in determining Gaseous Combination, 363 



candescent, and to inflame the gas, if oxygen be present. 

 Mitscherlich also regards the action of charcoal, in causing the 

 rapid union of sulphuretted hydrogen and oxygen, as identi- 

 cal in character with that of platina on other gaseous mix- 

 tures*. Other experimenters have stated, on the contrary, that 

 platina exerts no appreciable action on pure hydrogen or pure 

 oxygen, and have sought the theory of its operation in the 

 phaenomena of its contact with those gases in a state of mix- 

 ture f. It appeared, therefore, important to contrast by fresh 

 observations the action of platina with that of charcoal upon 

 the simple gases. 



In these experiments I employed box- wood charcoal, which 

 was heated to redness and cooled under mercury before ad- 

 mission into the gases. The results constituted a series of 

 numbers very nearly accordant with those of Saussure, with 

 the single exception of sulphuretted hydrogen, which was ab- 

 sorbed in larger proportion than is stated by that experi- 

 menter. One volume of charcoal, I found, absorbed eighty- 

 one volumes of sulphuretted hydrogen. The absorption was 

 always effected with far greater rapidity during the first mo- 

 ments of contact with all the gases than afterwards. 



Platina, in the form of sponge and of clay balls, was simi- 

 larly introduced into tubes containing the separate gases over 

 mercury. No immediate diminution of volume could ever be 

 detected ; and in most trials, the space occupied by the gas 

 was increased by a quantity equivalent to the volume of the 

 platina sponge or ball. In some cases, when the sponge was 

 left for a day or two in contact with the gas, there was an 

 appreciable, though very slight absorption. Thus, a small 

 piece of sponge passed into 5 cubic inches of hydrogen did not 

 by its own bulk augment the volume of the gas, and after the 

 lapse of two days had absorbed about ^ cubic inch. In not 

 one of the many experiments in which platina was introduced 

 into pure oxygen gas, and allowed to remain for several days, 

 was there any appreciable absorption. Even ammoniacal, 

 muriatic acid and sulphuretted hydrogen gases, which are so 

 largely and rapidly condensed by charcoal, underwent no 

 immediate change of volume from exposure to spongy platina, 



* Lehrbuch der Chemie, b. i. p. 226 and 394. 



t Marcet and Delarive, Ann. de Ckim. et de Phys., torn, xxxix.; and Dr. 

 Faraday (5H7). [It is remarkable that this statement had been originally 

 made also by Dobereiner, as appears from a paper by Dr. Schweigger, in 

 the Journal bearing his name, of which a translation was given in Phil. 

 Mag., vol. Ixiv. p. 3. Schweigger quotes Dobereiner as saying that " the 

 hydrogen is neither absorbed nor condensed by the metallic platinum dust, 

 and in the recital of his experiments, that " No condensation of hydrogen 

 occurred when I placed it in contact with platinum dust," and certain 

 other substances which he mentions. — Edit.] 



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