14 THE CANADIAN NATURALIST. [Feb. 



with common salt ; and by reducing the temperature to 6° C.,. 

 a large portion of pure sulphate of magnesia now crystallizes 

 out. The farther evaporation of the remaining liquor by the heat 

 of summer causes the potassium-salt to separate in the form 

 of a hydrous double chlorid of potassium and magnesium, an 

 artificial carnallite.* 



By varying somewhat the conditions of temperature, the sulphate 

 of magnesia and the chlorid of sodium of the mother-liquor undergo 

 mutual decomposition, with the production of sulphate of soda 

 and chlorid of magnesium. Hydrated sulphate of soda crystallizes 

 out from such a mixed solution at 0° C, and by reducing the 

 temperature to — 18° C. the greater part of the sulphates may be 

 separated in this form from the mother-liquor of 1.24, previously 

 diluted with one tenth of water ; without which addition a mix- 

 ture of hydrated chlorid of sodium would separate at the same 

 time. If, on the other hand, the temperature of the mixed solu- 

 tion be raised above 50° C, the sulphate of soda crystallizes out in 

 the anhydrous form, as thenardite. By the spontaneous evapora- 

 tion during the heats of summer of the mother-liquors of density 

 1.35, a double sulphate of potassium and magnesium separates. 

 These reactions are taken advantage of on a great scale in Balard's 

 process, as modified by Merle, f for extracting salts from sea-water. 



§ 23. The results of the evaporation of sea-water would however 

 be widely different if an excess of lime-salt were present. In this 

 case the whole of the sulphates present would be deposited in the 

 form of gypsum at an early stage of the evaporation, and the 

 mother-liquor, after the separation of the greater part of the 

 common salt, would contain little else than the chlorids of sodium, 

 potassium, calcium, and magnesium. 



* The hydrous double chlorid of potassium and magnesium (carnal- 

 lite of H. Rose) occurs in large quantities in a stratum of clay overlying 

 a great bed of rock-salt 100 feet thick, at Stassfurth in Prussia. It is 

 associated with considerable quantities of sulphate of magnesia. 

 According to Clemm, this sulphate of magnesia, to which the name of 

 kieserite has been given, and which occurs also in Anhalt, contains but 

 one equivalent of water, (MgO,S0 3 +HO). It is not more soluble 

 than gypsum, and unlike the ordinary sulphate of magnesia, loses 

 the whole of its acid at a red heat in a current of steam, the acid 

 passing off undecomposed. This salt is found in such large quantities 

 as to be of economic importance. (Bull, Soc. Chim. de Paris, 1864, p. 297.) 



f See my paper in Silliman's Journal [2] xxv. 361 ; also Report of 

 the Juries of the Exhibition of 1862, class ii, p. 48. 



