Page:Proceedings of the Royal Society of London Vol 1.djvu/405

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Mr. Davy, havingin his last communication to the Society expressed his belief that the substance called oxymuriatic acid gas has not yet been decompounded, but is simple, as far as our, present knowledge extends, and having been conﬁrmed in that opinion by subsequent experiments, endeavours, on the present occasion, to select such experiments as tend to illustrate more fully the nature, properties, and combinations of this substance with inﬂammable bodies, and compares its properties with those of oxygen, to which he considers it as bearing the closest analogy.

When potassium is exposed to oxymuriatic gas, the intensity of their mutual attraction occasions spontaneous inﬂammation. Ten grains of potassium absorb. about eleven inches of the gas; and they form a neutral compound, which is the same as muriate of potash which has been ignited. When this metal or sodium are burned in oxygen gas, the combustion is much less vivid, since their attractions for oxygen are feebler than for oxymuriatic gas; and the alkalies, potash, and soda, are formed in a state of extreme dryness; but under certain circumstances they are liable to combine with an excess of oxygen, and to become peroxides, as observed by Messrs. Gay-Lussac and Thenard.

The oxides, when newly formed, being perfectly dry, require a strong red heat to fuse them. When small quantities of water are added to them, they heat violently, and are converted into hydrates that are easily fused, and are in a certain degree volatile.

By ignition they do not lose the whole of the water. but retain a portion, as has been observed by M. Berthollet and M. D’Arcet. Mr. Davy’ 5 method of ascertaining the quantity of water retained, was by means of the boracic acid, previously dried by heating to whiteness for nearly an hour; and he found about 16 per cent. in potash, and about 23 in soda. But when potassium, or potash re- cently prepared from potassium, was employed, and combined with dry boracic acid, no moisture whatever was extracted. It is evident, therefore, that common potash and soda are hydrates, and that the compounds formed by the combustion of the alkaline metals are pure metallic oxides, free from water.

If one grain of potassium be burned in oxygen gas it absorbs half a cubical inch, and if the oxide so formed be subsequently cxposed to oxymuriatic gas, then one and one eighth cubic inch of this gas are absorbed, and the half cubic inch of oxygen is extricated. When dry potash, or peroxide of potassium, are heated in oxymuriatic gas, no moisture is extricated, excepting when the gas itself contains aqueous vapour. But when muriatic acid gas was introduced