176 M. C. Deville on the origin of Granite. 



quartz, corundum, &c. I have simply borrowed the apparatus, 

 and the obliging assistance of that ingenious experimenter. 



2. That where the name of Deville is mentioned a second time, 

 it refers to my brother M. Henri St.-Claire Deville, who has been 

 able to obtain enormous temperatures by other methods than 

 those of M. Gaudin. 



I may be further permitted to mention, in reference to the 

 historical part of the question, that I was the first to show that 

 quartz-glass has a density of 2*22, which is therefore 0*17 lower 

 than that of the crystalline quartz from which it is derived. 



I insist upon this fact ; for it is by no means isolated. For 

 me, its establishment is connected with a series of previous 

 researches on the properties which rocks and silicated minerals 

 acquire when they are melted and then rapidly cooled, but more 

 especially on the properties which sulphur assumes under these 

 conditions. 



Lastly, I believe that these singular properties of quartz, 

 felspar, &c. may have exercised considerable influence on the 

 conditions under which granite is formed, and that, hence, it is 

 necessary to take them into account when the origin of this rock 

 is discussed. 



For some time I have called the attention of scientific men to 

 these peculiar phsenomena of temper, and to the abnormal distri- 

 bution of heat which seems to prevail in the interior of one and 

 the same body. 



The superfused substance holding for a greater or less time a 

 quantity of heat larger than it should normally possess, retains, 

 although in the solid form, the properties of a liquid : in cer- 

 tain cases it retains softness and plasticity, and in all an amor- 

 phous and vitreous structure, a greater solubility, and a less 

 considerable resistance to chemical agents. Another portion 

 (the external pellicle, the tempered exterior) retains, on the con- 

 trary, a lower latent heat, and presents different properties. 



This view, whether it be adopted or not (and there are many 

 facts which might be cited in its support, — the well-known ex- 

 periments of M. Mitscherlich and of M. Regnault, my own 

 researches*, the researches of M. Favref, &c), led me to the 

 discovery of insoluble sulphur. I first prepared this body by 

 the direct tempering of sulphur; and by the application of this 

 principle I was led to think that flour of sulphur being obtained 

 by rapid cooling, and in a minute state of division, must have a 

 larger tempered surface, and consequently the largest quantity 

 of insoluble sulphur, — which was actually found to be the case. 



* Comptes Rendus, vol. xxv. p. 857 ; vol. xxvi. p. 1 16; vol. xxxiv. pp. 534 

 and 561 ; and Annates de Chimie et de Physique, vol. xlvii. p. 94. 

 f Ann. der Pharm. vol. xxiv. p. 344. 



