£48 - >>ITRIF1CATI0N. 



receives in tropical countries. It is there well known that toojnuch 

 stirring of the soil is i 'ten prejudicial even in irrigated lands, where 

 consequently the bad «.ffects cannot be attributed to too great a de- 

 gree of dryness. The information which has lately reached the 

 Academy of Sciences upon the agriculture of the French posses- 

 sions in Africa, tend to make us perceive that the same cause pro- 

 duces the same effects in Algeria, and that it is not without reason 

 that the Arabs only work their lands that are preparing for grain 

 crops, very superficially. 



Humus is, in fact, dissipated by a process of slow combustion in 

 the air : in contact with oxygen, it produces carbonic acid, as is 

 proved by the experiments of M. de Saussure. Pure humus, moist- 

 ened with distilled water, confined in bell-glasses placed over mci. 

 cury, formed carbonic acid, causing the disappearance of the oxygen 

 of the air. The. volume of the acid gas formed, corresponded i 

 volume with that of the oxygen wliieh had disappeared. Humus, 

 therefore, in contact with air, gives off carbonic acid, and the phe- 

 nomenon here still takes place as if carbon were not alone consumed. 

 The loss experienced is greater than that which ought to occur from 

 the quantity of carbon which unites with the oxygen ; and Saussure 

 concluded that there is, at the same lime, a lo^js of the elements of 

 water. The capital fact which results from these experiments of 

 Saussure, the deduction directly applicable to the theory of manures 

 is this : that humus is dissipated when it is exposed to the air, and 

 that during the slow combustion v.hich it undergoes, it is a constant 

 source of carbonic acid gas. 



To complete the views that may throw ligiit on the part played 

 by Hianures, I have still tp speak of an imj)orlant phenomenon which 

 occasionally takes place under the same ct>nditions as tliose that ac- 

 • company the decomposition, the putrefaction of animal matters: I 

 mean the sj)ontaneous formation of nitric acid — the occurrence of 

 nitrification as it is called. Nitric acid results iVom the union of 

 azote with oxygen. Such at lea.st is the constitution of this acid 

 when it is combined in s,ilts ; but in its isolated state, it is always 

 united with a certain ijuantity of water. It has not yet been obtain- 

 ed, and it appears indeed not to exist, in the perfectly dry or anhy- 

 drous state. The azote, therefore, does not couibine directly with 

 the oxygen ; tl\ere must be, at all events, the intervention of water, 

 and to effect the union of tlie two gases by means of the electric 

 spark, the mixture, according to Cavendish, nnist be moist. Never- 

 theless, the combination of azote with oxygen appears to be singular- 

 ly favored by the presence of earthy or alkaline bases, seeing thai 

 in nature the nitrates are met with in a certain abundance ; but the 

 circumstances which (Ictermine their tormation are still invi)lvetl ii? 

 deep obscurity. 



Three distinct origins may be assigned to the natnial nitrates: 

 1st. certain soils, still imliffcrently studied, show an etUorescence of 

 nitrate of potash on their surface, or by lixiviation yield large quan- 

 tities of this salt. Such is the source of the saltpetre which is iiu- 

 ported from India. 



