436 COMPOUND SALTS 



10. Potash-sulphate of copper. This salt crys- 

 tajlizes in blue coloured rhomboids, with angles 

 of 82 30', and 97 30'. It suffers no change 

 by exposure to the air : its specific gravity is 

 2'116. According to the analysis of Vogel of 

 Bareuth, which was confirmed in my laboratory, 

 its constituents are 



1 atom sulphate of potash 

 1 atom sulphate of copper 

 6 atoms water 



2775 



1 1- P tasn - car bonate of magnesia. When a 

 magnesia, solution of bicarbonate of potash is poured into 

 a solution of muriate of magnesia, both in the 

 atomic proportions, no precipitate appears at 

 first, but in about twenty-four hours there is a 

 deposite of irregular crystals in groups, which 

 constitute a compound salt. When put into the 

 mouth it appears at first tasteless, but speedily 

 gives an alkaline impression ; when cold water 

 is poured on it, the crystals gradually fall to 

 powder, bicarbonate of potash is dissolved, and 

 carbonate of magnesia remains undissolved. 

 When heat is applied to this salt, it gives out 

 water and becomes opaque. If the heat be still 

 farther elevated, carbonic acid gas is driven off, 

 and at a red heat a semifusion takes place. This 

 salt, which is apt to form in chemical analyses of 

 magnesian minerals, has been very carefully 



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