1804.) On the Manufadture and Duality of Chefpire Salt. 
fhew the veltiges of their internal ftruc- 
ture ; for every cube is compofed of fix 
quadrangular hollow pyramids, joined by 
their apices and external furface Each of 
thefe pyramidsis filled up by others fimilar, 
but gradually decreafing; and them the 
form is completed. By a due degree of 
€vaporation, it :is no difficult matter to 
obtain thele pyramids feparate and difting, 
or fix of fuch, either hollow, or more.or 
lefs folid, joined toge' her round acenter.”’ 
~—* If we examine the hollow pyramid* 
of falt feparately, we fhall find it com. 
pofed of four triangles, and,each of thefe 
formed of threads parallel to the bale; 
which threads, upon accurate examina- 
tion, are found to be nothing .more than 
deries.ot {mall cubes.’’+ 
The pertect jery(talization of the falt 
can, however, take place only under 
the cireumitances . above mentioned, a 
freedom from agitation, and from too ra- 
pid «an evaporaiion of the water which 
holds the fait-in folution ; and ijt is princi- 
pally on the prefence oy abfence.ot thefe 
eaufes that the variation in the, appearance 
of the falt manutadtured in Chefhire de- 
pends. 
The manufa&ure is condu&ed in three 
different ways, or, rather, heat.is applied 
in three diflerent. degrees, to effect the 
evaporation of the water of folurion. 
‘. In-making the foved, or lump-falt, 
2S it.is calied, the brine ts brought to.a 
beiling-heat, (which, in brine fully fatu- 
sated, is 226 .0f Fabyenheit,) and it is 
continued nearly at this heat during the 
formation of the falt. The little chryftal 
ts no fooner formed, than, by the agitation 
of the brine, it fubfides to the bottum of 
the pan. If taken out, it apperrs, at fit 
&ght, to be granular, or a little flaky ; 
but, if more accurately examined, it is 
Found to approach to the form of a little 
quadrangular, though fomewhat irregu- 
lar, pyramid. 
2. In making the common falt, the 
_ghryftaliization is carried on with the brine 
heated to 160 or 170 degrees of Fahren- 
* The bafes and altitudes of thefe little 
pyramids are in general equal ; thus fhew- 
ing the difpofition of the talt to form a 
cube, 
» F See Bergman’s Effays, vol. ii. p. 12, 
33. | 
- ~ The falt thus made, being afterwards. 
dried in heated ftoves, lofes about one- 
feventh of its weight by the evaporation of a 
portion of its water of cryftallization, 
47 
heit. The falt formed in this procefs is 
in quadrangular pyramids or hoppers, 
clofe and compact in their texture, fre- 
quently cluttered together, and larger or 
{maller, accorcing to the degree of heat 
which has been applied. Litcle cubical 
cryftals will often be intermixed with, 
and attached to, thefe. 
he HO) make the large-grained, or fibery- 
felt, the bring is brought toa heat from 
roo to 110 of Fahrenheit ; and at this 
heat the evaporation of the water and 
the cryftallization of the {alt proceed.— 
Wo agitation is produced by it on the 
brine ; and the flowneis of the cvapora- 
tion ailows the muriate of toda to form in 
large, nearly cubical,’ cryftals, fcldom, 
however, quite perfect. 
Though the outward form of the falt 
produced by thefe varied procefits is very 
diffimilar, there is {careely any difference, 
as has appeared by the experiments 
which have been given, in its degree of 
purity. Indeed, the different proceffes, 
infiead of being regarded as diftin ones, 
might, perhaps with more propriety, be 
confidered as gradations inthe fame pro- 
cefs, interrupted only by the agitation 
which the heat gives to the brine. 
the ftoved-falt, where the agitation is 
greateft, only a {mall portion of the little 
pyramid has been formed. In the com- 
mon-falt, the heat and agitation during 
the cryltallization, beng lels, the hollow 
pyramid is completed. In making the 
large-grained fifhery-{alt, there being no 
agitation, the little pyramids are enabled 
to unite, and to form into cubes. 
That thefe are faéts, is readily proved 
by rediffolving the large-grained fifhery. 
falt, and applying a boiling-heat to the 
brine thus made. We then procure a eras 
nular or flaky falt, refembling the ftoved- 
falt; while, on the other hand, if we 
rediffolve the ftoved-falt, and evaporate 
the water of foiution at a heat of roo 
degrees, we hall procure large cubical 
cryftals of muriate ot foda. 
Since, from the experiments which 
have been mentioned, and the detail of 
facts which has been given, it is evident 
that the /alt manufaétured in Chefhire is 
procured from fources much purer than 
bay-falt, or than falt of any other manu- 
facture : fince it has appeared that it is an 
almoft pure muriate of foda, and has 
fearcely any admixture of, earthy-falts < 
fince the falt made by the different pro- 
cefles,.and the application of varied de- 
grees of heat, differs only in outward: 
Ay . ie ae 
Tn. 
