President's Address. 27 



be produced, he had really no very clear ideas on the subject 

 of water being a chemical compound of hydrogen and oxygen, 

 and that in point of fact his own opinion of the matter was 

 that the water existed ready formed in the hydrogen or in- 

 flammable air as he called it. Cavendish to the last was a 

 firm believer in phlogiston, and it seems to me that his strong 

 faith in that most ridiculous of theories must have tended 

 to warp his mind, and frequently to lead him off the 

 path of truth. Thus he says, speaking of the results of 

 his researches on water : " From what has been said, there 

 seems the utmost reason to think that dephlogisticated air is 

 only water deprived of its phlogiston, and that inflammable 

 air is either phlogisticated water or else pure phlogiston, but 

 in all probability the former," Had his mind not been 

 imbued with this theory of phlogiston, would it not be very 

 natural to suppose that Cavendish, having put two gases 

 together, and after having fired them, finding the gases dis- 

 appear and water produced in their place, would come to the 

 conclusian that the water had been formed from them, and 

 was therefore composed of them. Unfortunately, however, 

 the phlogiston was dragged in, and the obvious and simple 

 explanation of the result of his experiment was ignored. 



We have now reached what must be considered one of the 

 brightest periods in the history of chemical science. Oxygen 

 has been discovered by Priestley, Black has experimented with 

 fixed air, and Cavendish has made his masterly researches on 

 inflammable air. Mtric oxide, hydrochloric acid, ammonia, 

 sulphurous acid, and a number of other gases are known. 



The famous discovery of Cavendish leads us to consider the 

 valuable results which were being obtained at this time by 

 the world-renowned Scheele, then a poor Swedish apothecary. 

 Scheele, like some of the other great chemists of his day, was 

 a firm believer in phlogiston, and, as might be expected, he 

 in consequence, like them, fell into a great many errors in 

 explaining the results of some of his experiments. Scheele, 

 however, will long be honourably remembered as the dis- 

 coverer of chlorine, and also for his valuable researches on 

 Prussian blue, which led, among other things, to the isolation 

 of Prussic acid. Scheele, it should be noticed, also discovered 



