246 HUMTTS. 



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

 deop brown color, and contains as prinjipal 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 sahs, and by the way of double decomposition, 

 insoluble ulmates. M. Peligot assigns to ulmine the following 

 composition : 



Carbon 72.3 



Hydrogen 6-2 



Oxygen .-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 present day can add but little 

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

 cherches Chimiques. 



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. His experi- 

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

 from the vegetable remains which are always mixed 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 fertile, 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 that the rain-water which entered found 

 no free outlet ; the huriius then contained extractive principles, de- 

 rived in part from the living plant, and which seemed to obstruct the 

 pores of the vegetable to 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 discover- 

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

 carbon and of azote than the vegetables whence they proceeded. 

 The larger proportion of azote in the humus seems to imply that 

 during their decomposition, vegetables do not throw off this element* 

 but to this cause must be added that which might be connected with 

 the spoils of insects which live in humus. 



