242 AN ANALYSIS 



of muriate of lime, but in all of them with sulphate of lime 

 considerable quantities of sulphate of magnesia. In the latter, 

 therefore, the muriate of lime had been converted entirely into 

 sulphate of lime from the excess of sulphate of magnesia ; in 

 the former, from the deficiency of the sulphate, a portion of 

 the muriate of lime had remained undecomposed. 



A result somewhat similar, and which affords a very direct 

 application of the same principles, is stated by Mr Horner, in 

 his analysis of the salt-brine at Droitwich, compared with that 

 of Cheshire *. The latter contains a little muriate of lime ; 

 the former contains none. But, then, that of Droitwich con- 

 tains sulphate of soda and sulphate of lime ; there is every pro- 

 bability, therefore, that its muriate of lime has been converted 

 into sulphate of lime by the sulphate of soda, which is in ex- 

 cess ; while in the Cheshire brine, as there is no sulphate of 

 soda in excess, that is, none after the evaporation, a portion of 

 muriate of lime remains. 



There is a singular fact stated by Dr Henry with regard to 

 what is called fishery salt, prepared from salt brine, which 

 seems to admit of explanation only on these views. He found 

 the proportion of sulphate of lime mixed with it to be less, as it 

 was collected at a later period of the evaporation ; that drawn 

 from the boiler, after two hours application of the heat, con- 

 tained in 100 parts 16 of sulphate of lime ; that, after 4 hours, 

 contained only 11 ; and that, after 6 hours, only 3£. Now if 

 the water of this brine held sulphate of lime in solution, the 

 sulphate would begin to be deposited when the quantity of 

 water was diminished to that extent that it was unable to re- 

 tain the whole dissolved ; and, in the progress of the evapora- 

 tion, would continue to be deposited proportional to this, 



to 



* Geological Transactions, vol. ii. 



