S56 Dr. C. Henry's Experiments on the Action of Metals 



ignited and cooled under mercury, and pounded glass washed 

 in hot alkali and acid and then repeatedly in distilled water, 

 when introduced into curved tubes containing oxygen and 

 hydrogen in the proportions constituting water, did not induce 

 the silent union of the gases, until the tubes were heated to 

 near the boiling-point of mercury. All these substances acted 

 nearly at the same temperature. 



§ I. Copper, 



1. Oxide of copper, obtained by calcination of the nitrate, 

 was exposed in a green glass tube to a current of hydrogen, 

 issuing from dilute sulphuric acid and zinc. The temperature 

 was gradually raised by a spirit-lamp to a low red heat, when 

 the process of reduction commenced, and the bright incan- 

 descence, described by Berzelius, was observed to spread 

 along the powder, in the line of reduction, even after the lamp 

 had been withdrawn. The metallic copper thus obtained 

 was light and spongy, and underwent no change in the atmo- 

 sphere at ordinary temperatures. 



2. A portion of this copper, exposed to the air in an open 

 capsule, was heated on a sand-bath to upwards of 500° 

 Fahrenheit, and a stream of hydrogen made to flow constantly 

 over its surface. The gas was not inflamed, but the metal 

 itself became rapidly tarnished, and was finally reconverted 

 into black oxide. Precisely the same change was effected by 

 simply heating the metal without the presence of hydrogen. 



3. Oxide of copper, thrown down from the sulphate by 

 caustic potassa, and sufficiently washed with distilled water, 

 was reduced in the same manner. A jet of hydrogen was di- 

 rected upon the pure and porous copper so obtained, which 

 was then slowly heated on a platina dish by a spirit-lamp. 

 As in the last experiment, it speedily began to lose the metallic 

 aspect, and was reconverted into black oxide. The heat was 

 increased to near redness, when the powder suddenly be- 

 came incandescent, and though the lamp was withdrawn, con- 

 tinued to glow brightly as long as the current of hydrogen 

 was supplied. In appearance the incandescence was identi- 

 cal with that of powdered platina or rhodium under like cir- 

 cumstances. 



Copper, then, in a state of fine mechanical division, does not, 

 like platina, dii'ectly induce the union of hydrogen with oxy- 

 gen at any temperature. At all temperatures below that at 

 which its oxide is reducible, the affinity of copper for oxygen 

 surpasses the affinity of hydrogen for oxygen. Hence when 

 heated in the open air, either with or without the presence of 

 hydrogen gas, the copper absorbs oxygen, and is finally con- 

 verted into the state of black oxide, hydrogen, it' present, 



