President's Address. 17 



should say, of all combustible bodies. The air, however, 

 could not effect this action until the sulphurous or combus- 

 tible substance was sufficiently heated; and he further ex- 

 plained that the dissolving operation produces great heat. 

 He also taught that this peculiar dissolving action is caused 

 by a substance belonging to or mixed with the air, which is 

 like, if it is not the very same as, that which is fixed in nitre, 

 and that, while the dissolving parts of the air are but few, 

 saltpetre, when red hot and melted, abounds with them. All 

 this, of course, seems to us nothing more than very crudely 

 stated truisms. When we reflect, however, that this theory 

 was propounded more than a hundred years before the dis- 

 covery of oxygen, and when phlogiston was just beginning to 

 be heard of, we cannot but admire the genius of the author, 

 the great success of his experimental research, and the 

 wonderfully correct conclusions he deduced therefrom. By 

 stating that air was the universal dissolvent of sulphurous 

 bodies, he simply meant to say that combustibles exposed to 

 the air, under certain conditions, were dissolved by it. We 

 say, for example, that a piece of charcoal in a red hot condi- 

 tion, exposed to the air, disappears and becomes converted 

 into carbonic acid; while Hooke, writing more than two 

 centuries ago, says that it is dissolved by the air — a state- 

 ment which, it must be admitted, is wonderfully correct. 

 Again, he says that the air will not dissolve the body until 

 that has been sufficiently heated, w^hich is just what we ex- 

 press by saying that different substances ignite at different 

 temperatures ; and further, he tells us that fire is the result 

 of this action, or this dissolving process. More wonderful 

 still, he tells us most distinctly that this dissolving power 

 of the air is owing to a substance inherent in itself, which 

 is like, if it is not the same as, that which is fixed in 

 common saltpetre. We know now, after Priestley's famous 

 discovery has been made, that Hooke, writing more than a 

 hundred years before the result of that was known, was in 

 these statements quite correct. The oxygen, which is the 

 principal constituent of saltpetre, is the same element as that 

 which confers upon air its " dissolvent power." On another 

 occasion Hooke makes the remark, that it is reasonable to 



VOL. V. B 



