THE DISCOVERY OF OXYGEN 



surface of the mercury contained in it. At the end of 

 twelve days, when further heating did not cause the forma- 

 tion of any more of the red scale, the retort was allowed to 

 cool. The mercury rose in the bell-jar and the total volume 

 of air was found to have been reduced to 42 or 43 cubic 

 inches, a loss of 7 or 8 cubic inches. The calx on the 

 mercury was collected and found to weigh 45 grains. 

 " The air which remained after this operation, and which had 

 been reduced to five-sixths of its volume by the calcination 

 of the mercury, was no longer fit for respiration nor 

 combustion ; since animals introduced into it perished in a 

 few moments, and lights were extinguished in it at once, 

 as if they had been plunged into water " (loc. at. p. 37). 



As the mercury calx (unlike the black calx from the tin) 

 could be decom- 

 posed by heating 

 it, Lavoisier trans- 

 ferre d the 4 5 

 grains to a small 

 retort and ob- 

 tained from its de- 

 composition 41^ 

 grains of mercury, 

 and 7 to 8 cubic 

 inches of gas, 

 which was " much 

 more fit than 

 atmospheric air to support respiration and combustion," 

 since " a candle plunged into it, gave out a dazzling 

 light; charcoal, instead of burning quietly as in ordinary 

 air, burnt with a flame .... and a brightness of light 

 which the eye could scarcely bear" (loc. cit. pp. 37-38). 



From these experiments it was clear that the whole of 

 the 7 or 8 cubic inches of air absorbed in the first experi- 

 ment had been liberated in an intensely active form in 



FIG. 16 LAVOISIER'S APPARATUS FOR HEATING 

 MERCURY IN A LIMITED VOLUME OF AIR. 

 No illustration is given of the retort used 

 afterwards to decompose the calx. 



