REPORT ON NITRIFICATION. 311 



general impression than from positive knowledge. It is not to be 

 forgotten that this is a crop which, when once reaped, it will take 

 years to renew. 



Probably the best mode of managing these caves, in view of a 

 national emergency, would be to carry into them quantities of a nitri- 

 fiable earth, preferably one arising from the decomposition of a felds- 

 pathic rock, and to leave it there until a serious call for nitre should 

 arise. 



The earth of caverns is nowhere worked as a source of nitre to 

 a very important extent; but a formation of nitrates, which goes on 

 under circumstances somewhat similar to those prevailing in caves, 

 is in Europe one of the chief indigenous modes of production. In old 

 buildings, especially in cellars and in damp outhouses, nitrate of lime 

 is found largely in the mortar, the plaster, and sometimes in a porous 

 limestone which has been used as a building material. We have 

 here, as in caves, a protection from rain, and a moist atmosphere; 

 there is also, however, in many cases a particular exposure to the 

 emanations from decaying organic matters, as in the cellars and 

 foundations of buildings in a badly-drained soil. The decay of walls 

 from the formation of nitrates is known as the saltpetre rot, (saltpe- 

 tre frass.) The French, during the wars of the revolution, were greatly 

 indebted to this source for their supply of saltpetre. 



A rather unique nitre formation is that of South America, where 

 nitrate of soda, a salt not occurring largely elsewhere, is found in 

 immense quantities. In the desert of Atacama, which lies on the 

 western slope of the Andes, at the boundary between Peru and Chile, 

 it forms beds of from two to three feet in thickness, in which it is 

 mixed with various impurities.* It is also diffused through the soil 

 over a large extent of ground. Other parts of the desert are covered 

 with an efflorescence of saline matters, chiefly of sulphate of soda.f 



The nitrate of soda has been long known in commerce under the 

 names of cubic nitre and of Chile saltpetre, and being cheaper than 

 nitrate of potash, has been largely used for the manufacture of nitric 

 acid, and for other purposes where a nitrate is required.:}: It is too 

 deliquescent to be readily used as an ingredient of gunpowder, but, 

 like the other nitrates, it can be converted into saltpetre by the action 

 of a salt of potash. 



If it were desired to get a large quantity of a nitrate at once, the 

 nitrate of soda would be the most available, being ready formed and 

 accumulated to an immense extent. It is not certainly known whether 

 the production in these South American beds is continuously going 

 on, or whether the nitrate has resulted from actions which have now 

 ceased. Speculations as to the origin of this formation would require 

 a detail of circumstances which it is not, perhaps, worth while entering 

 upon. 



"~ Silliman's Journal, vol. 39, p. 375. 



f Chemical Society's Quarterly Journal, 1855, p. 308 ; also Chemist, 1855, p. 345. 



i Nitrate of soda was first carried to Europe ia 1820 In 1831 it came into use, and 

 since then has been an important article of commerce. The quantity imported into Great 

 Britain in 1850 was about 12,000 tons. The price in 1851 was 15s. per cwt. — Ure's Diet. 



