446 On the Manufacture and Quality of Chefbite Salt. | {June 1, 
Buton adding to it a fingle drop of muri 
#tic-a¢id, afenfible rednefs was given.— 
By the addition of a few drops of a folu- 
tion of carbonate of pstaf to a like folu- 
tion of ftoved-falt, a light green colour 
was given (o the blue juice of vegetables. 
On making fimilar experiments with a 
folution of 480 grains of large grained 
fifhery-(alt, prepared by afi evaporation 
condu@ed at 1z0 degrees of Fahrenheit, 
the refult was the fante, excepting that 
the precipitate, on the addition of the 
jolution of carbonate of potafh, amounted 
to one grain only. 
From the firft experiment it appears, 
that there is a {mall quantity of muriated- 
lime and magnefia cambined with eich 
kind of falt; but that even in the ftoved, 
or the falt pr pared by a boiling-heat, 
thefe do not amount to ,F, patt of the 
miuriate of foda; and in the large-gvained, 
to little more than .3, part. 
The fecord experiment fhews that forne 
folphate of lime is in the falt ; but as this 
is foluble in water only in the proportion 
of 1* {0 500, it is obviogs how fmall the 
quantity of this mutt neceffarily be: and 
* It may here be remarked, that the pro- 
portion of earthy-falts to the muriate of foda, 
is ftiil fmaller in the manufactured-falt than 
in the brine, {mall as it is even in the latter; 
for onthe application of heat to the brine, 
a portion of the acid may be obferved to leave 
the carbonate of lime, and this is no longer 
held in folution; while, as the evaporation 
proceeds, the fulphate of lime fubfides, and 
mixes with the carbonate of lime which has 
been feparated. Thefe earthy-falts are part- 
ly taken out in the early ftage of the procefs 
of manufacture, with a portion of the muri- 
ate of foda firft formed, by the operation of 
“< clearing” the pan; and partly fubfide and 
adhere to the upper furface of the pan, forming 
that incruftation there which is called by the 
workmen ‘¢* panfcratch,’’ or ‘* {cale,” and 
‘which gradually accumulating, it becomes 
neceflury #o remove from the pan every three 
or four weeks by * picking.” 
‘From an analyfis of the ** clearings,” by 
the excellent chemift above-mentioned, Mr. 
William Henry, it appears that 480 parts 
contained 334 0f fhuriate of foda, 20 of carbo- 
nate of lime, and 76 of fulphate of lime.— 
He found 430 parts of the ‘* pickings” to 
cuntain 40of muriate of foda, 60 of carbo- 
nate, and 330 of fulphate of lime. Circum- 
ftances are, of courfe, occurring to vary thefe 
proportions. No muriate of magnefia is 
found in either the ¢learings or pickings, 
fince this, being miuch more ready of folu- 
tion than muriate of foda, remains in the li- 
quor left at the toctom of the pan after the 
sourlate of foda has been drawn out, 
as it has appeared that none fs contained iz 
the rock-{alt, what little there is of it caw 
be derived only from the water of foiu- 
tion, and can contain nd more than thiss 
No one will, J believe, be found to fuf- 
pect that the fmall portion there is of it 
can injure the quality of the falt. 
The tnird experiment fhews, that there 
is not either in the ftoved, or the large- 
grained fithery-falt, any uncombined acid 
or alkali. 
Tt was an idea of the late:Dr. Brown- 
rigg, when he publifhed his imgenious 
and philofophical work om the Manufac- 
ture of common Salt, that by a boiling- 
heat, a portion of the acid in the muriate 
of foda was expelled, and thar the falt pre- 
pared in this procefs had an excels of alka- 
li. The learned Bifhop of Llandaff feems 
to have entertained the fame opinion.~= 
He afcribes the fuppoled fuperiority of 
Dutch falt to the addition of four whey 
which they make to the brine, and 
which, he imagines, unites with any un+ 
combined alkali in it. Tie above expe. 
riment, which was frequently repeated, 
fhews that this 1s not the cafe! It corre- 
fponds with the experiments made by Mr, 
Boyle, and proves that 29 /2paration takes 
place in the component parts of the muriate 
of foda by boiling the brine. 
“The expertments which hayvé been men+ 
tioned, and the flatement of facéts which 
has been given, muft, we prefume, have 
convinced every unprejudiced perfon that 
the ialt manufafured ain Chefhire ts almoft 
entirely free from any foreign contents, 
and that it conifts of pure muriate of fe-~ 
da, with fearcely any other falme or 
earthy addition. But, though more pure 
than any other falt manufactured, it does 
not neceflirily follow, that, in ewery form 
in which it is prepared, it fhould poffels 
{uperior advantages in the preferyation of 
animal_food, fince feveral other circum. 
ftances are here to be taken into confide. 
ration. Thele will be belt underftood by 
examining what is the procels of nature 
in forming the cryftals of muriate of 
foda’; and by ttating the different ways in 
which the manufacture is conducted in 
Chethire. ; . 
The natural form of the cryftals of 
muriate of foda, is that of a perfect cube; 
and they regularly affume this figure, 
when the due arrangement of their par- 
ticles has not been interrupted by agita- 
tion, or the application of ftrong heat.— 
«¢ ‘Thefe cubes exhibit diagonal firze, and 
frequently, on each fide, protiuce fquares 
parallel to the external furface, gradually 
decreafing inwards, circumftances ey 
ew 
