NITEOGEXOUS MANURES. 219 



bases (carbonate of lime)/ However, this spontaneous formation 

 in the soil is very slow in our climate. It is, on the other hand, 

 very rapid in Southern countries, Bengal, Hungary, Spain, where 

 the^ conditions of temperature and of moisture in the air conduce 

 considerably to the oxidation of nitrogenous animal matter. 



For a long time these countries where nitrates exude spontane- 

 ously from the soil, and cover it wdth a layer like hoar frost, alone 

 supxDlied Northern Europe, up to the time when they succeeded 

 in making mixtures of soil to produce saltpetre. This industry was 

 conducted in saltpetre fields. Limestone, marl, washed wood ashe& 

 were mixed with animal matter, urine, dung, straw, etc. Heaps were 

 made, whicli were left to themselves in the open air for nearly a. 

 year, frequently turning them. When the earth was ready, that. 

 IS to say enriched, it was Uxiviated. To eliminate the hme from 

 the liquor obtained, it was treated with wood ashes, and clarified,, 

 and evaporated to obtain saltpetre. That method, which requires, 

 much work and only gives poor results, could only be applied in 

 countries which, deprived from communication with the south, as in 

 time of war, were obliged to live on their own resources, as France" 

 and Germany were during the continental hlociis. This method, 

 therefore, was abandoned. 



But the sources of saltpetre indicated above barely met the 

 wants of industry ; agriculture could not profit. The discovery 

 of an important deposit of nitrate of soda in Ameiica, the working 

 of which was commenced in the years 1825-28, enabled the wants 

 of agriculture to be met. 



Chili Nitrate of SWa.— South American nitrate of soda is dis- 

 tinguished, more especially from ordinary saltpetre, by the fact 

 that its acid is combined with another alkali. In Indian saltpetre 

 It is combined with potash (KNO3), whilst in Chili saltpetre it is com- 

 bined with soda (NaN03). It is met with in the Pampas of Peru, 

 of Chili, and Bolivia, between 19° and 27° of south latitude; it 

 abounds especially in the province of Tarapaca (formerly Peruvian, 

 now Chilian) and in the desert of Atacama. The nitrous mineral 

 caliche, or terra salitro^a, occurs as a layer of 1 to 6 inches thick 

 under a bed of conglomerate, consisting of sand, feldspar and 

 pebbles, amalgamated by a cement consisting of clay and different 

 salts forming a bed 20 to 30 inches thick. Its colour varies from 

 grey to brown. The conglomerate bed is sometimes awanting, so- 

 that the mineral crops out at the surface. 



The caliche is never pure nitrate of soda. It contains mixtures 

 of nitrate of potash, common salt, iodide and bromide of sodium,, 

 alkaline sulphates, sulphate of lime mixed with sand. It only 

 contains on an average 25 per cent of nitrate. Picked pieces 

 contain more. The following gives the percentage in nitrate of 

 different products : — 



