British and Foreign Salt, 1 13 



Some estimate of its general proportion, when ascertained 

 on a larger scale, may be formed from the fact that Go- 

 vernment, in levying the duties, allows 65lb. to the. bushel 

 of rock salt, instead of 56lb., the usual weight of a bushel 

 of salt. 



III. The earthy muriates, and especially that with base 

 of magnesia, abound most in salt which is prepared by the 

 rapid evaporation of sea water. Now since common salt, 

 in all its forms, contains, as will afterwards appear, very 

 little water of crystallization, it is probable that the muriate 

 of magnesia, discovered by the analysis of sea salt, is de- 

 rived entirely from that portion of the mother liquor 

 which adheres to the salt after being drained, and which 

 amounts to about one-seventh of its weight. The larger 

 the size of the grain, the less is the quantity of this solu- 

 tion 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 

 the crystals 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 evaporation advances. 



In the several varieties of Cheshire salt, the earthy mu- 

 riates 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 ob- 

 tained by evaporating to dryness the whole of a portion of 

 Cheshire brine, does not give more than five parts of earthy 

 muriates in 1000. In the entire salt of sea water, accord- 

 ing to Bergman, the earthy muriates form no less than 213 

 parts in the same quantity. 



According to the proportion in which the earthy mu- 

 riates are present in any kind of salt, will be its power of 

 deliquescence, or of attracting moisture from the atmo- 

 sphere. It is not entirely, however, from the salts with 

 earthy base that common salt derives this quality ; for the 

 most transparent specimens of rock salt, which I find to 



Vol. 36. No. 148. slugtist 1810. H consist 



