232 EIGHTEENTH CENTURY. FT. in. 



cury ; while the red colour began to disappear in the bulb, 

 #, and only pure shining mercury remained behind. So far 



FIG. 41. 



Priestley's Apparatus for procuring Oxygen. 



a, Bulb containing red mercuric oxide, b, Vessel containing mercury, c, Inverted 

 jar for collecting the gas. d, Burning glass. 



he had only proved that red mercuric oxide is made up of 

 mercury and a gas. 



When he had collected enough gas to experiment upon 

 he passed some of it through water, and found that it did not 

 dissolve as * fixed air ' does ; but what surprised him still 

 more was that a candle put into it burnt with a large 

 vigorous flame, and a piece of red-hot charcoal burnt 

 in it furiously. It was clear, then, that this could not 

 be either 'fixed air' or 'inflammable air,' for neither 

 of these would feed a flame. He next put two mice into 

 some of the gas, and he found that they lived much 

 longer than they would have done in the same amount of 

 ordinary air. When he breathed it also into his own chest 

 he felt singularly light and easy for some time afterwards. 

 ' Who can tell,' he writes, ' whether this pure air may not 

 at last become a fashionable luxury ? As yet only two 

 mice and myself have had the privilege of breathing it.' 



