No. 200.] 
33 
may be a fraudulent operation, unless great care is taken in again re- 
moving it by the pans with which the kettles are supplied. 
The correctness of these views will be evident, upon a recurrence to 
the changes which the addition of lime causes in the composition of the 
brine. The excess of carbonic acid which holds in solution the carbo- 
nate of lime and oxide of iron in the raw brine, combines with the added 
lime, and causes a deposit of the whole insoluble carbonate. More- 
over, the lime decomposes the chloride of magnesium, and there result 
chloride of calcium held in solution, and magnesia precipitated. The 
chloride of calcium thus formed, as well as the amount originally con- 
tained in the brine, may be further decomposed by the employment of 
sulphate of soda, which produces sulphate of lime, presently thrown 
down, and leaves the salt in a nearly pure form. And if this salt, the 
sulphate of soda, could be obtained at as cheap a mte as it is in some 
parts of the world, it could no doubt be advantageously employed for 
this purpose. 
It seems to me, therefore, that there can be no good objection to the 
use of lime if it be confined to the reservoirs, as it causes the more 
speedy separation of the earthy matters, and renders the subsequent 
salting more rapid and perfect. But I would repeat, that in order to se- 
cure its beneficial effect, the lime should be in as caustic or pure a state 
as it can be conveniently obtained. Lime which has been air slacked, 
or which has been previously used in a similar operation, cannot be ad- 
vantageously employed: indeed it answers no better purpose than so 
much sand or clay. And with regard to the addition of this substance 
to the brine while boiling, I can only say, that if the resulting earthy 
matters be carefully removed, its use may be tolerated j but it cannot 
be concealed, that in such cases there is a strong temptation to hurry the 
process to completion, and thus to mix up the earthy ingredients with 
the salt. 
All these difficulties are avoided in the mode of manufacturing salt by 
solar evaporation, and by the application of a moderate degree of heat to 
large shallow pans containing purified brine. In the former case the 
impurities subside in separate vats, after which the brine, thus purified, 
is drawn off into another tier of vats in which the crystallization of the 
salt takes place. This salt is in large, hard and white crystals which 
suffer little change by exposure to the air: it is the purest salt that can 
be manufactured, as will be seen by inspecting the table of the compo- 
sition of different varieties herewith presented. 
[Assem. No. 200.] 5 
