1 78 Mr. Graham's Account of M. Longchamp's TheoTy 



that the nitrate of potash resulted from the decomposition of 

 the nitrate of lime by some salt of potash. 



But it cannot be denied, that the nitrification of calcareous 

 substances is greatly promoted bj' the contact, oi', more ge- 

 nerall}', by the proximity of putrescent vegetable and animal 

 matter. The experiment of Thouvenel, to which M. Long- 

 champ refers above, abundantly proves this ; and the constant 

 and universal practice in the formation of artificial nitre-beds 

 strongly confirms it. This fact appears, therefore, to weigh 

 heavily against the theory of M. Longchamp : it is, however, 

 in our opinion, susceptible of an explanation without any mu- 

 tilation of that theory ; and to this extension of the hypothesis 

 we now proceed. 



We are disposed to attribute the beneficial effect in nitri- 

 fication of the decomposition of animal and vegetable matter, 

 to the plentiful supply of an element which exists at all times 

 in the atmosphei'e in a perceptible proportion — carbonic acid 

 gas. The free carbonic acid renders a portion of the carbonate 

 of lime soluble in the laater or moisture, 'which must be present ; 

 and thereby enables the carbonate of lime to act more effectually 

 upon the oxygen and azote, 'which the 'water has absorbed. The 

 oxygen, azote and carbonate of lime are all liquefied, and in 

 solution in the water; they are therefore in circumstances 

 most favourable to their mutual action. 



Carbonate of lime is altogether insoluble in pure water, 

 while water saturated with carbonic acid dissolves 1 -1500th 

 part. According to Dr. Thomson*: "when carbonate of lime 

 is rendered soluble in water by means of carbonic acid, a bi- 

 carbonate is formed, which seems only capable of existing in 

 solution." That carbonic acid is one of the most considerable 

 products of the putrefaction of both animal and vegetable sub- 

 stances, is well known. 



Water in ordinary circumstances absorbs rather more than 

 an equal volume of carbonic acid gas. 



Now Thouvenel, without any view to this point, performed 

 and has registered a series of experiments, which render it 

 exceedingly probable, that of the products of putrefaction, it 

 is the carbonic acid alone which contributes to the nitrifica- 

 tion ; inasmuch as when these products were deprived of their 

 carbonic acid, by being passed through caustic potash or lime- 

 water, before acting upon the chalk, their nitrifying power 

 was lost; while otherwise their nitrifying power was sufficiently 

 notable. I shall give Thouvenel's experiments as reported 

 hy Messrs. Aikin in their Chemical Dictionary, which is 



• First Principles, ii. 296. 



still 



