32 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



Hooke (1665) & Mayow (1674) suggest that air contains 

 an active principle similar to nitre. The air, to which 

 Jean Rey had attributed the gain in weight of lead and tin 

 during calcination, was regarded by Boyle as having little 

 or nothing to do with this change. It was, therefore, left 

 to his contemporaries, Robert Hooke and John Mayow, to 

 follow up the clue which Rey had provided and to demon- 

 strate the part which air plays, not only in the burning of 

 metals, but in other cases of combustion. 



Robert Hooke, in his " Micrographia " (1665), called 

 attention to the close resemblance between the action of 

 nitre, or saltpetre, and of air in various cases of burning. 

 He regarded air as a solvent for the burning substance, and 

 attributed its activity to the presence in it of a substance 

 similar to (or even identical with) melted saltpetre, but in a 

 very attenuated condition. 



The similarity between air and nitre also formed the basis 

 of the theory of combustion put forward by John Mayow 

 in his " Medico-Physical Works " (Alembic Club Reprints, 

 No. XVII.), published in 1674. He showed, as Boyle had 

 done, that air was not needed for the burning of gun- 

 powder, since damp gunpowder would continue to burn 

 when the tube in which it was contained was plunged under 

 water (A. C. R. XVII. 9). There was, therefore, something 

 in the nitre which would take the place of air in enabling 

 charcoal and sulphur to burn. To this common principle, 

 present in air and in nitre, he gave the name SPIRITUS 



NITRCWEREUS Or NITRO-^ERIAL SPIRIT (A. C. R. XVII. l). 



Mayow (1674) proves that air is absorbed during 

 combustion, Hitherto no attempt had been made to 

 collect and examine gases. When substances were dis- 

 tilled the volatile products were condensed in a cold 

 receiver, in which water was sometimes placed, but gases 

 and vapours which were not condensed in this way had 

 always been lost. To Mayow belongs the credit of intro- 



