1 6 HISTORY OF CHEMISTRY. [LECTURE II. 



scientific views. Even here, we must not commit ourselves to 

 any blind belief, neither must we regard this law as absolutely 

 exact ; and, however difficult we may find it to build up a 

 scientific edifice without it, still we must never forget that, just 

 like all other laws, it is merely the expression of facts which 

 we have observed; that there are errors connected with all 

 our observations ; and that on this account the possibility is 

 not excluded that succeeding centuries may reject the law 

 itself. 



Meanwhile, however, we must regard this law as the greatest 

 achievement of chemistry, and as one of the firmest supports of 

 all natural science ; while from the period of its general accepta- 

 tion we date the commencement of a new era in chemistry ; 

 that is, of the chemistry of to-day. It will thus be understood 

 why I desire to direct most especial attention to the period at 

 which this law was stated and was put to the test ; and why I 

 enter upon a detailed account of Lavoisier's experiments, from 

 which the accuracy of the principle was deduced. 



Many hold the view that the reorganising effect which our 

 science experienced, is to be attributed to the discovery of 

 oxygen, which fell not altogether fortuitously within the 

 period mentioned. This is not the case, however ; and the 

 history of chemistry itself furnishes proof of the fact, inasmuch 

 as Priestley and Scheele were the discoverers of oxygen, while 

 Lavoisier was the reformer of chemistry. I cannot resist the 

 temptation to point out how the endeavour was made to bolster 

 up phlogiston, and how Priestley and Scheele made every con- 

 ceivable effort to bring the astonishing properties of oxygen 

 into harmony with the existence of phlogiston (which had never 

 yet been demonstrated). 



Priestley discovered oxygen in 1771. He isolated and ex- 

 amined it, and the priority of the discovery is his. He 

 published a detailed account of it in 1 7 7 5- 1 Scheele's investiga- 

 tion appeared two years later, but it has been shown that his 



1 Priestley, Experiments and Observations on different kinds of Air, Vol. 

 2, London (1775), 2 9 > Alembic Club Reprints, No. 7, 5. 



