SALTS SLPHATES. 33 1 



(c.) Frequently confounded with sulphate of baryta, but easily 

 distinguished from it, by its sp. gr. which is 3.85 ; it is always below 

 4. and sulphate of baryta always above 4.25 



3. PREPARATION. 



(a.) By mingling sulphuric acid and strontian water, when it is 

 precipitated in the form of a white and tasteless powder. 



(b.) Or by mixing any soluble form of strontia, with any soluble 

 sulphate. 



4. PROPERTIES. 



(a.) Tasteless and inodorous ; nearly insoluble; requiring 3000 

 or 4000 parts of cold, or 3840 of boiling water. 



(b.) Dissolved in boiling sulphuric acid, and thrown down again 

 by water ; or in the additional mode named under sulphate of baryta, 

 4. (c.) note. 



5. COMPOSITION. 



Acid, 42 4- earth 58=1 00. Wollaston. 



" 46 -f " 54=100. Fauquelin. 



43 4- " 57 = 100. Stromeyer. 



According to Dr. Thomson, it is composed of 1 proportion of 

 strontia 52, and one of acid 40=92 for its equivalent, and this would 

 require this salt to consist of 43.47 acid, and 56.53 base. 



6. DECOMPOSITION. 



(a.) JVb acid decomposes it,* nor does air affect it. At a high 

 temperature it melts. 



(b.) JVb base except baryta can separate its acid; but carbonates of 

 the fixed alkalies decompose it with the aid of heat. 



(c.) Decomposed by ignition with charcoal, in the same manner 

 as sulphate of baryta is. It has not been applied to any use.f 



SULPHATE OF MAGNESIA. 



1. NAME AND PREPARATION. 



(a.) That of the shops, called Epsom Salts, from a mineral 

 spring at Epsom, in Surrey, (Eng.) where, mixed with some sulphate 

 of soda, it was first obtained by Dr. Grew, A. D. 1675. But Dr. 

 Black first distinguished it from Glauber's salt, with which it had, till 

 his time, been confounded. 



(b) Formed, by dissolving the carbonate of magnesia, or calcined 

 magnesia, in sulphuric acid, somewhat diluted ; it is then evaporated 

 and crystallized. 



(c.) Strong sulphuric acid and calcined magnesia, produce great 

 heat, and sometimes light ; but this acid evolves no heat with the 

 carbonate, because the gas carries it away. 



* The phosphoric and boracic effect its decomposition, if aided by a red heat* 

 Fourcroy, Vol. Ill, p. 48. 



t Except in pyrotechny, for preparing the nitrate of strontia an ingredient of red 

 re.-3. T. 



