LAVOISIEE. 309 



Dr. Priestley's communication, or the still more repre- 

 hensible statement in his * Elements,' suppressing the 

 hesitating confession of Priestley's priority. With re- 

 spect to Scheele the case is wholly different. What 

 Priestley had discovered in 1774, he discovered the 

 year following, without being aware that he had been 

 anticipated. His process, too, was wholly different 

 from Priestley's, whereas Lavoisier's was the very same. 

 Of these great men, then, Priestley made the discovery 

 in 1774, Scheele in 1775, Lavoisier neither in 1774 nor 

 in 1775, nor ever except by receiving the information 

 from " the true and first discoverer thereof, which, at 

 the time, others did not use."* 



There can be no doubt whatever that it was the dis- 

 covery of oxygen gas which suggested to M. Lavoisier 

 his theory of combustion. He had previously made 

 the important step of explaining the calcination of 

 metals, so far, at least, as showing that it was the 

 union of the metals with the air absorbed, though he 

 was wholly mistaken as to the air which they gave out 

 on reduction, and had a most imperfect notion of the 

 change which their calcination produced on the air in 

 which the process took place ; but now he was enabled, 

 by Dr. Priestley's discovery, to show that the air ab- 

 sorbed i& oxygen gas ; while Dr. Black's great doctrine 

 of heat, which he also called to his assistance, enabled 

 him to perceive that the gas, on becoming fixed, parted 

 with its latent heat, and assumed a solid form. A 

 felicitous idea of Macquer's, which M. Lavoisier cites. 

 ('Mem.,' 1777, p. 572,) that calcination is only a slow 

 combustion, may have given rise to his theory of this 

 operation; but he had also, in his experiments on 

 phosphorus and sulphur, shown the absorption of oxy- 

 gen by those bodies in burning ; and as the doctrine 

 of Dr. Black showed how much heat was evolved on 

 a gaseous body becoming fixed and solid, we may 



* Words of our Patent Act, 21 James I. 



