1819.] Acids, Alkalies, and their Compounds. 351 



established that it can be held as demonstrated. The theoretical 

 result no doubt is that hydrogen will be evolved equal to half the 

 volume of the muriatic acid gas, since the latter is formed from 

 equal volumes of hydrogen and chlorine. But circumstances 

 may occur connected with the experiment which will modify 

 this. There is one obvious circumstance of this nature, that of 

 the absorption of a portion of the muriatic acid gas by the 

 muriate formed, whence, as the entire quantity of acid is not 

 decomposed, the quantity of hydrogen produced must, if the 

 experiment be accurately performed, appear less than half the 

 volume. On this point accordingly there has been considerable 

 diversity of result. Sir H. Davy himself, at a former period, in 

 experiments conducted with much care, and having no reference 

 to theory, found that the quantity of hydrogen evolved from the 

 action of potassium and of mercury on muriatic acid gas is 

 equal only to about one-third of the original volume of the gas* 

 "When, therefore, the conclusion is adopted as the ground of 

 argument that the quantity is one-half without any allusion to 

 any difficulty in the experiment, any source of fallacy attending 

 it, or any opposite result having been obtained, its inaccuracy, or 

 at least its uncertainty, may be fairly presumed. I had already 

 observed, in relation to this point, that if the whole water essen- 

 tial to the acid is decomposed by the action of the metal, half 

 the volume of hydrogen ought to be obtained, muriatic acid gas 

 being composed of equal volumes of oxymuriatic gas and 

 hydrogen gas; while, on the other hand, if any additional portion 

 of acid enter into union, besides that forming a neutral compound, 

 the water of this will be liberated, and of course the full propor- 

 tion of hydrogen will not be obtained. I, therefore, endeavoured 

 to determine whether this is the case or not. And in repeated 

 experiments, in which iron and zinc acted on muriatic acid gas, 

 the quantity of hydrogen was always less than the half; and on 

 an average, about 12 measures were obtained when 30 measures 

 had been consumed.* It appears, therefore, that in experiments 

 attended with the results I had obtained ; that is, when a por- 

 tion of water is obtained from the action of metals on muriatic 

 acid gas, and a supermuriate is formed, the quantity of hydrogen 

 evolved is not equal to half the volume of the gas consumed ; 

 and hence, in reference to these experiments at least, Sir H. 

 Davy's attempt to decompose chlorine was very unnecessary, 

 and the want of success, which it was easy to anticipate, affords 

 no argument whatever. 



Muriate of ammonia, it is stated, is not altered by being pass- 

 ed through porcelain or glass tubes heated to redness ; but if 

 metals be present, it affords similar results to muriatic acid gas ; 

 and the water obtained is ascribed to the action of the hydrogen 

 liberated from the acid and from the ammonia, on the action of 



• Philosophical Transactions, 1809, 1810. 



+ Transactions of the Royal Society of Edinburgh, vol. viii. p. 307. 



