132 COMMON SALT. 
hot fire, the liquor or brine is boiled until nearly all the 
remaining particles of water have passed off by evapo- 
ration, and nothing is left in the pans but salt. This is 
thrown together into proper vessels, for a few days, to 
drain, after which it is fit for use. 
In some countries the whole evaporation is performed 
by the heat of the sun ; and, in extreme northern cli- 
mates, where the sun would not have sufficient power 
for the operation, a very different process is adopted. 
The water is suffered to freeze in the salterns, and that 
portion of it which continues uncongealed is so strongly 
saturated that it requires only a moderate heat to eva- 
porate the remainder of the water, and to crystallize 
the salt. 
Bay salt is that which is produced from the evapora- 
tion of sea-water by the heat of the sun only. 
The inhabitants of Cardona, in Spain, make of the 
rock salt in their neighbourhood various transparent ar- 
ticles, which they vend at a cheap rate. These, which 
consist of small altars, figures of saints, crosses, chande- 
liers, salt-cellars, &c. are as clear as crystal, and, to ap- 
pearance, as lasting. They are chiefly purchased by 
strangers as curiosities, and are distributed over various 
parts of Spain and the south of France. 
The decomposition of salt furnishes the muriatic acid 
(29), or spirit of salt of commerce. This liquid, which 
is much used in the arts, and is in great request by 
chemists, is prepared, for common purposes, by mixing 
one part of common salt with seven or eight parts of 
clay, and distilling the mixture ; or by distilling com- 
mon salt and spirit of vitriol or sulphuric acid (24), and 
receiving the product into a vessel containing water. 
It has been discovered that muriatic acid, in a state 
of gas, is an excellent means of correcting putrid exha- 
lations. In the year 1773, the cathedral church of Di- 
jon was so much infected by the corruption of bodies 
which had been interred within its walls, that it was en- 
tirely deserted. The professor of Chemistry at Dijon 
having been applied to for assistance, placed, on a few 
