84 Mr Rose on the Composition of 



almost always from the sole cause that the salts are not then 

 equally soluble. A mixture of common salt and sulphate of 

 magnesia exhibits in this view the most extraordinary anomalies. 

 If both be dissolved in a sufficient quantity of water, and if 

 then, at the ordinary temperature, at least in summer, the water 

 of solution be evaporated, the sulphate of magnesia and common 

 salt are deposited. If the solution contain a large proportion of 

 the latter and but little of the former, a part of the common salt 

 is first deposited, then the other, while common salt still remains 

 in solution ; because in the heat of summer the sulphate of 

 magnesia is to a very shght degree more difficult of solution than 

 common salt. If the temperature descends to the freezing point, 

 or ascends beyond 122° of Fahr., in both cases sulphate of soda 

 is deposited, and it is formed from chloride of magnesia, because at 

 the freezing point the sulphate of soda is, of the four salts which 

 can be contained in the solution, viz. common salt, sulphate of 

 magnesia, sulphate of soda, and chloride of magnesia, the most 

 difficult to dissolve, and because at about 122° Fahr. it sepa- 

 rates itself as an anhydrous salt. There is, therefore, ground 

 for supposing that at the ordinary temperature the sulphate of 

 magnesia and common salt simultaneously exist. 



It was from these considerations that Mr Rose was induced 

 in his indication of the constituent parts of the water of Lake 

 Elton, to admit the combination with the magnesia of the whole 

 quantity of the sulphuric acid which he had found, although 

 this was in opposition to the opinion of Murray, which had also 

 been adopted by Dr Marcet. And if some chemists in the 

 analysis of sea-water by the manner of evaporation, and by 

 treatment with alcohol, have discovered sulphate of soda, this is 

 incontestably owing to the circumstance, that, in effecting the 

 evaporation, they had employed a heat reaching almost to that 

 of ebullition. Those who conduct the evaporation of this water 

 at a temperature below 122°, cannot obtain any sulphate of 

 soda. 



As to the specific gravity of sea water, and the proportion of 

 solid matter it contains, they both appear to be very variable. 

 M. de Humboldt is the first who has attracted attention to 

 these points ; and he reckons that the proportion of soli^ parts 

 -varies from 3,^2 to 3,87 per cent. Of recent researches, those 



