668 



POTASH 



'litre. Three parts of nitre, two of sub-carbonate 

 of potash, and one of sulphur, mixed together, form 

 the pulvis fulminans, a small quantity of which, 

 laid on a fire shovel, and held over the fire till it 

 lieu ins to melt, explodes, with a loud, sharp noise. 

 Mixed with sulphur and charcoal, it forms gun- 

 powder, (q. v.) Three parts of nitre, one of sul- 

 phur, and one of fine saw-dust, well mixed, consti- 

 tute the powder of fusion. If a bit of base copper be 

 folded up, and covered with this powder, in a 

 walnut shell, and the powder be set on fire with a 

 taper, it will detonate rapidly, and fuse the metal 

 into a globule of sulphuret, without burning the 

 shell. The sources of nitre are as follows : It is 

 found ready formed in the East Indies, in Spain, in 

 the kingdom of Naples ; and it abounds in the 

 limestone caves of the western and south-western 

 states of America, in which last-mentioned situa- 

 tions it is rarely found ready formed, but is obtained 

 from the nitrate of lime, which is changed to nitre 

 by being mingled with wood-ashes, and leached. 

 Far the greater part of the nitrate made use of is 

 produced by a combination of circumstances, which 

 tend to compose and condense nitric acid. This 

 acid appears to be produced in all situations where 

 animal matters are completely decomposed with 

 access of air, and of proper substances with which 

 it can readily combine. Ground frequently trodden 

 by cattle, and impregnated with their excrement, 

 or the walls of inhabited places, where putrid 

 animal vapours abound, such as slaughter-houses, 

 drains, or the like, afford nitre by long exposure to 

 the air. Artificial nitre beds are made by an atten- 

 tion to the circumstances in which the salt is pro- 

 duced by nature. Dry ditches are dug, and covered 

 with sheds, open at the sides, to keep off the rain ; 

 these are filled with animal substances of all kinds, 

 and occasionally watered, and turned up, from time 

 to time, to accelerate the process by increasing the 

 surfaces to which the air may apply. When a cer- 

 tain portion of nitrate is formed, the process appears 

 to go on more quickly ; but a certain quantity stops 

 it altogether, and, after this cessation, the materials 

 will go on to furnish more, if what is formed be 

 extracted by lixiviation. After a succession of 

 many months, more or less, according to the 

 management of the operation, in which the action 

 of a regular current of fresh air is of the greatest 

 importance, nitre is found in the mass. If the beds 

 contained much vegetable matter, a considerable 

 portion of the nitrous salt will be common saltpetre ; 

 but if otherwise, the acid will, for the most part, 

 be combined with the calcareous earth ; to extract 

 the saltpetre from which, a number of large casks 

 are prepared, with a cock at the bottom of each, 

 and a quantity of straw within to prevent its being 

 stopped up : into these the matter is put, together 

 with wood-ashes, either strewed at top or added 

 during the filling. Boiling water is then poured 

 on, and suffered to stand for some time, after which 

 it is drawn off, and other water added, in the same 

 manner, as long as any saline matter is afforded. 

 The weak brine is heated, and passed through other 

 tubs, until it becomes of considerable strength ; it 

 is then carried to the boiler. It contains nitre and 

 ther salts, the principal one of which is common 

 salt. It is the property of nitre to be much more 

 soluble in hot than in cold water, as has been seen 

 above ; but common salt is very nearly as soluble 

 in cold as in hot water. Whenever, therefore, the 

 evaporation is carried by boiling to a certain point, 

 much of the common salt will fall to the bottom, 

 for want of water to hold it in solution, though the 

 nitre will remain suspended by virtue of the heat. 

 The common salt thus separated is taken out with 



a perforated ladle ; and a small quantity of the fluid 

 is cooled, from time to time, that its concentration 

 may be known by the nitre which crystalizes in it. 

 When the fluid is suiliciently evaporated, it is taken 

 out and cooled, and a great part of the nitre sepa- 

 rates in crystals, while the remaining common salt 

 continues dissolved, because equally soluble in cold 

 as in hot water. Subsequent evaporation of the 

 residue will separate more nitre in the same manner. 

 By the suggestion of Lavoisier, a much simpler 

 plan was adopted ; reducing the crude nitre to 

 powder, and washing it twice with water. This 

 nitre, which is called nitre of the first boiling, con- 

 tains some common salt, from which it may be 

 purified by solution in a small quantity of water, 

 and subsequent evaporation ; for the crystals thus 

 obtained are much less contaminated with common 

 salt than before, because the proportion of water 

 is so much larger, with respect to the small quantity 

 contained by the nitre, that very little of it will 

 crystalize. The uses of nitre are various. Besides 

 being employed in the composition of fluxes, and 

 for the purposes of metallurgy, it serves to promote 

 the combustion of sulphur in fabricating sulphuric 

 acid. It is used in the art of dying ; it is added to 

 common salt for preserving meat, to which it gives 

 a red hue ; it is prescribed in medicine as a cooling 

 febrifuge and diuretic ; and some have recommended 

 it, mixed with vinegar, as a very powerful remedy 

 for the sea-scurvy. 



Sulphate of potash is formed by adding diluted 

 sulphuric acid to a solution of carbonate of potash, 

 until the acid and alkaline properties are neutralized. 

 It crystalizes in six-sided prisms, with pyramidal ter- 

 minations, and requires for its solution seventeen 

 parts of water at 60, and five parts at 212. Its 

 taste is bitter. 



Bi-Sulphate of potash is the salt remaining after 

 the decomposition of nitre by sulphuric acid. It 

 contains twice the quantity of acid in the sulphate, 

 has a very sour taste, and reddens vegetable 

 colours, and is more soluble than the sulphate. 



Phosphate of potash forms a gelatinous mass, 

 which attracts humidity from the atmosphere ; its 

 taste is saline, with a degree of sweetishriess. 



Sub-orate of potash is soluble in water, and by 

 evaporation affords prismatic crystals, which are 

 not changed by exposure to the air. 



Muriate of potash has a saline taste, which is 

 slightly bitter. Its crystals are cubic, and decre- 

 pitate when heated. 



Chlorate of potash, or hyperoxymuriate, may be 

 formed by receiving chlorine as it is formed into a 

 solution of potash. When the solution is saturated, 

 it may be evaporated gently, and the first crystals 

 produced will be the salt in question. They are 

 shining, hexahedral lamina?, or rhomboidal plates. 

 Its taste is cooling and disagreeable. Specific 

 gravity, 2. Sixteen parts of water at 60, and 

 two and a half of boiling water, dissolve one of it. 

 The purest oxygen is obtained from this salt, by 

 exposing it to a gentle heat. Its effects upon 

 inflammable substances are very powerful. Two 

 grains, rubbed into a powder in a mortar, and 

 mingled with one grain of sulphur, give a loud 

 detonation when struck upon an anvil with a 

 hammer. Five grains of the salt, mixed, in the 

 same manner, with two and a half of charcoal, will 

 be inflamed by strong trituration. If a little sugar 

 be mixed with half its weight of the powdered 

 chlorate, and a little strong sulphuric acid poured 

 on it, a sudden inflammation will ensue. If to one 

 grain of the salt in a mortar we add half a grain of 

 phosphorus, and communicate to itaslight trituration, 

 it will detonate with great violence, and attended 



