and Detonating Matches. 125 



ought to remain on the salt for two or three hours ; and then it 

 may be suffered to drain off through the plug-holes below for 

 about an hour. 



All the liquor of drainage from the first watering, as well as 

 a portion of the second, is set aside, as being considerably 

 loaded with the foreign salts of the nitre, in order to be evapo- 

 rated in the sequel with the mother waters. The last portions 

 are preserved, because they contain almost nothing but nitre, 

 and may therefore serve to wash another dose of that salt. It 

 has been proved by experience, that the quantity of water em- 

 ployed in washing need never exceed thirty-six sprinklings in 

 the whole, consisting of three waterings, of which the first two 

 consist of fifteen, and the last of six pots ; or, in other words, of 

 fifteen sprinklings of water saturated with saltpetre, and 

 twenty- one of pure water. 



The saltpetre, after remaining five or six days in the wash- 

 ing chests, is transported into the drying reservoirs, heated 

 by the flue of the nearest boiler ; here it is stirred up from time 

 to time with wooden shovels, to prevent its adhering to the 

 bottom, or running into lumps, as well as to quicken the dry- 

 ing process. In the course of about four hours, it gets com- 

 pletely dry, in which state it no longer sticks to the shovel, 

 and falls down into a soft powder by pressure in the hand. 

 It is perfectly white and pulverulent. It is now passed 

 through a brass sieve, to separate any small lumps or foreign 

 particles accidentally present, and is then packed up in bags 

 or barrels. Even in the shortest winter days, the drying 

 basin may be twice charged, so as to dry 700 or 800 kilo- 

 grammes. By this operation, the nett produce of 3000 

 kilogrammes thus refined, amounts to from 1750 to 1800 kilo- 

 grammes of very pure nitre, quite ready for the manufacture 

 of gunpowder. 



The mother waters are next concentrated ; but into their 

 management it is needless to enter in this memoir. 



On reviewing the above process as practised at present, it 

 is obvious that, to meet the revolutionary crisis, its conductors 

 must have shortened it greatly, and have been content with a 

 brief period of drainage. 



