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The Bakerian Lecture. On some of the Combinations of Oxymuriatic 

 Gas and Oxygen, and on the chemical Relations of these Principles, 

 to inflammable Bodies. By Humphry Davy, Esq. LL.D. Sec. R.S. 

 F.R.S.E.M.R.I.A. and M.R.I. Read November 15, 1810. \Phil 

 Trans. 1811, p. 1.] 



Mr. Davy, having in his last communication to the Society ex- 

 pressed 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 se- 

 lect such experiments as tend to illustrate more fully the nature, pro- 

 perties, and combinations of this substance with inflammable bodies, 

 and compares its properties with those of oxygen, to which he con- 

 siders 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's 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 1 6 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 ex- 

 posed 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 oxymu- 

 riatic gas, no moisture is extricated, excepting when the gas itself 

 contains aqueous vapour. But when muriatic acid gas was introduced 

 2 c 



