U On Sir H. Davy's Theory of [July, 



III. It cannot, when perfectly dry, be made to act on, or unite 

 \yith, charcoal. 



IV. In most, if not in all cases of its evolution, a portion of 

 water is formed. 



Each of these will be the subject of separate examination. 



I. Of the conversion of Oxymuriatic Gas into Muriatic skid, by 

 the action of Hydrogen. 

 It is stated in Dr. Thomson's System of Chemistry,* that 

 water is an essential ingredient of muriatic acid ; and that, 

 hitherto, all attempts to procure it in an insulated elastic form 

 have failed. M. Berthollet remarks, that, after having been 

 exposed to a cold equal to 10° of Fahrenheit's scale, the propor- 

 tion of real acid was to the water as 26'6 to 34-9/f This pro- 

 portion, as Dr. T. observes, is probably excessive; but it must be 

 noted that the means employed by Berthollet were not adequate 

 to the condensation of water held in the elastic form by an 

 affinity so powerful as that between the muriatic acid and its 

 water appears to be. Dr. Thomson considers the proportion of 

 25 per cent, given by MM. Gay-Lussac and Thenard, J as being 

 probably near the truth. Mr. Dalton is, however, inclined to 

 believe that muriatic acid gas contains no aqueous vapour ; and 

 the reasoning employed by him is to the following effect. § If 

 oxygen, hvdrogen, nitrogen, or any of the other gases which are 

 not readily, and in considerable quantity, absorbed by water, be 

 brought into contact with that fluid, the vaporific force of the 

 heat to which they may be exposed will raise a portion of it into 

 the interstices of their particles ; but if fluoric, muriatic, sul- 

 phuric, or nitric acid, in the state of gas, be placed in similar 

 circumstances, an attraction is exerted between it and the 

 water j in consequence of which the acid assumes the liquid 

 form. " Hence," adds Mr. Dalton, " it should seem that 

 these acid gases, so far from obstinately retaining their vapour, 

 lis is commonly imagined, cannot be induced to admit any vapour 

 at all, in ordinary circumstances." This reasoning is very 

 plausible, and certainly highly ingenious ; but it seems to me 

 not unobjectionable. The gas experimented on by Mr. Dalton 

 was of necessity previously saturated with aqueous vapour; and, 

 therefore, could not admit into its constitution an additional 

 quantity. No one would hazard the assertion that muriate of 

 lime contains no water of crystallization, assigning as a reason, 

 that, if a very small portion of water be added to the crystals of 

 this salt they assume the liquid form. Yet it appears to mc 



» Vol. v. p. 778. 



+ Troisitmc Suite dcs rtecherches sur les I.nis de TAffinit^, p. 103, &c. 



X Recherches Physico-Chimiques, tome ii. p. 119, 123. 



t, Now System of" Chemical Philosophy, p. 282. 



