'156 POTASSIUM. 



at 464 (240o cent.), and of which the density is 2.296 (Jacque- 

 lin.) Its formula is 3HO, PO 5 + 2KO, SO 3 . It will be ob- 

 served that both these compounds agree with Mr. Phillips 's 

 sesquisulphate, in having two of sulphate of potash to one of 

 hydrated acid. 



Nitrate of potash, Nitre, Saltpetre; KO, NO 5 ; 1266.9 or 

 101.53. Nitric acid is formed in the decomposition of animal 

 matters containing nitrogen, when they are exposed to air, and 

 are in contact with alkaline substances. It appears to be 

 largely produced in this way in the soil of certain districts of 

 India, from which nitrate of potash is obtained by lixiviation. 

 Nitrous soils always contain much carbonate of lime, the debris 

 of tertiary calcareous rocks, in which the oxygen and nitrogen 

 of the air unite, according to some, assisted by the porous 

 structure of the rock, and under the influence of an alkaline 

 base, so as to generate nitric acid without the intervention of 

 animal matter. But this conjecture is not founded upon experi- 

 riment ; nor is it a necessary hypothesis, since nitrifiable rocks 

 are never entirely destitute of organic matter. Nitrate of po- 

 tash is also prepared in some countries of Europe, by imitating 

 the natural process, in artificial nitre-beds, wherein nitrate of 

 lime is formed, and afterwards converted into nitrate of potash 

 by the addition of wood- ashes to the lixivium*. 



Nitrate of potash generally crystallizes in long striated six- 

 sided prisms, is anhydrous, unalterable in the air, fusible into 

 a limpid liquid by a heat under redness, in which condition it is 

 cast in moulds, and forms sal prunelle. Its density is 1 .933 

 (Dr. Watson). According to Gay-Lussac 100 parts of water 

 dissolve 13.3 parts of this salt at 32, 29 parts at 64.4, 74.6 

 parts at 96.8, and 236 parts at 206.6o. The taste of the solu- 

 tion is cooling and peculiar ; it has considerable antiseptic pro- 

 perties. Nitre is insoluble in absolute alcohol. 



* The latest writer upon nitrification is Professor Kuhlman, whose observations 

 and original experiments are valuable, but do not lead to any general theory 

 of the process. He did not succeed in causing oxygen and nitrogen gases to 

 combine, by means of spongy platinum, but he found that, under the influence of 

 that substance, (1) all vaporisable compounds of nitrogen including ammonia, 

 mixed with air, with oxygen, or with an oxidating gas, change into nitric acid or 

 peroxide of nitrogen ; and (2) that all the vaporisabie compounds of nitrogen, in- 

 cluding nitric acid, mixed with hydrogen or a hydrogenous gas, give rise to am- 

 monia. (Memoirs of the Academy of Sciences of Lille, 1838, and Liebig's An- 

 nalen, Vol. 29, p. 272, 1839.) 



