PERMEABILITY OF HIGHLY-HEATED IRON BY GASES. 279 



Remarks on the preceding by M. H. Sainte-Claibb Deville, 



I have nothing to add tp the very interesting and conclusive note of M. 

 tJailletet. I wish merely to call his attention to another phenomenon which ig 

 frequently observed in metallurgic operations, namely, the disengagement at a 

 high temperature of gases held in solution by liquids. The ebullition of silver 

 and of litharge, so thoroughly investigated by M. Le Blanc, and the disengage- 

 ment of bubbles of inflammable gas from the interior of vitreous masses, are 

 phenomena which can be generalised with certainty. White iron and steel, at 

 the moment of cooling, allow the escape of a gas (doubtless carbonic oxyde or 

 hydrogen) which is highly injurious to the perfection of pieces run into cast- 

 steel ; and with this phenomenon we may connect some very curious observa- 

 tions of Messrs. R6sal and Minari, on the production of scoriae caused by bub- 

 bles of inflammable gas on the surface of white iron in fusion (or rather in 

 the process of solidification), while it is very curious that the grey iron has 

 nothing of the kind. It.i3 easy to trace the origin of these combustible gases 

 to the heating furnase, the walls of the crucibles permitting the surrounding 

 •gases by endosmose jto concentrate upon the included materials. It would be 

 very desirable that experiments should be made in the large metallurgic estab- 

 lishments where engineers have at their disposal scientific instruments, which 

 become more precious in proportion as they know how to avail themselves of 

 them, as M. Cailletet has well shown. 



The experiment of M. Cailletet, combined with that which M. Troost and my- 

 self have published on the porosity of platinum, explains the formation of 

 bubbles which often injure the quality of that metal, for these bubbles are formed 

 only when platinum in plates is raised to a high temperature, and their develop- 

 ment does not depend on the expansion of the air which we might suppose in- 

 terposed between the metallic leaves which form the boundaries. 



Note on the preceding communications, by M. Ch. Sainte-Claiee Deville. 



The curious experiment of M. Cailletet, as well as those recorded in the me- 

 moirs presented recently to the Academy by my brother and M. Troost, prove 

 incontestably that the metals, platinum and iron, possess the property of per- 

 meability by gases when raised to bright incandesence. On the other hand, the 

 researches of> the two last-named philosophers prove that, while hydrogen tra- 

 verses easily a tube of porcelain highly heated but not modified in structure, 

 this is no longer the case when the temperature of the tube is raised to the 

 point capable of softening or vitrifying its exterior wall. In this case, not only 

 does the gas cease to traverse the tube, but it is stopped and partly absorbed by- 

 the vitrified surface, which again sets it free on recovering its porous structure. 

 These different facts are connected with the antagonistic properties which dis- 

 tinguish the crystalline from the vitreous or amorphous condition. I have dis- 

 cussed the subject several times since the year 1845, and propose shortly to 

 recur to it with some detail, attaching it to the more general fact of allotropy, 

 ^f which it is only a particular case. At present I desire merely to call atten- 

 tion to the geological interest of the question, following out the train of reflec- 

 tion my brother has presented, and remarking some complimentary expressions 

 to myself with which he has accompanied his last communication. 



