596 POTASH, NITRATE OP 



parts of the country. The success of the process may be judged of from the fact that 

 they yielded 2,000 tons annually. 



Nitre crystallises in colourless six-sided prisms. The crystals are anhydrous ; large 

 specimens when broken, however, generally show the presence of a little moisture 

 mechanically adhering to the interstices. If wanted in fine powder, it must therefore 

 be first coarsely bruised, and then dried, after which it may bo finely pulverised and 

 sifted. 



By the careful application of heat, nitrate of potash may be melted without under- 

 going any decomposition or loss of weight. But if the heat be raised to redness, it 

 begins to decompose, the degree to which the change takes place depending on the 

 amount of heat and the time of exposure. By carefully heating, for some time, a 

 large quantity of nitrite of potash is formed, oxygen gas being evolved. If the heat 

 be raised, or the exposure to a high temperature be continued, a large quantity of 

 nitrogen accompanies the oxygen, and the nitre becomes more and more changed, 

 until finally, a mixture of potash with peroxide of potassium is attained. If copper 

 filings, clipping, or shreds be mixed with the nitre, the decomposition proceeds much 

 more readily, and Wohler has proposed to prepare pure potash by this means. At 

 high temperatures nitre is a potent agent of oxidation, so much so, that the diamond 

 itself is attacked and converted into carbonic acid, which unites with the potash. 

 Crystallised boron, which is said to equal if not exceed the diamond in hardness, is 

 not attacked by fused nitre. The oxidising power of nitre is made use of in the arts 

 in order to obtain bichromate of potash from chrome iron ore. 



Nitrate of potash is sometimes used as a source of nitric acid, but nitrate of soda is 

 in every way more economical. This will be evident when it is considered that it 

 takes 101 parts of nitrate of potash to yield one equivalent of dry nitric acid (54 parts), 

 whereas 85 parts of nitrate of soda yield the same amount of acid. See NITRIC ACID. 



Nitrate of potash is employed in blow-pipe experiments, in order to assist in the 

 production of the green reaction characteristic of the presence of manganese. It 

 often happens where the quantity of manganese is exceedingly small, as in rose 

 quartz, that the green coloration with soda on platinum foil cannot be obtained ; if, 

 however, a little nitre be added, and the testing be repeated, the reaction generally 

 appears without any trouble. 



Nitrate of potash is greatly employed in the preparation of pyrotechnic mixtures. 

 It ought always to be well dried and reduced to fine powder before being used. 



Nitre is not unfrequently employed by the chemist for determining the percentage 

 of sulphur in coal. For this purpose the coal, reduced to fine powder, is mixed with 

 nitre and carbonate of soda, and projected by small portions into a silver crucible, 

 maintained at a red heat. A platinum crucible must not be employed, as it is attacked 

 by nitre in a state of fusion. The sulphur in the coal is converted, by the oxidising 

 agency of the nitre, into sulphuric acid ; the latter can then be converted into sulphate 

 of baryta, and the percentage of sulphur ascertained from its weight. 



Estimation of the Value of Nitre. A great number of processes have been devised 

 for the determination of the percentage of pure nitrate of potash in samples of the 

 crude salt. All these processes are more or less incorrect, and a really accurate mode 

 of determining the value of nitre has long been felt as a want by chemists. This 

 want has been supplied by Messrs. Abel and Bloxam of the Woolwich Arsenal, who 

 have devoted much labour and skill to the subject. Before detailing the successful 

 process of the latter chemists, wo will take a brief glance at the other methods com- 

 monly used for the purpose. The French process depends upon the principle that 

 a solution, when saturated with one salt, is still capable of dissolving a considerable 

 quantity of saline matter differing in its nature from the first. If, therefore, a satu- 

 rated solution of nitre be poured upon pure nitre, -no more is dissolved if the tempera- 

 ture remains the same as it was when the original solution was prepared. But if, on 

 the other hand, the saturated solution of nitre be digested with an impure sample con- 

 taining the chlorides of sodium, potassium, &e., the latter salts will be dissolved, and 

 the pure nitre remaining can, after proper draining, &c., be dried and weighed. The 

 loss of weight obviously represents the impurities removed. This process is subject 

 to so many sources of error that the practical details need not be entered into. 



Another mode of valuing nitre consists in fusing the salt, and, after cooling, break- 

 ing the cake : the fineness or coarseness and general characters of the fracture are the 

 means whereby the greater or less value of the salt are ascertained. This process, 

 which is known as the Swedish or Swartz's method, is far too dependent on the indi- 

 vidual experience and dexterity of the operator to bo of any value in the hands of the 

 chemist whose attention is only now and then directed to the valuation of saltpetre. 

 Moreover, although those who are in the habit of using it possess some confidence in 

 its correctness, it is quite evident that it is impossible for such an operation to yield 

 results of analytical accuracy. 



