Abstract
ALL chemists admit that when sal-ammoniac is volatilised the vapour consists, if not wholly, at least in great part, of hydrochloric acid and ammonia gases in the free state. But this fact, so far as I am aware, is very seldom, if ever, demonstrated experimentally by teachers. The following modification of Pébal's original experiment renders this proof very easy and available for lecture purposes:—
The stem of a long clay tobacco-pipe is passed loosely through a couple of perforated corks fitted into the two extremities of a piece of ordinary combustion tubing about a foot long. The tube contains in the middle a small lump of sal-ammoniac, and near each end a strip of blue litmus paper. When the middle of the tube is heated the vapour of the sal-ammoniac surrounds a portion of the pipe-stem. If, now, a rapid stream of air or any other indifferent gas is sent through the pipe, it is found to be strongly charged with ammonia, so that it answers freely to all the usual tests. At the same time the litmus papers contained in the glass tube become red owing to the accumulation of hydrochloric acid in the residue. This experiment, of course, depends upon the diffusion of the lighter ammonia through the clay more rapidly than the hydrochloric acid also present.
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TILDEN, W. The Dissociation of Sal-Ammoniac—An Experiment. Nature 19, 314 (1879). https://doi.org/10.1038/019314a0
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DOI: https://doi.org/10.1038/019314a0
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