32 Chloride of Silver, Hydrogen, and Zinc. [1820. 



nascent state. But lately resuming the experiment, with the 

 intention of ascertaining why the nascent state was more favour- 

 able for the combination of the elements than that of develop- 

 ment, I found reason to suppose that the hydrogen was not at 

 all concerned in liberating the chlorine from the silver. 



When zinc is thrown into chloride of silver, diffused through 

 dilute sulphuric or muriatic acid, hydrogen is liberated, and 

 the chloride suffers decomposition. But the same effect takes 

 place if zinc be thrown into chloride of silver, diffused through 

 pure water, so that the hydrogen which escapes in the state of 

 gas, cannot, in its nascent state, have been the decomposing 

 agent. It may, however, be supposed that water is decom- 

 posed even when no acid is present, and that thus hydrogen is 

 still the agent. But I find that zinc decomposes chloride of 

 silver even more rapidly when unembarrassed by water, than 

 when water is present. Thus, if a little fused chloride of 

 silver and a sntall portion of zinc be heated in a glass tube, a 

 violent action takes place ; chloride of zinc is formed and 

 silver liberated, and the heat rises so high as generally to fuse 

 the silver ; or if dry chloride of silver in powder be triturated 

 in a mortar with zinc filings, the two bodies immediately act, 

 and a heat above that of boiling water is produced. 



Zinc is not the only common metal which thus rapidly de- 

 composes chloride of silver, in the dry way. Tin acts even 

 more powerfully when triturated with it ; and copper and iron 

 have both of them affinities for chlorine strong enough to pro- 

 duce the same effect. 



There is therefore no occasion to assume hydrogen as the 

 decomposing agent, when chloride of silver is reduced in con- 

 tact with zinc or iron (iron acts as zinc does in all these ex- 

 periments, though not so powerfully) ; for the metals, by their 

 attraction for chlorine, are sufficiently energetic to produce the 

 effect. Yet, as I had supposed, from general opinion, that 

 hydrogen could, by its attraction for chlorine, separate that 

 element from silver, I endeavoured to ascertain in what cir- 

 cumstances it had the power of doing so. If a stream of 

 hydrogen, rapidly generated from iron or zinc, be sent against 

 moist chloride of silver, in a dark place or by candlelight, it 

 appears to alter it ; but this effect must be due to metals or 

 impurities held in solution, for when purified it has no power 



