350 Dr. Murray on the Chemical Constitution of [Nov. 



riments which I executed on this subject,* I may take this 

 opportunity of offering a few observations. 



In passing muriatic acid gas through glass tubes ignited, Sir 

 H. Davy found water to be deposited, which he ascribes to the 

 action of the acid on the oxide of lead and alkali in the glass. 



In passing it through glass tubes containing iron ignited (the 

 experiment I had performed), " much more water appeared ; " 

 but this he ascribes principally to the " combination of hydrogen 

 disengaged from the muriatic acid gas by the iron, with the 

 oxygen of the common air." Any one repeating this experi- 

 ment will at once be satisfied that this circumstance can have 

 little or no effect in producing the result. The water does not 

 appear until the air lias been expelled from the tube by the 

 introduction of the muriatic acid gas ; it continues to increase 

 after this when no air can be supposed present ; and the whole 

 quantity of air which the tube could contain were it even filled 

 with it, is inadequate to afford by its oxygen any sensible produc- 

 tion of water in such an experiment. The circumstances and 

 result of the experiment which I have described, p. 297, of the 

 eighth volume of the Transactions of the Royal Society of Edin- 

 burgh, in which the air in the tube had been previously expelled 

 by the introduction of the gas, and that described, p. 2b'8, in 

 which the air had been withdrawn from the retort by previous 

 exhaustion, altogether preclude this supposition. But its utter 

 inadequacy will, to any one taking the trouble of repeating the 

 experiment, be sufficiently apparent. 



It is stated that in the action of muriatic acid gas on metals, 

 hydrogen, equal in bulk to half the volume of the gas, is pro- 

 duced ; and, therefore, it is added, if water had been generated 

 by the action of muriatic acid gas on metals, it must have been 

 the chlorine, or the metal, or both, that were decomposed. 

 " But in an experiment of passing chlorine gas over ignited 

 metals, not the slightest appearance of moisture was percep- 

 tible." 



This argument, in common with some others of Sir. H. Davy's 

 results, may apply with sufficient force to those experiments in 

 which it is said, that water was obtained equal or nearly so 

 to the whole quantity of water, which, according to the old 

 doctrine, is contained in muriatic acid gas ; for it is evident that 

 this water could not have been deposited, and hydrogen likewise 

 evolved. But it does not apply to my experiments, in which a 

 small though very sensible portion of water was obtained ; for in 

 such a case hydrogen gas will also be produced, though not to 

 the precise amount of half the volume. The actual result, there- 

 fore, in the particular form of experiment employed, ought to be 

 ascertained, instead of a general conclusion being reasoned on, 

 more especially when even the general fact is not so clearly 



* Edinburgh Philosophical Transactions, vol. viii. p. 287. 



