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270 deprived of its hurtful properties, while it retained only those which are useful, were soon generally employed in the art of bleaching. They were at first prepared with the solution, and as the first trials were made in the manufactoiy of Javelle, the new liquid with which industry was enriched was called eau de Javelle. But in 1798, Tennant and Knox of Glasgow attempted to substitute hydrate of lime, which forms a solid bleaching compound, while chlorine retains its power only when diluted with a large quantity of water. This substitution was generally adopted, and the new compound, which is more easily preserved and prepared, and at a less price, and more easy of transport, soon became an article of manufacture and considerable commerce, under the name of bleaching powder.

The employment of these compounds of chlorine was further extended in 1822. M. Labarraque, an apothecary of Paris, proved at this period, by numerous trials, that these compounds, which had rendered so many services to the art of bleaching, might be as successfully used for disinfecting. His own trials, and the fresh proofs that his example incited, placed the decolorizing compound of chlorine decidedly among the most valuable resources of the art of preserving health.

We should be at first inclined to believe that the nature of these compounds, which had rendered us such various services, was perfectly understood by chemists; but it is not at all so; and notwithstanding the researches which they have occasioned, the place which they ought to occupy in a classification is not clearly determined. It is, indeed, true that their elementary composition and immediate analysis are well known. In fact, obtained by the action of chlorine upon a metallic oxide, they evidently must be formed merely of chlorine, oxygen, and a metal; on the other hand, the experiments of several chemists have proved that in these compounds, for every two atoms of chlorine, there is one atom each of oxygen and metal. But how are these three elements arranged? This is not at present known with certainty; and yet this knowledge is indispensable for determining by what reactions they serve in decolorizing and disinfecting.

The opinions of chemists on this subject are divisible into two hypotheses. According to some, these compounds are merely chlorides of oxides; according to others, they are to be considered as mixtures of metallic chlorides with a salt which contains an acid of chlorine, less oxygenated than the chloric, and which it has been proposed to call chlorous acid.