 

 stance, which possesses properties very similar to those which char- 

 acterize ulmine obtained by the action of alkalies upon ligneous 

 fibre. 



Mould which contains this ulmine in abundance, and in the con- 

 dition most favorable to vegetation, ought on that account to be 

 examined with attention. Its history has, indeed, been so ably traced 

 by M. de Saussure, that science at the j)resent day can add but little 

 to the important deductions of the celebrated author of the Re- 

 cherches Chimu/ues. 



M. de Saussure defines vegetable mould (humus) to be the black 

 substance which covers dead vegetables after they have been long 

 exposed to the combined action of water and oxygen, llis experi- 

 ments refer to mould nearly pure ; that is, separated by a fine sieve 

 from the vegetable remains which are always nnxed with it ; to 

 mould which had been gathered on high rocks, or from the trunks 

 of trees, where it could not have been exposed to admixture or to 

 any influence, other than that of the spontaneous decomposition by 

 which it had been produced. All the varieties of mould collected 

 in this way appeared terlile, especially when they were previously 

 mixed with gravel, which supplies support to the roots of plants, and 

 permits the access of the air. That variety, however, must be ex- 

 cepted which was obtained from the interior of trees, and had been 

 formed in such a situation tint the rain-w.iter which entered found 

 no free outlet ; the humus then contained extractive i)rinciples, de- 

 rived in part from the living {)lant, and which seemed to <»bstrucl the 

 pores of the vegetable io which it was applied as manure. 



In making comparative calcinations in close vessels of different 

 varieties of humus, and of plants similar to those from which they 

 had proceeded, and collecting the charcoal on one hand, and the 

 volatile and gaseous matters on the other, M. de Saussure di^covcr- 

 ed that they conlamed, for the same weight, a larger quantity of 

 carbon and of azote than the vegetables whence they proceeded. 

 The larger proj)orti(m of azote in the humus seeins to imply that 

 during tlieir dccom|)osition, vegetables do not throw otf this element ; 

 but to this cause must be added that w liich might be connected with 

 the spoils of insects which live in humus. 



