CHAPTEE II. 



CHEMICAL CONSTITUTION OF THE AIR. 



DIFFICULTIES which appeared quite insur- 

 mountable had long beset the investigations of 

 chemists upon the composition of the air. Long 

 after the revival of experimental chemistry the 

 most erroneous impressions were afloat; and 

 chemists, in their discordant analyses, only in- 

 creased the confusion by the vast discrepancies 

 which occurred between the results of one 

 analyst and those of another. Until the middle 

 of the eighteenth century, the opinion was very 

 prevalent that the atmosphere formed one of 

 the four elementary bodies, that it was, in fact, 

 a simple, undecomposable gas. It was reserved 

 for the talented Dr. Priestley to dispel this 

 error. He discovered the existence of a new 

 gas which formed one of the constituents of air. 

 In this gas it was found that combustion took 

 place with extraordinary intensity ; even iron- 

 wire, heated red-hot and plunged into it, caught 

 fire, and burnt away ! Other combustibles gave 

 out showers of the most brilliant sparks, and 

 produced the most intense heat, when placed in 



