312 REPORT ON NITRIFICATION. 



There arc two cases of the production of nitrates in nature which 

 seem rather to belong to a ckiss by themselves, or at least to have 

 strong points of dissimilarity from any other well known instances. I 

 allude to the nitre-bearing chalk of the basin of Paris and the nitrif- 

 erous caves of Ceylon. In both localities the face of the rock, when 

 chipped off, is found to be impregnated with nitrates, which renew 

 themselves on the exposed surface twice a year or oftener, and some- 

 times appear as an efflorescence. In the French formation the pro- 

 duct is nitrate of lime, which forms where the rock is exposed to the 

 southward, and chiefly in hot and damp weather. The quarries have 

 been long worked, and the annual product is said to be about 15,000 

 pounds. 



The nitre caves of Ceylon, Avhich are between twenty and thirty 

 in number, are excavations in a porous rock, consisting of limestone, 

 talc, and feldspar. The nitrates formed are those of potash, lime, 

 and magnesia, the former predominating. Several of the caves were 

 visited and examined by Mr. John Davy. One of them he describes 

 particularly as a cavity of regular shape, about 200 feet long and 100 

 broad. In it sixteen workmen are employed during six months of 

 the year in chipping off the face of the rock and in extracting the 

 nitre from the stone thus collected. Each of the men pay as an 

 annual tithe to the government a half cwt. of nitre, so that the total 

 quantity obtained must be considerable. 



In these caves, as well as in the French quarries, it is only to the 

 depth of a fraction of an inch below the surface of the rock that the 

 nitrates are found, and after this thin coat has been removed it re- 

 quires from one to six months for the fresh surface to become im- 

 pregnated. In both these instances the conditions under which 

 nitrification goes on are very similar, taking place on the surface of a 

 porous rock which is continually moist, and is exposed to a warm 

 temperature, for in France the nitrates form only on a southern ex- 

 posure, and mainly during summer. The action is a more rapid one 

 than that of the ordinary nitrification of the earth in caverns, and is 

 to be distinguished from it. The formation of nitrates on the surface 

 of a rock is said to take place to a less extent in other localities, among 

 them in some caves in this country, but the nitrification in our west- 

 ern caves appears to be, mainly at least, that of the earth on their 

 floors. 



Both the Paris chalk and the Ceylonese caves have been cited as 

 good arguments for nitrification without access of organic matters. 

 We may, perhaps, imagine the filtration of water charged with the 

 products of organic decomposition into the rock, and it has been sup- 

 posed by some that the nitrogen of the animal remains which are 

 contained in limestone may become a source of nitrates. There is 

 one point, however, to be noted in regard to the nitriaries of the 

 Seine: that the chips of stone, after being lixiviated, are heaped up 

 into Avails, on the surface of which the nitrate forms as on the rock 

 itself. This seems to point to the texture of the rock as the cause 

 of nitrification rather than any supply of oi'ganic matter. 



