224 SCIENTIFIC AMUSEMENTS. 



Expt. 269. To reproduce Oxide of Copper from Spongy- 

 Copper and vice versa alternately. Carry out the last experi- 

 ment, and when the oxide of copper is almost wholly reduced to 

 spongy metal, detach the hydrogen generator, and substitute for it 

 a tube connected with a gasholder or bladder, &c. (Expt. 177) 

 containing oxygen, so as to send a stream of oxygen gas through 

 the tube instead of hydrogen ; the red spongy copper will now 

 combine with the oxygen and reproduce a black mass of oxide of 

 copper in so doing; by alternately coupling on the stream of 

 hydrogen from the hydrogen generator and the current of oxygen 

 from the gasholder, you can bring about at pleasure the two con- 

 verse actions, reduction of oxide of copper to metal with formation 



Fig. 95. Oxide of Copper reduced by Hydrogen. 



of water, and combination of copper with oxygen to reproduce 

 oxide of copper. 



If the copper be fed with oxygen sufficiently rapidly, it will be 

 seen that the spongy metal becomes red hot and glows during 

 oxidation, a considerable degree of heat being obviously produced, 

 although not as much as when magnesium, zinc, or iron unites 

 with oxygen, as in experiments 231, 232, and 233. 



In the extraction of many of the metals, &c., employed for 

 various useful purposes in the arts from their natural sources, 

 processes are employed on the large scale, the general principle of 

 which is much the same as that involved in the separation of tin, 

 lead, bismuth, and copper from their respective oxides; and of 

 mercury, antimony, &c., from their sulphides, by the processes 



