DESCRIPTION OF A NITRE CAVE. 239 



to the bushel. Formerly the earth was taken out of the cave 

 and lixiviated near the stream, at present hoppers are erected 

 in the cave, and the earth after lixiviation, is left to be impreg- 

 nated again with nitrate of lime; but what length of time will 

 be requisite to saturate it, has not yet been ascertained. 



The workmen have different modes of forming an opinion 

 with regard to the quantity of nitre with which the earth may 

 be impregnated. They generally trust to their taste; but it is 

 always considered as a proof of the presence of nitre, when 

 the impression made on the dust by the hand or foot, is in a 

 very short time effaced. Where the nitre is very abundant the 

 impression made to-day, will be scarcely visible to-morrow. 

 Where there is a great deal of sand mixed with the dust, it is 

 commonly believed that a small quantity of pot-ash will suf- 

 fice for the saturation of the acid. 



The method of making saltpetre usually practised in Ken- 

 tucky, is as follows. 



The earth is dug and carried to hoppers of a very simple 

 construction, which contain about fifty bushels, cold water is 

 poured on it from time to time, and in a day or two a solution 

 of the salts runs into troughs placed beneath the hoppers. The 

 lixiviation is continued as long as any strength remains in the 

 earth. The liquor is then put into iron kettles, and heated to 

 ebullition; it is afterwards thrown upon a hopper containing 

 wood ashes, through which it is suffered to filtrate. As the 

 alkaline part of the ashes is discharged before the nitrate passes 

 through, the first runnings of this hopper are thrown back; 

 and alter some time, the clear solution of nitrate of pot-ash 

 runs out, mixed with a white curd, which settles at the bottom 

 of the trough. This clear liquor is boiled to the point of crys- 

 tallization, then settled for a short time and put into troughs to 

 crystallize, where it remains twenty-four hours, the crystals 

 are then taken out, and the mother-water thrown upon the ash- 

 hopper, with the next running of the nitrate of lime. When 

 the quantity of the nitrate of lime is too great for the portion 

 of ashes employed, the workmen say their saltpetre is in the 

 "grease" and that they do not obtain a due quantity of nitre. 

 If there has been too great a proportion of ashes employed, 



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