vii THE BURNING OF INFLAMMABLE AIR 115 



with inflammable air, Cavendish repeated his experiments 

 with oxygen in place of air. 1 



" In order to examine the nature of the matter condensed 

 on firing a mixture of dephlogisticated and inflammable air, 

 I took a glass globe, holding 8800 grain measures, furnished 

 with a brass cock and an apparatus for firing air by electricity. 

 This globe was well exhausted by an air-pump, and then 

 filled with a mixture of inflammable and dephlogisticated 

 air, by shutting the cock, fastening a bent glass tube to its 

 mouth, and letting up the end of it into a glass jar inverted 

 into water, and containing a mixture of 19500 grain measures 

 of dephlogisticated air, and 37000 of inflammable ; so that, 

 upon opening the cock, some of this mixed air rushed 

 through the bent tube, and filled the globe. 2 The cock was 

 then shut, and the included air fired by electricity, by which 

 means almost all of it lost its elasticity. The cock was then 

 again opened, so as to let in more of the same air, to supply 

 the place of that destroyed by the explosion, which was 

 again fired, and the operation continued till almost the 

 whole of the mixture was let into the globe and exploded.; 

 By this means, though the globe held not more than the 

 sixth part of the mixture, almost the whole of it was exploded 

 therein, without any fresh exhaustion of the globe " (A. C. R. 

 III. 1516). 



The gas remaining in the globe was found to be 2,950 

 grain measures, of which about 1,000 consisted of unburnt 

 oxygen. The residue, which was usually not more than one- 

 fiftieth of the original mixture, Cavendish attributed to impuri- 

 ties in the gases used, and concluded that if these " could be 

 obtained perfectly pure the whole would be condensed." 



The liquid condensed in the globe weighed thirty grains. 



1 Cavendish does not give any illustration of his apparatus ; it was 

 evidently very similar to that of Monge (Fig. 26), but differed in that 

 the gases were not drawn from separate reservoirs but from an inverted 

 jar containing an explosive mixture of the two gases. 



2 " In order to prevent any water from getting into this tube, while 

 dipped under water to let it up into the glass jar, a bit of wax was 

 stuck upon the end of it, which was rubbed off when raised above the 

 surface of the water." 



I 2 



