v THE STUDY OF GASES 81 



Effects such as these gave to the gas the popular name of 

 " laughing gas." Its permanent utility as an anaesthetic in 

 dentistry is forshadowed in Davy's own experience : 



"The power of the immediate operation of the gas in 

 removing intense physical pain, I had a very good 

 opportunity of asertaining. 



"In cutting one of the unlucky teeth called dentes 

 sapientiae, I experienced an extensive inflammation of the 

 gum, accompanied with great pain, which equally destroyed 

 the power of repose, and of consistent action. 



" On the day when inflammation was most trouble- 

 some, I breathed three large doses of nitrous oxide. The 

 pain always diminished after the first four or five inspirations ; 

 the thrilling came on as usual, and uneasiness was for a few 

 minutes swallowed up in pleasure. As the former state of 

 mind however returned, the state of organ returned with it ; 

 and I once imagined that the pain was more severe after 

 the experiment than before" (Works, III. 276). 



C ACID AIR AND ALKALINE AIR. 



Cavendish (1766) collects "marine acid air," From 

 the time of Glauber it had been customary to prepare 

 muriatic acid by distilling into water the pungent gas 

 produced by the action of strong oil of vitriol on common 

 salt (Chap. II, p. 14). The gas was first collected by 

 Cavendish in " an experiment with design to see, whether 

 copper produced any inflammable air by solution in spirit of 

 salt." He found that he "could not procure any inflammable 

 air thereby," but, on the application of heat, he was able to 

 drive off a considerable quantity of gas which had the 

 peculiar property of " losing its elasticity when in contact with 

 water." The gas set free in the bottle containing the copper 

 and acid (Fig. 18) was at first separated from the water 

 in the receiver by a "barrier of common air," but as soon 

 as this was removed the dissolution of the gas proceeded 



G 



