1834.] On the method of extracting Saltpetre, 188 



-ally as roqurred, so that the boiling may not be checked by a large 

 addition of water at any time — this pan may be heated by a flue from 

 the furnace, by which means a considerable expenditure of fuel wiil 

 be saved. 



As a considerable quantity of earthy matter &c. will soon begin to 

 fall to the bottom of the boiler, and form a hand cake, which is ve- 

 ry injurious to the metal, a small pan ought to be placed in the 

 centre of the solution, raised two inches from the bottom of the boi- 

 ler, in which this earthy matter will collect, this pan is to be suspen- 

 ded by means of iron chains, connected by a rope to a pulley above, 

 so that it can be raised up from time to time, and its contents emp- 

 tied into a box or basket placed at the edge of the boiler, to allow 

 ' the water to drain back. It is essential that the solution should 

 boil at an equal steady temperature, increasing or diminishing the 

 fire as may be necessary, and the skum ought to be carefully and 

 frequently removed. 



When all the extra water has been added, the pan is to be with- 

 drawn from the bottom of the boiler — The common salt wiil then be- 

 gin to fall, and must be removed with a scoop ladle from the bot- 

 tom, and placed, in a basket as beforementioned to drain. 



It is proper at this period to decrease the fire which delays the 

 operation, but the results are thereby obtained with more regularity. 

 When the common salt falls to the bottom in abundance, the solu- 

 tion is approaching the proper degree of concentration, which may 

 be easily ascertained by taking out a small portion of the liquid and 

 placing it in a vessel to crystallize. &c. 



When it is judged proper to stop the operation the fire is to be 

 decreased, and the solution left t© repose, till the common salt 

 ceases to fall, or about five hours, during which time the solution 

 ought to be kept steadily at the temperature of about 88 Centigrade 

 thermometer or 190 of Farenhiet when it may be drawn off from 

 the surface into crystallizing pans, taking every care to leave uiOf 

 disturbed, the salt or sediment at the bottom. It will require three 

 days to complete the crystallization in winter, and longer in sum- 

 mer, and during hot weather fewer crystals will be obtained. 



The mother water is then to be removed from the pans, and they 

 are to be put up to drain, two and two, inclining towards each other 

 in a channel. 



In the manufactories of the Administration the crystallization is 

 determined, by a much more easy and expeditious operation, the 

 wat^r is run off, into a long and large reservoir, lined with sheet 

 lead or copper^ the interior dimension* of which is about 12 feet 



