99 
of British and Foreign Salt. 
forms, contains as will afterwards appear, very little water of 
crystallization, it is probable that the muriate of magnesia, dis- 
covered by the analysis of sea salt, is derived entirely from 
that portion of the mother liquor, which adheres to the salt 
after being drained, and which amounts to about ~ of its 
weight. The larger the size of the grain, the less is the quan- 
tity of this solution which the salt holds suspended, and hence 
the salt prepared at a lower degree of heat, being in larger 
crystals, is less debased by the magnesian muriate, than the 
salt formed at a boiling temperature. It is probable, also, that 
when the salt is drawn at intervals from the boiler, the pro- 
portion of the earthy muriate will vary with the period of the 
evaporation, at which it is removed. For it may readily be 
conceived, that as the proportion of the earthy muriates in any 
brine is increased by the separation of muriate of soda, the 
greater will be the quantity of the muriates which themrystals 
of common salt, formed in the midst of the brine, will retain ; 
thence it follows, that, so far as the earthy muriates only are 
concerned, salt must diminish in purity as the process of eva- 
poration advances. 
In the several varieties of Cheshire salt, the earthy muriates 
do not exceed one thousandth part of this weight, and they 
are precisely, (or so nearly so, that the difference is not 
ascertainable) the same in all. This will cease to be matter 
of surprise, when it is considered that the salt obtained by 
evaporating to dryness the whole of a portion of Cheshire 
brine, does not give more than g parts of earthy muriates in 
1000. In the entire salt of sea water, according to Bergman, 
the earthy muriates form no less than 213 parts in the same 
quantity. 
O 2 
