to Jit It for domejlic Purpofes. 41 



regard to cleanlinefs and health, to purify it from this hete- 

 rogeneous fuhftanee which covers all the faces of its cryftals. 



Hitherto this fait has been purified or refined only by fo- 

 lution, filtration, or precipitation, according as the opera- 

 tion is performed on a large or a fmall fcale, and then by 

 evaporation. This method requires time, wood or charcoal, 

 and proper veflels. Many perfons, however, are unacquainted 

 with this procefs ; fometimes they have not leifure to employ 

 it ; and loinctimes they have neither the neceffarv vefTels nor 

 fuel. 



I have thought, therefore, that a procefs which requires 

 neither fire nor particular veflels, is attended with noexpenfe, 

 may be practifed at all times, and is within the reach of every 

 one, might be of general utility. This method is as follows: 



Take four ounces of gray fait, and, if dry, befprinkle it 

 gently with water till it be only what is called moid:; but it 

 will be very feldom necefTary to have recourfe to this opera- 

 tion. Put the fait into the corner of a table napkin or piece 

 of linen cloth, and form the cloth into a kind of knot or bag, 

 which you mint hold in one hand, while with the other you 

 rub and fhake the fait againft the infide of the cloth for the 

 fpace of half an hour. Then fhift the fait to another place 

 of the cloth, fucceflively repeating the fame manoeuvre fix, 

 feven, or eight times, according as the fait is more or lefs 

 gray. After the fait has been rolled for the firft time, the 

 cloih begins to exhibit foots occasioned by the earth which 

 the fait depofits, and of which the intenfitv fenfibly decreafes 

 at each change of place till they entirely difappear. In ge- 

 neral, the fait muft be befprinkled every two or three times 

 that its place is changed. The bleaching will be accelerated 

 by pounding the fa 1 1 flightly before it is befprinkled. 



After two or three afperfions and rubbings, the fait is, in 

 general, as pure and white as that refined, according to the 

 ufual method, by folution and evaporation. The lofs in both, 

 cafes is nearly the fame ; that is to fay, about an eighth, 

 when the fait is drv, and when care has been taken at each 

 change of place to fhake off the grains which adhere to the 

 cloth. It is, for the molt part, the whiteft fait that adheres 

 in this manner; and it may be fhaken off without fear, as 

 the earth depofited on the cloth cannot detach itfelf till the 

 cloth is dry. The gray fait of commerce contains in general 

 12'- per cent, of foreign matters, nearly one-half of which is 

 water, and about as much earth. 



This procefs, which on account of its fimplicity I confider 

 as likely to become ufeful for domeftic purpofes, might per- 

 haps be applicable to fait manufactories and fait refineries. 



X. On 



