President's Address. 29 



which at once set chemical science on a true basis, and made 

 his own name immortal. One of Lavoisier's earliest experi- 

 ments was connected with a subject in which. Scheele also 

 made some investigations. The question which had been 

 pretty keenly discussed for some time, viz., whether water on 

 being heated was converted into earth, was set at rest by the 

 result of this first important experiment. In carrying out 

 this experiment he enclosed a certain amount of water in a 

 glass vessel, and subjected it to heat for 101 days. At the 

 end of that time he weighed the vessel and its contents, but 

 could detect no change in weight. He then opened the 

 vessel, poured out the water and evaporated it, and found that 

 with a slight discrepancy, which he ascribed to experimental 

 error, the water left no solid residue beyond that which it had 

 taken from the glass, and therefore he concluded that water on 

 being heated is not converted into earth. One of Lavoisier's 

 most noteworthy contributions to science was his enunciation 

 of the fact of the indestructibility of matter. He clearly 

 showed that when a chemical change takes place, of whatever 

 nature it may be, there is never any loss of matter. Matter 

 may change its condition, or it may be transferred from one 

 state of combination to another, but still in every case the 

 weight of the sum of the ingredients remains exactly the same. 

 In the year 1772, that is before he had attained his 

 thirtieth year, Lavoisier commenced his famous investiga- 

 tion on combustion, which was destined to yield results 

 of the greatest value to chemical science. As I have 

 already stated, it was the prevailing opinion previous to 

 Lavoisier's time that when such things as phosphorus and 

 sulphur are burned, they are decomposed, and that some 

 mysterious, undefined, and undefinable substance which was 

 called phlogiston was supposed to escape. Lavoisier, how- 

 ever, clearly demonstrated that when such things as these 

 are burned, instead of losing they increase in weight ; and he 

 further showed that this increase arose from their having 

 absorbed and fixed something from without, which something 

 he explained was air ; and he concluded that this absorption 

 takes place when other substances besides sulphur and phos- 

 phorus increase in weight during the process of combustion. 



