Acids, Alkalis, and their Compounds. 191 



cause the combining weight of sulphur is higher than that of car- 

 bon. And were the doctrine of the influence of elective affini- 

 ties, independent of the operation of external forces on chemical 

 attration, established, barytes would be considered as exerting a 

 more powerful attraction than potash to sulphuric acid, from the 

 attraction of barium to sulphur being stronger than that of po- 

 tassium to sulphur. From the test, however, of the strength of 

 attraction to be found in the capacity for saturation, the attraction 

 of potassium must be inferred to be superior to that of barium to 

 sulphur ; and the results of double decomposition of what are 

 called their saline compounds must be ascribed, in conformity to 

 Berthollet's doctrine, to the influence of the force of cohesion, — 

 this force acting more powerfully on the ternary compound of 

 barium, sulphur and oxygen, than on that of potassium, sulphur 

 and oxygen. These views apply to all the other cases of decom- 

 position in sahne combinations. 



Supplement to the preceding Paper. 



Sir H. Davy has stated some experiments in oj)position to the 

 evidence of water being procured from the action of muriatic acid 

 gas on metals*. On these, as far as they refer to the experi- 

 ments which I executed on this subject f, I may take this op- 

 portunity 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 the alkali in the glass. 



In passing it through glass tubes containing iron ignited, (the 

 experiment I had performed) much more v.'ater appeared. " But 

 this he ascribes principally to the combination of hydrogen dis-r 

 engaged from the muriatic acid gas by the iron, with the oxygen 

 of the common air." Any one repeating this experiment 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 has 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 (juantity of air 

 which the tube could contain, were it even filled with it, is in- 

 adequate to afford, by its oxygen, any sensible production of 

 water in such an experiment. The circumstances and result of 

 the experiment which I have described at page 2!)7 of the Sth 

 volume of the Transactions of the Royal Society of Edinburgh, 

 in which the air in the tube had been previously expelled by the 

 introduction of the gas, and that described p. 298, in which 



* Fhilosophical Transactions for 1H18, Parti. 



+ Edinburgh I'lnlosopliical Transactions, vol. vlii. page 237. 



the 



