234 AN ANALYSIS 



The difficulties attending the perfect separation of com- 

 pound salts from each other, by crystallization, even with the 



aid 



edges, considering the rhomb as a four-sided prism, and transparent. The cry- 

 stals are permanent in the air ; they are soluble in little more than three times 

 their weight of water, at the temperature of 60° ; they do not undergo the 

 watery fusion from heat, but suffer decrepitation. In these properties, this salt 

 diifers entirely from sulphate of soda, or sulphate of magnesia. 



To determine its composition, 20 grains reduced to powder were exposed 

 to heat, raised gradually nearly to redness ; they lost from the escape of water 

 5.6 grains. The residual powder was dissolved in water, and muriate of ba- 

 rytes was added as long as any precipitation was produced. The precipitate 

 dried at a red heat, weighed 23.9 grains, equivalent to sulphuric acid 8.2 

 grains. To the clear liquor carbonate of ammonia was added, which did not 

 impair the transparency ; phosphoric acid was then dropped in, which produ- 

 ced a copious precipitation. The precipitate, calcined at a red-heat, weighed 

 5.3 grains, equivalent to 2.1 of magnesia, or 6.4 of sulphate of magnesia; 

 the residual liquor being evaporated to dryness, the dry mass was submitted 

 to heat, gradually raised, as long as any vapours exhaled ; it afforded, by solu- 

 tion in water and evaporation, muriate of soda in cubes, which, after expo- 

 sure to a red heat, weighed 6.4 grains, equivalent to 7.8 grains of sulphate of 

 soda. 100 grains of the salt, therefore, afford of 



Sulphate of Magnesia, - 32 grains. 



Soda, - 39 



Water of Crystallization, - 28 



Loss, 1 



100 



It afforded also a slight trace of muriatic acid ; its solution being in a very 

 slight degree rendered turbid by nitrate of silver, probably owing to the inter- 

 mixture of a little muriate of soda, as an extraneous ingredient. This ac- 

 counts for the proportion of sulphuric acid, as inferred from the quantities of 

 the bases, being a little larger than that directly obtained by the precipitation by 

 muriate of barytes. 



The difference of crystalline form, as well as other differences of proper- 

 ties in the salt from those, either of sulphate of soda or sulphate of magnesia, 

 sufficiently prove that it is not merely an intermixture of the two, but that it 

 is of definite composition. It deserves to be remarked, too, that it has not 

 the same relation to water that either of these salts has, or any mean be- 



tween 



