358 Dr. C. Henry's Experiments on the Action of Metals 



ness, the powder became incandescent and was converted into 

 an oxide. A stream of hydrogen directed upon it in this state 

 supported the incandescence for an unlimited period, without 

 the aid of external heat. 



2. Protoxide of cobalt was reduced in a tube by hydrogen 

 at a low red heat, without exhibiting incandescence. During 

 reduction the colour of the powder changed from black to 

 ash-grey. Small portions of the reduced metal, when scat- 

 tered on paper, ignited spontaneously, as in the experiment 

 of Magnus, and inflamed the paper. The rest of the powder 

 was quickly transferred from the reducing tube to a platina 

 dish, upon which a current of hydrogen had been previously 

 directed. The metal instantly became incandescent, and con- 

 tinued to glow as long as hydrogen gas issued in sufficient 

 abundance. No external heat was employed. The substance 

 left at the conclusion of the experiment was in all respects 

 analogous to the original protoxide, except that its colour was 

 of a deeper black. 



Cobalt, then, like the less oxidizable metals, is destitute of 

 the property of inducing the union of hydrogen with free oxy- 

 gen. Its action is the same as that of copper, except that the 

 incandescence takes place during the stage of oxidation, not 

 during that of reduction. 



§ IV. Nickel, 



1. Nitrate of nickel was heated to redness in a porcelain 

 crucible till nitrous fumes ceased to be disengaged. The ash- 

 gray protoxide thus obtained was reduced in a glass tube 

 by hydrogen. During reduction, the colour changed to a 

 brownish black, but the powder did not become incandescent. 

 The metallic nickel was not pyrophoric, nor did it act upon 

 a jet of hydrogen at the temperature of the atmosphere. 

 When slowly heated on a platina tray, the hydrogen con- 

 tinuing to flow over its surface, it became incandescent, and was 

 maintained in that state till the current of hydrogen ceased. 

 The portion of powder contiguous to the orifice from which 

 the hydrogen issued, was distinguished from the remoter parts 

 by a marked difference of colour. That upon which the 

 hydrogen was acting, was of lighter colour than the original 

 protoxide. The powder most distant from the jet was of 

 darker gray, and when heated, without contact with hydrogen, 

 glowed tor a moment, and assumed the same tint as the part 

 that had been kept incandescent. 



2. A second portion of the metallic nickel was simply heated 

 out of contact with hydrogen gas : it became incandescent, 

 but speedily ceased to glow, being reconverted into oxide. 



3. Finally, protoxide of nickel was heated in an open dish, 



