ANALYSIS OF BRITISH AND FOREIGN SALT. 199 



the less is the quantity 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 mag- 

 nesian muriate, than the salt formed at a boiling- tempera- 

 ture. Tt is probable also, that, when the salt is drawn at 

 intervals from the boiler, the proportion of the earthy mu- 

 riate 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 these muriates, which the crystals of common 

 salt, formed in the midst of the brine, will retain. It fol- 

 lows therefore, 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 muri- Cheshire salt, 

 ates do not exceed one thousandth part of their 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 5 parts of earthy muriates in 

 1000. In the entire salt of seawater, according to Bergman, 

 the earthy muriates form no less than 213 parts in the same 

 quantity. 



According to the proportion in which the earthy muriates Pure muriate 



are present in any kind of salt, will be its power of deiiques- of s . oda attract * 



„ • /. i i . moisture, 



ceuce, or of attracting moisture from the atmosphere. It is 



not entirely, however, from the salts with earthy base, that 

 common salt derives this quality; for the most transparent 

 specimens of rock silt, which I find to consist of absolutely 

 pure muriate of soda, attract much moisture from a humid 

 atmosphere. 



IV. The sulphate of magnesia and the sulphate of lime Earthy sul. 

 both enter into the com position of all the varieties of salt phates. 

 prepared from seawater; but the sulphate of lime alone is 

 found in Cheshire salt. The proportion of sulphate of mag- 

 nesia is greatest in that variety of seasalt, which has been 

 formed by rapid evaporation. In foreign bay salt, its quan- 

 tity is very insignificant. 



From 



