[ lOO ] 



refiduum ; and fecondly, as great a proportion of falt-pctre can- 

 not be extraded from damaged powder as is obtained from fervice- 

 able, though originally manufadured with the fame quantum of 

 nitre : Perhaps, in this Ruffian powder, the noxious quahties of 

 the magnefia and marine fait were fufficiently counteradled by the 

 native excellence of the nitre, aided by fome unknown fuperiority 

 in their method of combining and incorporating the materials. 



In the choice of falt-petre I fhould prefer that whofe cryftak 

 are of a moderate fize, foUd, tranfparently white, which do not 

 readily break with a crackling noife when gently grafped in the 

 hand, and which when ignited on a red hot fhovel do not decre- 

 pitate, but melt and confume with an equable and continued 

 inflammation : The firft of thofe fymptoms is produced by hafty 

 and imperfed dcficcation, and the laft is a proof that the marine 

 fait has not been entirely feparated from the nitre : I muft obferve 

 that however carefully the procefs of dcficcation is performed, the 

 cryftals will retain a certain portion of humidity (befides their 

 efl*ential waters) which when rarefied by the heat of the hand 

 produces a crackling noife ; this proof of the quality of nitre 

 rauft therefore depend on the degree of decrepitation. It may be 

 afl<ed, why take fuch pains to avoid moifture in nitre, when its 

 combination with the other materials of gun-powder is effeded 

 by water ? I anfwer, it is this particular fpecies of moifture I 

 objed to, known to falt-petre refiners by the name of mother- 

 waters, which taken up in the ad of cryftallization is replete 

 with a greafy magnefia and common fait. If the powder-maker 

 refines his nitre himfelf, I advife him to boil it thrice, carefully 

 (liimming off the fceculent matter which floats on the furface, 



and 



