POTASSIUM, KUBIDIUM, CAESIUM, AND LITHIUM 545 



Common nitre occurs in nature, but only in small quantities in 

 admixture with other nitrates, and especially with sodium, magnesium, 

 and calcium nitrates. Such a mixture of salts of nitric acid is formed 

 in nature in fertile earth, and in those localities where, as in the soil, 

 nitrogenous organic remains are decomposed in the presence of alkalis 

 or alkaline bases with free access of air. This method of the formation 

 of nitrates requires moisture, besides the free access of air, and takes 

 place principally during warm weather. Besides which Schloessing and 

 Miintz, by employing similar methods to Pasteur, showed that the for- 

 mation of nitre in the decomposition of nitrogenous substances is 

 accomplished by the aid of peculiar micro-organisms (ferments) without 

 which the simultaneous action of the other necessary conditions 

 {alkalis, moisture, a somewhat elevated temperature, air, and nitroge- 

 nous substances) cannot give nitre. In warm countries, and in tempe- 

 rate climates during the summer months, fertile soils produce a small 

 quantity of nitre. In this respect India is especially known as affording 

 a considerable supply of nitre extracted from the soil. The soil, which 

 contains nitre, after the rainy season sometimes becomes covered 

 during the summer with crystals of nitre, formed by the evaporation 

 of the water in which it was previously dissolved. This soil is col- 

 lected, subjected to repeated lixiviations, and treated for nitre, as will 

 be presently described. In temperate climates nitrates are obtained 

 from the lime rubbish of demolished buildings which have stood for 

 many years, and especially from those portions which have touched 

 the ground. The conditions are there very propitious to the forma- 

 tion of nitre, because the lime used as a cement in buildings contains 

 the base necessary for the formation of nitrates, while the excrement, 

 urine, and other animal refuse are sources of nitrogen. By the metho- 

 dical lixiviation of this kind of rubbish a like solution of nitro- 

 genous salts is obtained as by the lixiviation of fertile soil. A similar 

 solution is also obtained by the lixiviation of the so-called nitre plan- 

 tations. They are composed of manure interlaid with brush-wood, and 

 strewn over with ashes and other alkaline and lime rubbish. These 

 nitre plantations are set up in those localities where the manure is not 

 required for the fertilisation of the soil, as, for example, in the south- 

 eastern * black earth ' governments of Russia. The same process of 

 oxidation of nitrogenous matter free to the access of air and mois- 

 ture during the warm season in the presence of alkalis takes place 

 in nitre plantations as is accomplished in the fertile soil and in the 

 walls of buildings. From all these sources there is obtained a solution 

 containing different salts of nitric acid mixed with soluble organic 

 anatter. The simplest method of treating this impure solution of nitre 



VOL. i. 



