POTASH, NITRATE OF 595 



Preparation. 1. By lixiviation of earth impregnated with the salt. The earth is 

 heated with water in tanks or tubs with false bottoms, and after sufficient digestion 

 the solution is run off and evaporated to crystallisation. The nitre procured by the 

 first operation is exceedingly impure, and contains large quantities of chloride of 

 potassium, and some sulphate of potash. By repeated crystallisations the salt may 

 be obtained pure. If the crude product of the lixiviation contains, as is often the 

 case, the nitrates of lime or magnesia, they may bo got rid of by the addition of car- 

 bonate of potash ; the earths are precipitated as carbonates, and may be filtered off, 

 while an equivalent quantity of nitrate of potash is formed, and remains in solution, 

 thus : 



CaO.NO 5 + KO.CO" = CaO.CO 2 + KO.NO 5 . [Ca(WO 3 ) + X 2 CO 3 = CaCO 3 + 2KKTO 3 .] 



2. The second mode of preparing nitre which we shall consider, is from nitrate of 

 soda and chloride of potassium. On dissolving equivalent quantities of these two 

 salts in water, and sailing down, double decomposition takes place. The chloride of 

 sodium may bo removed from the hot concentrated fluid by means of shovels, while 

 the nitrate of potash, being much more soluble in hot than in cold water, remains in 

 solution, but crystallises out on cooling. The decomposition takes place in accordance 

 with the annexed equation : 



NaO.NO 5 + KC1 = Nad + KO.NO 5 . (NaSTO 3 + XC1 = NaCI ~ KKTO 3 .) 



The above reaction is one of great interest and importance, inasmuch as it enables 

 us to convert Peruvian or ' cubic nitre,' as nitrate of soda is sometimes called, into the 

 much more valuable salt, nitrate of potash. During the last war with Russia it was- 

 found that large quantities of chloride of potassium were exported, and found their 

 way into that country. For some time no notice was token, because the salt appeared 

 too harmless to be declared contraband of war. Eventually it was found that it was 

 entirely used in Russia for the purpose of affording nitrate of potash, by the process 

 described. It need scarcely be said that the gunpowder made through the medium of 

 our own chloride of potassium was employed against our troops in the Crimea. 



3. Nitre may of course be prepared by neutralising nitric acid by means of carbo- 

 nate of potash, or the caustic alkali. The process is evidently too expensive to be 

 employed, except for the purpose of experimental illustration, or under other special 

 circumstances. 



The formation of nitre in the earth of hot climates is probably in most cases due 

 to the decomposition of nitrogenised organic matters. The subject of nitrification is 

 one upon which some controversy has taken place. It is supposed by some chemists 

 that the chief source of the nitric acid is the ammonia produced during the decay of 

 nitrogenous matters. The presence of bases appears to have a remarkable ten- 

 dency to increase the production of the acid. It has been asserted that the ammonia 

 which is produced suffers partial oxidation, the acid formed uniting with the undecom- 

 posed ammonia to form the nitrate of that alkali. On the other hand, it has been 

 argued that the ammonia does not suffer oxidation, but that the nitrogen prodxiced during 

 the decay of organic matter combines, at the instant of its liberation with oxygen, to 

 form nitric acid, which unites with the bases present. Nitrate of ammonia, no matter 

 how formed, suffers double decomposition in presence of the carbonates of the alka- 

 line earths, the result being the production of the nitrates of lime and magnesia. It is 

 owing to the presence of the two latter salts in the crude liquor obtained by lixiviating 

 nitrified earth, that the addition of carbonate of potash is so important, and causes so 

 great an increase in the produce of nitre. It has been insisted by some observers 

 that the presence of nitrogenous organic matters is not essential to the production of 

 nitre. In support of this, it has been shown that large quantities of nitrates are often 

 found where little or no organic matters are present. This has been explained by 

 assuming that porous bodies have the power of absorbing water, oxygen, and nitrogen, 

 and producing nitric acid from them. But it is evident that other forces exist cap- 

 able of inducing the oxidation of atmospheric nitrogen. It has been experimentally 

 demonstrated that nitric acid is produced during the discharge of atmospheric electri- 

 city. It is also probable that ozone plays an important part in the phenomena of 

 nitrification. Perhaps most of the chemists who have investigated the subject, have 

 been too anxious to assign the formation of nitre to one particular cause, whereas, the 

 phenomena which have been noticed by different observers are in favour of the idea 

 that several agencies are at work during the production of nitrates in the earth and in 

 artificial nitre-beds. 



During the time that France was fighting single-handed against the rest of Europe, 

 great difficulty was found in obtaining sufficient nitre for the production of the vast 

 amount of gunpowder necessary to enable her artillery to bo effectively supplied with 

 ammunition. This led the French chemists to establish artificial nitre-beds in various 



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