Page:Experimental researches in chemistry and.djvu/47

32 nascent state. But lately resuming the experiment, with the intention of ascertaining why the nascent state was more favourable for the combination of the elements than that of development, 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 decomposed 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 small 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 decomposes 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 produce the same effect.

There is therefore no occasion to assume hydrogen as the decomposing agent, when chloride of silver is reduced in contact with zinc or iron (iron acts as zinc does in all these experiments, 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 circumstances 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