414 Intelligence and Miscellaneous Articles. 



times that of the metal. Submitted, at a dull-red heat, to the action 

 of a current of hydrogen, it reabsorbs a volume sensibly equal to 

 that which it had discharged. The metal is again pyrophoric after 

 the hydrogen is expelled. 



II. Cobalt. — An ingot, cast in lime, of pure cobalt was submitted 

 to a red heat for twenty-four hours in a current of hydrogen, and 

 then cooled slowly in that gas. The volume of hydrogen extracted 

 from it in vacuo at a red heat was only one tenth of that of the metal. 



Laminae of cobalt, obtained by galvanic decomposition of the 

 double sulphate of cobalt and ammonia, were heated in vacuo to 200°. 

 They gave up thirty-five times their volume of hydrogen*. Heated 

 subsequently in a current of hydrogen to about 200°, and again 

 cooled slowly in the same gas, they absorbed twenty-four times their 

 volume of it, which they set free again in vacuo at 200°. The same 

 laminae, placed during twenty-four hours at the negative pole of a 

 voltameter, absorbed seven times their volume of hydrogen. 



Pyrophoric cobalt loses its hydrogen in vacuo still more readily 

 than nickel. Instead of making a vacuum, the condensed gas can 

 be expelled by putting the metal into a small balloon furnished with 

 a discharge -tube and filled with water exhausted of air. Heated 

 to 100°, all the gas is disengaged in a few hours. The volume of 

 the gas thus collected is about one hundred times that of the metal ; 

 the cobalt, too, is again pyrophoric after complete expulsion of the 

 hydrogen. Submitted at a dull red heat to the action of a current 

 of hydrogen, it reabsorbs a volume equal to that which it has set free. 



III. Iron. — We have previously proved f that 1 kilogramme of 

 soft iron in the form of an ingot can dissolve at about 800°, and 

 afterwards set free in vacuo at the same temperature, 20 cubic cen- 

 tims. of hydrogen, or one sixth of its own volume. Under the same 

 conditions 1 kilogramme of grey pig-iron, wood-cast, dissolves 88 

 cubic centims. of hydrogen, or more than the half of its volume J. 



It is known that the iron obtained in decomposing by the pile 

 chloride of iron in the presence of sal ammoniac, when plunged 

 into hot water disengages hydrogen and at the same time a small 

 , quantity of ammonia, as was proved by MM. Meidinger§ and 

 Kroemer||. M. Cailletet^f has recently obtained in this way a 

 volume of hydrogen equal to 260 times that of the metal. 



* Analysis of the gas did not show any sensible quantity of nitrogen. 

 Some laminae prepared in the same manner, then washed and dissolved in 

 chlorhydric acid, gave, like the nickel, traces of ammonia. 



t Comptes Rendus, vol. lxxvi. p. 562. 



j We have since ascertained that iron wire, hardening slightly by steep- 

 ing, dissolves at a red heat nearly one fourth of its volume of hydrogen ; 

 the same wire, after cementation, dissolved one third of its volume of the 

 gas. The solubility of hydrogen in steel increases, therefore, with the 

 amount of carbon contained in the latter. 



§ Dingl. Polytech. Journ. vol. clxiii. p. 283. 



|| Arch. Pharm. 2nd Series, vol. cv. p. 284. 



^[ Comptes Rendus, vol. lxxx. p. 319. 



