. Annals of Philosophy. 440 A Comparison of the Old and New Theories [June, deprived of water, difficultly soluble, and after ignition completely insoluble. In this case a new combustion takes place between the oxygen and chromium already combined ; that is to say, a new electro-chemical discharge, by which the elements not only com- bine more intimately, but the oxygen has lost its former properties, or its former electro-chemical polarization has been exchanged for a complete electro-chemical indifference.* It is clear that if the oxide of chromium at this temperature were gaseous, the produ
. Annals of Philosophy. 440 A Comparison of the Old and New Theories [June, deprived of water, difficultly soluble, and after ignition completely insoluble. In this case a new combustion takes place between the oxygen and chromium already combined ; that is to say, a new electro-chemical discharge, by which the elements not only com- bine more intimately, but the oxygen has lost its former properties, or its former electro-chemical polarization has been exchanged for a complete electro-chemical indifference.* It is clear that if the oxide of chromium at this temperature were gaseous, the produc- tion of fire would cause it to explode, without the ingredients undergoing any new combination with another body (perhaps even a separation), and without the oxide of chromium ceasing to be the same compound, and in the same proportions as before. If we could obtain chromic acid free from water, and in a separate state, probably when exposed to a higher temperature it would exhibit the same appearance of fire and separation of oxygen as takes place with euchlorine in the same circumstances. Edmund Davy found that when a neutral solution of platinum was precipitated by hydro-sulphuret of potash, and the precipitate dried in air deprived of oxygen, a black compound of sulphur was obtained, which, when heated out of the contact of air, gave out sulphur, and some sulphureted hydrogen gas, while a combustion similar to that in the formation of the metallic sulpiiurets appeared, and common sulphuret of platinum remained behind. In this case the very same phenomenon is observable as in euchlorine. The platinum combines at a low temperature loosely with a greater pro- portion of sulphur than it can retain in a higher temperature. When tlie compound is heated there is produced fire, because the platinum combines more intimately with a portion of the sulpliur, and another portion which cannot be retained at that temperature is disengaged. I have found that when we heat the oxide of rh
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