^^ DECOMPOSITION OF SULPHATES BY HEAT. 



origin of the columns themselves; and 4thly, The veins of 

 carbonate of lime and zeolite, which are not found here 

 in solitary pieces as in the vicinity of Etna and Vesu- 

 vius, but are ajnid the lavas and in the strata of pumice and 

 tttfa, and are diffused on the lava it&elf, and occasionally 

 crystallized in its cavities. 



Effects of heat 

 on sulphates 

 not such as 

 commonly 

 supposed. 



Roastinj/ of 

 sulphuretted 

 cfes. 



Sulphate of 

 copper maile 

 by roasting tlie 

 tuiphurct. 



VII. 



On the Decomposition of Sulphates hy Heat : by Mr. Gay- 

 LussAC, Member of the Institute*. 



J[^ HE object of Mr. Gay-Lussac, in the paper of which I 

 am about to give an abstract, was to make known the effects 

 of heat on sulphates ; and the experiments he made for this 

 purpose led him to results very different from those, that 

 others hud hastily promulgated on no better ground than 

 probability. Beside extending our chemical knowledge, this 

 paper has the advantage of presenting immediate applications 

 to metallurgy, one of the sciences, to the promotion of which 

 this Journal is devoted. It is in this point of view I shall 

 present the labours of Mr. Gay-Lussac; and, that their ap- 

 plication may be more obvious, I shall take the liberty of 

 making a little change in the order of his experiments. 



He observed the phenomena that accompany the roasting 

 of several metallic sulphurets, as well as the results of that 

 operation : and his experiments farther confirm the opinion, 

 that the formation of sulphates is unavoidable in the roasting 

 of sulphuretted ores ; and that the separation of the sulphur 

 is not complete, till these sulphates have been decomposed. 

 I shall first give his experiments on this subject, and then 

 proceed to the decomposition of the sulphates. 



" I knew," says Mr. Gay-Lussac, " that in several manu- 

 factories sulphate of copper is made by roasting the sulphu- 

 ret in reverberatory furnaces. At Goslar sulphate of zinc is 

 prepared by a similar process. I attempted to imitate this 



* Journal (hs Mine?, vol. XXII, p. 325. Taken from the Mera. of 

 the Socitty of Arcueil, vol. I. 



process 



