2.26 Brunner on the Action of Hydrogen on Metallic Solutions. 



Peroxide of lead, even when, gently heated in a current of the 

 gas, was reduced with explosive violence to protoxide of lead. 

 Oxide of bismuth was slowly, but at last completely reduced to 

 the metallic state. 



The result of these experiments showed that the action of the 

 gas was in all cases reducing; in no case could any carbon be 

 detected in the substances formed. And they further show that 

 at a red heat the affinity of metals for carbon is inconsiderable. 

 The author also subjected the above metallic oxides to the 

 action of olefiant gas. When sesquioxide of iron was heated in 

 this gas, at first a formation of water ensued, which gradually 

 became smaller. The decrease in weight, as ascertained by seve- 

 ral successive weighings, never amounted to 30 per cent., which 

 would have been required by a reduction of the sesquioxide to 

 metallic iron. The maximum decrease was about 20 per cent. ; 

 while there was subsequently an increase of weight. Hence 

 something more than reduction had taken place : either some 

 oxygen was left with the iron, or for a portion of the disen- 

 gaged oxygen some carbon had been substituted. That this 

 latter was the case, was proved by subsequently heating the 

 residue in hydrogen, when neither was any water formed nor 

 was there any change in weight. When the black residue was 

 treated with hydrochloric acid it dissolved with effervescence, 

 and at the same time the characteristic odour perceived in the 

 solution of cast iron was observed, while carbon was set free. 

 Hence part of the carbon was combined and part in a state of 

 mixture ; and the amount of the former appeared to be more 

 considerable than the quantity present in cast iron. The author 

 is of opinion that a partial reduction of the sesquioxide first 

 takes place, and that then this lower oxide, losing some further 

 oxygen, takes up carbon at the same time. 



Protosesquioxide of manganese is at first reduced to greenish 

 protoxide, which afterwards increases in weight, doubtless owing 

 to the separation of carbon. Oxide of copper, heated in a cur- 

 rent of gas, is at first reduced to metallic copper ; and when this 

 is complete, a separation of carbon takes place. 



Brunner* has examined the action of hydrogen on the solu- 

 tions of certain metallic salts. When pure hydrogen was passed 

 through moderately strong neutral solution of nitrate of silver it 

 became turbid, and on continuing the action for several hours a 

 slight grey precipitate was formed, which under the microscope 

 was seen to consist of metallic silver. But the quantity was very 

 small, and did not seem to increase even with several weeks' 

 action. 



* Poggendortf's Annalen, May 1864. 



