23,6 The Rise of the Modern [lect. 



Haller published the first volume of his Elementa, had redis- 

 covered the gas sylvestre of van Helmont, and to a certain 

 extent learned its nature. He recognised it as a distinct gas, 

 as something which, though it might be present in atmospberic 

 air, was distinct from air, was not a mere modification of air. 

 He saw ithat it was irrespirable ; and though he did not lay hold 

 of its nature with sufficient distinctness to justify his calling it 

 by the name applied to it much later and now used by us, the 

 name of carbonic acid gas, he proved by experiment that it arose 

 from burning charcoal. 



Black recognized this fixed air as being present in ordinary 

 air, but he nowhere states to what extent it is so present. It 

 was as we have seen recognized by Mayow, by Haller, and 

 indeed generally that part only of the atmosphere was useful 

 for respiration. Mayow as we have also seen recognized this 

 respirable part as distinct from the rest of the atmosphere ; the 

 others were not so clear, but in any case in Jhe course of the 

 century the words respirable air came into use. Black seems, 

 and that very naturally, to have thought at first that the part 

 of the atmosphere which was not respirable was his ' fixed air ' ; 

 but he was led by a countryman of his to .see that part of the 

 atmosphere though not respirable was something quite different 

 from his fixed air. He says in his Treatise on Chemistry : 



" This portion of our atmosphere (the irrespirable portion, 

 " that which the Swedish chemist, Scheele had called foul air), 

 "was first discovered in 1772 by my colleague Dr Rutherford 

 " and published by him in his inaugural dissertation. He had 

 "then discovered that we were mistaken in supposing that all 

 "noxious air was the fixed air which I had discovered. He 

 "says that after this has been removed by caustic alkali or 

 "lime, a very large proportion of the air remains which ex- 

 " tinguishes life and flame in an instant." 



We may therefore say that nitrogen was discovered by 

 Rutherford in 1772 ; but he did not give it this name, nor was 

 he aware that this irrespirable constituent of the atmosphere 

 had anything to do with the famous nitre which had so much 

 occupied the minds of philosophers of the preceding century. 

 It was not indeed until Cavendish, that eccentric nobleman, 



