16 



GRAHAM LUSK 



cover the composition of water. A discussion of the Water Controversy 

 is given by Thorpe. 



Daniel Rutherford (1749-1819) was a pupil of Black's and the uncle 

 of Sir Walter Scott. Rutherford in 1772 described "a residual air," or 

 nitrogen gas, as it is now called. He found that wh^p a candle burned 

 in an inclosed place until it went out and the "fixed air" was then ab- 

 sorbed by alkali, there remained a large volume of air which extinguished 



life and flame in an instant. 

 Priestley (1733-1804) in 

 1771, a year before Ruther- 

 ford's discovery of nitrogen, 

 introduced a growing sprig of 

 mint into an atmosphere in 

 which a candle had burned out 

 and after a lapse of several days 

 found that another candle 

 burned in it perfectly. Evi- 

 dently the burning candle filled 

 the space with phlogiston; the 

 growing plant absorbed the phlo- 

 giston and produced "dephlo- 

 gisticated air." This could again 

 receive phlogiston when the 

 second candle burned. 



Shortly after this discovery 

 (1774) Priestley submitted red 

 oxid of mercury to the heat of 

 a burning glass and found that 

 an air was evolved in which a 

 candle burned very vigorously. 

 Priestley assumed that this air was pure dephlogisticated air, while com- 

 mon air was only partly dephlogisticated. 



And Priestley writes, "My reader will not wonder that, after having 

 ascertained the superior goodness of dephlogisticated air by mice living 

 in it and the other tests above mentioned, I should have the curiosity to 

 taste it myself. I have gratified that curiosity by breathing it, drawing 

 it through a glass siphon, and by this means I reduced a large jar full 

 of it to the standard of common air. The feeling of it to my lungs was 

 not sensibly different from that of common air; but I fancied that my 

 breath felt peculiarly light and easy for some time afterward. Who 

 can tell but that in time this pure air may become a fashionable article 

 in luxury? Hitherto only two mice and myself have had the privilege 

 of breathing it." 



Priestley explained the presence of Black's "fixed air" in the ex- 



Fig. 2. Priestley. From an engraving of 

 a portrait by Gilbert Stuart. 



