Chemical Science. 375 



were then placed before the fire, till the whole apparatus was too 

 hot to be touched with the naked hand. It was then removed from 

 the fire, and when cooled to its original temperature, the mixture 

 occupied, as before, exactly 38 measures. The powder of platina 

 with hydrogen seems, therefore, to be admirably calculated for 

 eudiometrical purposes. Its application is extremely simple and 

 easy, it is speedy in its effect, and no error need be apprehended from 

 the formation of ammonia, even at considerably elevated temperatures. 

 It appears also to be well calculated for ascertaining the purity of 

 simple gases, at least as far as regards admixture of atmospheric air. 

 The oxygen of a very minute portion of common air, mixed with 

 carbonic°acid gas, and a little hydrogen, was immediately absorbed, 

 on passing up one of the little pellets to the mixture. 



5. On the Action of Platina on Mixtures of Oxygen, Hydrogen, and 

 other Gases.— We noticed in our last Number, p. 179, the singular 

 experiments made by M. Dobereiner, on the ignition of platinum by a 

 jet of hydrogen. Several papers have appeared since then, on the 

 same subject, of the matter of which we purpose giving a very con- 

 densed account, in the following lines. 



The preparation of platinum observed by Mr. E. Davy, which 

 ignites in contact with the vapour of alcohol, is well known. M. Do- 

 bereiner*, by precipitating a solution of platina by sulphuretted 

 hydrogen, and exposing the dry precipitate to the air for a few weeks, 

 obtained an oxidized sulphuret, having similar properties, and further 

 ascertained that both these substances enabled the alcohol to attract 

 oxygen gas, producing acetic acid and water at the same time with 

 the phenomena of ignition before referred to. liy further experi- 

 ments, it was ascertained that neither oxygen nor carbonic acid gas 

 was absorbed by these two substances, but that every inflammable 

 gas was; and 100 grains of the protoxide of platinum (Mr. Davy's 

 substance,) absorbed from 15 to 20 c. i. of hydrogen -gas with igni- 

 tion of the substance, and also of the hydrogen, if previously mixed 

 with air or oxygen. The preparation of platinum charged with hy- 

 drogen readily attracts as much oxygen as will combine with the 

 hydrogen it contains, so that air being admitted, the oxygen in- 

 stantly disappears ; and even ammonia is formed, if there be not enough 

 oxygen for the hydrogen in the platina. The platina immediately 

 reduced, loses some of the properties it before possessed, but retains 

 the power of determining the combination of hydrogen gas with oxygen 

 gas, and with the evolution of so much heat, as, if the experiment be 

 made properly, to ignite the platinum. M. Dobereiner immediately 

 concluded that the platina obtained by heating the ammonia-muriate 

 would have the same effect, and found his expectations confirmed by 

 experiment. This experiment was made July 27, 1823. 



M. Dobereiner considers the phenomenon as an electric one, and that 

 # Annates de Chiinie, xxiv. 91 . 



