v THE STUDY OF GASES 65 



between one inflammable gas and another, or between one 

 poisonous gas and another. 



Gases collected over water by Mayow (1674), A few 

 years later, about 1674, the familiar method of collecting 

 gases over water was described by John Mayow, who used 

 it both for investigating the reduction in volume of air 

 during burning and breathing, and for examining gases 

 prepared artificially. 1 For the latter purpose Mayow used a 

 flask inverted in a trough filled with diluted oil of vitriol 

 (Fig. 14, p. 33). The gas was produced by the action of 

 the acid on two or three iron spheres in the neck of the 

 flask. When nitric acid was used, much of the gas dissolved 

 in the liquid, and repeated action of the acid on the metal 

 was needed to fill the flask with gas. With oil of vitriol no 

 such contraction occurred. Mayow proved that these gases 

 possessed the same elastic properties as air, 2 and that, when 

 added to a limited volume of ordinary air, they did not in 

 any degree prolong the life of a mouse confined in it ; but 

 no other tests were made, and Mayow could not be certain 

 "whether air of this kind is really common air or not" 

 (A. C. R. XVII. 113). 



Cavendish prepares "Factitious Air" (1766), Nearly 

 one hundred years intervened between the experiments of 

 Mayow and the appearance in the Philosophical Transac- 

 tions of the Royal Society for 1766 of a remarkable series 

 of three papers by the Honourable Henry Cavendish 

 (1731-1810) entitled "Experiments on Factitious Air." 

 Black had already investigated the part played by " fixed 

 air " in the burning of chalk to lime, and in other related 

 processes. But although he showed that fixed air was 

 present in the atmosphere, he did not attempt to collect or 



1 As described by Boyle in 1660 (Works^ 1725, II. 432). 



- Boyle's tract " Touching the Spring of Air and its Effects" (1660) 

 had recently appeared, so that this point was of special interest at 

 the time (see Chapter XV. p. 320). 



F 



