A K T 1 C I> E X . 



On the decomposing power of Wain- at high temperatures, by Richard i. Tilghman. 



Read August 20, 1847. 



It has long been noticed, that partial decomposition is often effected in attempting to 

 render anhydrous, by heat, certain salts which require a comparatively high temperature 

 for the expulsion of their water of crystallization. This effect is not limited to those salts 

 which are capable of decomposition by the action of heat alone, but extends to many 

 which, when previously rendered anhydrous, are entirely unaffected by this agent. The 

 chloride of magnesium offers a striking instance of such an action, being almost entirely 

 reduced to magnesia, with escape of hydrochloric acid, when its solution is evaporated 

 by a strong heat; the anhydrous chloride, when obtained by other processes, is, on the 

 contrary, unaffected by the highest heat. 



Even chloride of calcium, a salt of a much stronger radical base, has been observed to 

 give off a portion of acid, when all its water of crystallization is driven off by a red heal. 

 In these and many other instances, it seems evident that the escaping water of the salt is 

 the actual decomposing agent, and that the intensity of its action depends solely upon 

 the degree of heat which the salt can sustain before giving it off. 



Contact of the salt and water, at high temperatures, appears to be the only requisite 

 of decomposition. It was, therefore, thought probable, that by exposing the salt, even in 

 its anhydrous state, to a high heat, and passing over it a current of aqueous vapour, 

 raised to a similar temperature, not only might the above-mentioned salts be completely 

 decomposed, but also that many others which have hitherto given no such signs of partial 

 decomposition, might be acted upon in a similar manner. 



On making the experiment, it was found, that not only the anhydrous chloride ol 

 calcium, but also the chlorides of strontium and barium could be rapidly decomposed by 

 exposing them, at a high red heat, to a current of steam ; hydrochloric acid was copiously 

 evolved, and escaped alongwith the excess of steam, while the bases of the respective 

 re left in a tree state; the lime remaining anhydrous from the intensity of the heat 

 employed, while the baryta and Btrontia combined with a portion of aqueou vapour, and 

 were found in th< if hydrati . 



VOL. x.— 39 



