No. X.] APPENDIX. 189 



pleted by a powerful battery, the metal is deposited on the diaphragm. 

 From this experiment it has been conceived that the acid and oxygen are 

 in combination, forming a proximate principle, which in sulphate of 

 copper is called oxysulphion ; and the salt of copper is believed to be an 

 oxysulphion of copper. When this salt is subjected to the voltaic circuit, 

 he believes it to be directly electrolysed, the oxysulphion passing one way 

 and the copper the other. 



4. This experiment is so much at variance with the electro-chemical 

 doctrine of Dr. Faraday and the inference to be drawn from my cinder 

 experiment, that on rewriting my ' Elements of Electro-Metallurgy,' I felt 

 it to be my duty to examine carefully this hypothesis before I adopted or 

 rejected such an important doctrine. For this purpose his experiments 

 were repeated and varied in different ways ; and with alkalies on the nega- 

 tive side I readily and immediately obtained the metal on the diaphragm, 

 but failed when neutral salts were used on the negative side, or when solu- 

 tions of gold and platinum were employed on the positive. A series of 

 experiments were then instituted on the polarity of solid substances inter- 

 posed between two platinum poles. I placed a series of copper wires in all 

 directions and situations between the poles, in a solution of sulphate of 

 copper, and found that one part of each wire became positive and was dis- 

 solved, and another part of the same wire became negative and reduced the 

 metal from the solution ; so that all the wires were, at different parts, either 

 dissolving "or increasing. I next extended my examination as to the capa- 

 bilities of platinum wires to become polar, and found that a much greater 

 resistance was effected in this case than when other metals were employed ; 

 still, however, by particular management they were readily made to give 

 off abundance of gas (' Elements of Electro-Metallurgy,' p. 53, 2nd edit.). 



5. The polarity of interposed conducting substances having been fully 

 proved, I endeavoured to ascertain how far non-conducting bodies would 

 take on a similar condition, but could not obtain very satisfactory proof on 

 this matter. Sufficient evidence not being obtained to prove the possibility 

 of interposed non-conducting substances to become polar, I determined not 

 to rely on the investigation for the cause of the reduction of the metals on 

 these experiments, but seek proofs from other causes. 



6. I repeated the experiments made in 1839, and communicated to the 

 ' Philosophical Magazine ' in 1840, from which I discovered that porous 

 coke or charcoal, when arranged as the negative pole in dilute sulphuric 

 acid, absorbed a large quantity of hydrogen. The mode in which I repeated 

 these experiments was as follows : A piece of well-burnt charcoal or 

 cinder was removed red-hot from the fire and quenched in dilute sulphuric 

 acid, so that all chance of the presence of oxygen in its texture might be 

 precluded. In this state it had no effect on metallic solutions. It was 

 then arranged as the negative pole in dilute sulphuric acid by connecting 

 it with the voltaic battery, when it became charged with hydrogen, which 

 was ascertained by the circuit being completed some time before gas was 

 evolved from its surface. Pieces of coke thus charged with hydrogen 

 were dipped into various metallic solutions, when the metal was instantly 

 deposited as a brilliant coating on the coke. The deposit of copper 

 affords the most beautiful example, though the deposit of other metals, 

 as of silver and gold, is also striking. Coke charged with hydrogen retains 

 the property of reducing metals many days after its first saturation. 



