1813.] 



Dr. Joseph Friestley. 



to the establishment of the new chemical doctrine. Fie first 

 discovered the great increase of bulk which takes place when 

 electric sparks are passed through ammoniacal gas; a fact which 

 led directiy to the analysis of ammonia by Berthoilet, who merely 

 repeated Priestley's experiments. His curious experiments on 

 the freezing of water, and the unlimited production of azote 

 from it, remain still unexplained ; and probably will not be 

 understood till some person has succeeded in decomposing azote, 

 and ascertaining its constituents. His experiments on the 

 amelioration of atmospherical air by the vegetation of plants, on 

 the oxygen gas given out by them in the sun, and on the respi- 

 ration of animals, are no less curious : but it would be improper 

 to enter in this place on these difficult and still disputed subjects. 



Priestley m.ay be considered in some measure as the pioneer of 

 Lavoisier. This sagacious philosopher availed himself of all the 

 discoveries of the former, repeated and arranged them, and by 

 means of them chieBy, and of the discoveries of Mr. Cavendish, 

 he succeeded in establishing his peculiar opinions. Priestley 

 continued an advocate for the phlogistic theory till the end of his 

 life; and, the year before his death, published a curious paper, 

 in which he summed up all his objections to the Lavoisierian 

 theory. Many of these objections are easily answered; but there 

 are others which it is impossible to explain. Indeed, the subject 

 cannot be considered as fully decided at present. Lavoisier's 

 theory is more elegant and simple than the other ; but all the 

 chemical tacts known even at present are susceptible of an 

 explanation, according to the doctrine of Dr. Priestley. It 

 would scarcely be fair, therefore, to say that his doctrine is 

 refuted. We prefer the Lavoisierian explanation, because it is 

 simpler and easier than the other ; but it may probably be very 

 different from the theory which will ultimately prevail. Indeed, 

 it is easy to foresee the risk that the Lavoisierian theory runs at 

 present, from the new opinions of Davy respecting muriatic and 

 liuoric acids. The discovery of the prodigious effect produced 

 on the qualities of bodies by the presence or absence of electri- 

 city, a substance (if it be a substance) of so subtile a nature as 

 to produce no effect upon the most delicate balance, and the 

 great changes produced by minute additions of powderable 

 matter, alter all our notions of the composition of bodies. If 

 mercury, for example, can be made solid, and reduced to one- 

 third of its specific gravity, by the addition of one 100,000th 

 part of its weight of tlie metal of ammonia (as is the opinion of 

 Berzelius), how can we be certain that the substances which we 

 find in analysing bodies, constitute even the most material part of 

 their composition. A great deal will depend upon the nature of 

 azote, a substance obviously a compound, though nobody hi- 

 therto has been able to (decompose it, I should not^ for my 



