26 Spfeity Procefsfor refining Saltpetre. 



' 'ft is fcarccly necefTary to obferve that the tubs muft ftand fufRciently apart, and be fo 

 difpofed that the work may be eafy and convenient. 



A boiler of a conical form, five feet wide and four deep, will ferve for three operatiorts 

 ■per day, and confequently to refine fifteen thoufand weight. A Cngle man is fufHcient to 

 attend the boiler. 



The veflel for cryftallization is of lead or copper, and muft be as near the boiler as poflible. 

 Its depth is fifteen inches, its length ten feet, and its width eight. It muft be placed on 

 a very folid fupport, fo that its bottom may every where reft upon it. It is convenient to 

 raife this fupport of mafonry about twelve inches above- the ground. By this means the 

 borders of the cryftallizing veflel will be 27 inches above the floor, which will render the 

 operation eafy and convenient. 



It has appeared to us of advantage to give to the bottom of the cryftallizing yeflel, an 

 inclination of four inches from the fides to the middle, merely in the longitudinal direc- 

 tion. The folutions may be emptied for feveral fuccefiive times from the boilers into the 

 cryftallizing veflTel, after having taken out the cryftals depofited from each folutibn. 



Four men appear neccflary for the operation of the cryftallizing veflel. Their bufinefs 

 is to agitate the fluid continually with the rakes. They colledl without intermiflion on 

 the borders of the veffel the cryftals which fall down, and convey them with a Ikimiricr to 

 the bafliets prepared for their reception and draining. Thefe fame workmen put the falt- 

 petre into the wooden veflTel for the laft wafliing and drainage, and carry the refined falt- 

 petre into the magazine. < 



For want of a large cooler for cryftallization a fhallow boiler may be ufed, or the faQie 

 veflels which ferve for cryftallization in the prefent works for refining this fait. 



To prepare the faltpetre for the manufaclure of gunpowder, it may be dried, after re» 

 fining, by two procefl"es, (i) by expofing it to the open air, or the fun, for feveral hours, 

 upon tatles ; or (2) by expofing it in a fhallow metallic veflel for two hours, to the heat of 

 40 or 50 degrees (about 135 Fahrenheit). In either cafe it muft be agitated and ftirred, 

 witli'fcarcely any interruption, in order to dry it fpeedily and equally. 



Confiderable experience has fhewn us, that the procefs here defcrlbed is the moft fimple 

 and economical. But, to prevent others from trying fuch methods as might feem ptomifing, 

 though we have thought fit to rejeft them, it will be proper to ofix:r the following remarks : 



1. Trial has been made to diflTolve the faltpetre, cryftallize it, and then wafti it to fcpa- 

 rate,the fea-falt. 



This procefs appears moft advantageous at firft fight, becaufe it faves the pounding ; but 

 It has great inconveniences, i. Crude faltpetre diflblved in 50 per cent, of water, and 

 poured into the veflel for cryftallization, does not depofit the fame quantity of faltpetre 

 as it would do if ivafhed before the folution. This difference depend? on the muriate of 

 foda in the crude faltpetre, which facilitates the folution of the nitrate of potafli, and con- 

 fequently the water of the cryftallizing veflels muft retain in folution more nitrate of pot- 

 afli, when the crude faltpetre is diflblved, than when it has been previoufly waflied with 



cold 



