Page:Scientific Memoirs, Vol. 1 (1837).djvu/284

272 , that it is not only chlorine and the analogous bodies which possess decolorizing power; the same property was found in oxygenated water, and the hypermanganates; and at present everything tends to the opinion that oxygenating agents are as effective as chlorine in producing decoloration. Perhaps indeed, as many chemists suppose, chlorine, when acting with water on coloured bodies, produces this effect by indirect oxidation, induced by its tendency to combine with hydrogen.

Welter had, however, made an experiment on this subject which seemed to prove the existence of chlorides of oxides; he found that the decolorizing power of chlorine was constant, whether it was free, dissolved in water, or combined with an oxide.

This remarkable fact could scarcely be explained but by supposing that the chlorine existed in the two cases in analogous conditions. Supposing, therefore, that it was in a state of solution in water saturated with chlorine, it must be admitted that it existed in the state of a chloride of oxide in the decolorizing compound; or, if the latter was a chlorite, it followed that the solution of chlorine in water was a mixture of chlorous and hydrochloric acid; for how can it be supposed that two different bodies, producing decoloration by different causes, can effect it with precisely the same efficacy? The greater number of chemists adopted the first supposition; Berzelius alone preferred the second, although it appeared to be less probable.

The experiments of Soubeiran have since explained these facts. They have shown that Welter's statement was correct only when a solution of sulphate of indigo was used, which, on account of the sulphuric acid it contained, decomposed the decolorizing chloride, and evolved all the chlorine which had served to form it. But if an ink which is not acid or a vegetable infusion be employed as a chlorometric liquor, it is found that the decolorizing power is no longer the same, and that it may always be increased by more than half, by means of an acid which sets free the chlorine contained in the solution of the chlorides.

The property which is possessed by the decolorizing chlorides, of yielding the whole of the chlorine which they contain by the action of the weakest acids, such, for example, as the carbonic acid, has been regarded as a strong proof in favour of their being chlorides of oxides; and it must be admitted that these phænomena of decomposition are much more easily explained by this hypothesis than the other. Nothing is in fact more easily conceivable than the action of an acid combining with a base, and thus disengaging the simple body with which it had formed an ephemeral compound. But this disengagement of chlorine is also easily explained by the hypothesis of chlorites; for it may be conceived that the chlorous acid, set free by the acids themselves, determines a double decomposition, by reacting upon the metallic chlorides with which the chlorites are necessarily mixed by the very mode