NITRIC ACID. 



but if the heat be urged too far, the ba- 

 rytes is apt to vitrify with the earth of the 

 crucible. It is soluble in 12 parts of cold, 

 and 3 or 4 of boiling 1 water. It is said to 

 exist in some mineral waters. 



The nitrate of potash is the salt well 

 known by the name of nitre, or salt- 

 petre. It is found ready formed in the 

 East Indies, in Spain, in the kingdom of 

 Naples, and elsewhere, in considerable 

 quantities ; but nitrate of lime is still 

 more abundant. 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 situa- 

 tions, where animal matters are com- 

 pletely decomposed with access of air, 

 and of proper substances with which it 

 can readily combine. Grounds frequent- 

 ly trodden by cattle, and impregnated 

 with their excrements, or the walls of in- 

 habited places where putrid animal va- 

 pours abound, such as slaughter-houses, 

 drains, or the like, afford nitre by long 

 exposure to the air. Artificial nitre beds 

 are made by an attention to the circum- 

 stances in which this salt is produced by 

 nature. Dry ditches are dug, and cover- 

 ed \vith sheds, open at the sides, to keep 

 off the rain : these are filled with animal 

 substances, such as dung, or other excre- 

 ments, with the remains of vegetables, 

 and old mortar, or other loose calcareous 

 earth ; this substance being found to be 

 the best and most convenient receptacle 

 for the acid to combine with. Occasional 

 watering, and turning up from time to 

 time, are necessary, to accelerate the 

 process, and increase the surfaces to 

 which the air may apply ; but too much 

 moisture is hurtful. When a certain por- 

 tion of nitrate is formed, the process ap- 

 pears to go on more quickly : but a cer- 

 tain quantity stops it altogether, and after 

 this cessation the materials will go on to 

 furnish more, if what is formed be ex- 

 tracted by lixiviation. After a succes- 

 sion of many months, more or less, ac- 

 cording to the management of the opera- 

 tion, 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 calcare- 

 ous earth. 



To extract the saltpetre from the mass 

 of earthy matter, 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, tog-ether with 

 wood-ashes, either strewed at top, or add- 

 ed 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 man- 

 ner, as long as any saline matter can be 

 thus extracted. The weak brine is heat- 

 ed, and passed through other tubs, until 

 it becomes of considerable strength. It 

 is then carried to the boiler, and contains 

 nitre and other sails; the chief of which 

 is common culinary salt, and sometimes 

 muriate of map;nesia. 



It is the property of nitre to be much 

 more soluble in hot than cold water; but 

 common salt is very nearly as soluble in 

 cold as in hot water. Whenever, there- 

 fore, 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 sepa- 

 rated is taken out, with a perforated la- 

 dle, and a small quantity of the fluid is 

 cooled, from time to time, that its con- 

 centration may be known by the nitre 

 which crystallizes in it. When the fluid is 

 sufficiently evaporated, it is taken out 

 and cooled, and great part of the nitre 

 separates in crystal ; while the remaining 

 common salt continues dissolved, be- 

 cause equally soluble in cold and in hot 

 water. Subsequent evaporation of the 

 residue will separate more nitre in the 

 same manner. 



This nitre, which is called nitre of the 

 first boiling, contains some common salt ; 

 from which it may be purified by solution 

 in a small quantity of water, and subse- 

 quent 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 con- 

 tained by the nitre, that very little of it 

 will crystallize. For nice purposes, the 

 solution and crystallization of nitre are re- 

 peated four times. The crystals of nitre 

 are usually of the form of six-sided flat- 

 tened prisms, with diedral summits. Its 

 taste is penetrating ; but the cold pro- 

 duced, by placing the salt to dissolve in 

 the mouth, is such as to predominate over 

 the real taste at first. Seven parts of 

 water dissolve two of nitre, at the tem- 

 perature of sixty degrees: but boiling 

 water dissolves its own weight. One 

 hundred parts of alcohol, at a heat of one 



