SALTS OF MAGNESIA. 507 



sulphuric acid. The mixt sulphates are easily separated, that 

 of lime being soluble to a small extent only, while that of mag- 

 nesia is highly soluble in water. A solution of sulphate of lime 

 is also decomposed by carbonate of magnesia,, with the forma- 

 tion of sulphate of magnesia, and this reaction is often witnessed 

 in beds of magnesian limestone, when water containing sul- 

 phate of lime, percolates through them. 



The crystals of sulphate of magnesia are four-sided rectangular 

 prisms, which when pure, have a slight disposition to effloresce 

 in dry air. One hundred parts of water at 32 dissolve 25.76 

 parts of the anhydrous salt, and for every degree above that 

 temperature, they take up 0.26564 part additional, (see Gay- 

 Lussac's table of the solubility of salts, at page 182). The 

 solution has a bitter disagreeable taste, which is characteristic 

 of all the soluble salts of magnesia. It is not precipitated in 

 the cold by the alkaline bicarbonates, by common carbonate of 

 ammonia, nor by oxalate of ammonia if the solution of sul- 

 phate of magnesia be dilute. 



Sulphate of magnesia loses 6HO considerably under SCO , 

 but retains 1 eq. even at 400. The last equivalent is replaced 

 by sulphate of potash, forming the double sulphate of mag- 

 nesia and potash, which is considerably less soluble than the 

 sulphate of magnesia, and crystallizes with 6HO. Sulphate of 

 magnesia unites directly with sulphate of ammonia also, when 

 solutions of the salts are used, but not with sulphate of soda. A 

 double sulphate of magnesia and soda occurs, however, in the 

 manufacture of sulphate of magnesia, which is said to have 

 6 HO, like the potash salt, but a different form. 



Sulphate of magnesia, when ignited in contact with charcoal, 

 leaves a sulphuret of the metal., but it is the last of the earths 

 which exhibits this analogy to the alkalies. The sulphuret of 

 magnesium is soluble in water. It may likewise be obtained 

 by precipitating sulphate of magnesia by sulphuret of barium. 



Hyposulphate of magnesia forms crystals, which are persis- 

 tent in air, very soluble, and contain 36.77 per cent, or 6 

 atoms of water of crystallization, like the following salt. 



Nitrate of magnesia is a very soluble and highly deliquescent 

 salt. It crystallizes with 6 HO, five of which it loses at a high 

 temperature. The remaining hydrate may be fused without 

 decomposition, but when heated more strongly, it loses both 

 nitric acid and water, and pure magnesia is left. It appears 



