216 Notes and Memoranda. 



Pebmeability op Metals at High Tempebatubes. — M. L. Cailletefc has 

 made the following communication to the French Academy. After remarking 

 upon the facts mentioned by MM. H. St. Claire Deville and Troost, who found 

 that iron at a high temperature was completely permeable for oxygen, and that a 

 tube, heated in a furnace, and filled with hydrogen, allowed that gas to escape so 

 that a vacuum was formed, M. Cailletet proceeds to detail his own experiments. 

 He says — " I passed portions of a gun-barrel through rollers till they were 

 flattened. The ends were then welded (soudees). Thus rectangular pieces of iron 

 were obtained, formed of two plates in contact, and sealed at their extremities. 

 On strongly heating one of these pieces in a furnace, the non-welded portions 

 separated, and resumed the cylindrical form and their original volume. It could 

 not, therefore, be doubted that the gases of the furnace had penetrated the mass 

 of iron and distended its walls." To a similar action Mr. Cailletet ascribes the 

 cavities in large masses of forged iron ; and he states that in the process of cemen- 

 tation, acier poule, or steel with vesicles, is constantly produced ; but if soft, per- 

 ferfectly homogeneous iron, such as can be obtained by keeping melted steel for 

 several hours at a high temperature, . be employed, it is reconverted into steel 

 without blisters. M. H. St. Claire Deville remai-ks upon this communication that 

 it is "very interesting and conclusive," and he adverts to the discharge of gas 

 from molten matter often observed in metallurgical operations. These gases, he 

 considers, penetrate the walls of the crucibles by endosmose, and give rise to 

 bubbles in the metals. 



Action of Poecelain and Lavas at High Tempebatttbes on Gases- 

 Possible Action of the Moon. — M. Ch. St. Claire Deville makes allusion to 

 the preceding facts, and states that his brother and M. Troost have shown that if 

 hydrogen traverses without difficulty the walls of a porcelain tube at a high 

 temperature, it does not do so when the tube begins to soften or vitrify. The gas 

 is then absorbed by the vitrified surface, from whence it escapes, leaving it porous. 

 He connects these facts with the appearance of certain lavas. He says the lavas of 

 Vesuvius, whatever the rate of their cooling, are always crystalline, and that they 

 disengage aqueous vapour, chlorides, sulphides, etc., as the crystallization pro- 

 ceeds, just as oxygen escapes from silver that takes the rocky form, or air escapes 

 from freezing water. The crystallization of lavas ho states to be accompanied by 

 increase of density and evolution of heat. He traces a resemblance between the 

 Campi Phlegran and the surfaco of the moon, and considers that the latter may 

 have behaved like eruptive matter with excess of silica, which has a tendency to 

 consolidate in a vitreous form, and imprisons gaseous matter in its solidification. 



M. Vial's Pbocess of Engeaving.— The lines are drawn on steel with a 

 fatty ink, or transferred to the steel, which is then plunged in a bath, saturated 

 witli sulphate of copper, and accidulated with 1 nitric acid. In five minutes the 

 plate is removed and washed ; the copper is removed with ammonia, and the 

 engraving is finished. The explanation is that the metallic solution deposits 

 copper on those parts of the plate which are not covered with ink. This copper 

 is removed by the final washing. The acid penetrates the ink slowly, and when 

 this is accomplished a galvanic circuit is completed between tho deposited copper 

 and the steel, protected by the ink from tho siinplo deposition. The steel becomes 

 the positive pole, and is attacked by tho sulphuric acid liberated from the copper 

 by the free nitric acid. M. Vial states that this action is strongest where tho ink 

 U thickest, and that lines are thus etched of tho proper depth and thickness. The 

 copper that results from the electro-chemical decomposition is said to ho thrown 

 down on the borders of the lines, and to lift up tho ink so as to form tho pattern 

 in raised copper, which is removed by the ammonia. Tho process was favourably 

 reported on by a OoBU&istiOD of the French Academy ; and when recently 

 exhibited at tho Society of Arts, hmno practical engravers present thought it 

 would bo adapted to the cheap and convenient reproduction of elfocts not requiring 

 the aid of shading in cross linen. 



