CHEMISTRY OF THE EIGHTEENTH CENTURY. 365 



very near its boiling-point. Nothing remarkable took place during 

 the first day: the quicksilver, though not boiling, was continually 

 evaporating, and collected in the upper part of the retort in small 

 drops, which from time to time passed down again to the bulk of 

 the quicksilver at the bottom of the vessel. On the second day 

 small red particles began to appear on the surface of the liquid, and 

 during the next four or five days the quantity of these gradually 

 increased ; but after that 

 time no further change 

 was observed, although 

 the experiment was pro- 

 longed for twelve days, 

 The fire was then extin- 

 guished, and the appara- 

 tus allowed to cool. The 

 capacity of the retort, 

 including its neck, and 

 that of the bell jar, having 

 been determined before 



the beginning of the ex- . FlG I?4 



periment, Lavoisier knew 

 what volume of air filled the parts of the vessel not occupied by the 

 quicksilver at the beginning and at the end of the experiment. He 

 found that at the end one-sixth of the air had disappeared, and that 

 the residual air was no longer fit either for respiration or for combustion. 

 Animals put in it were suffocated in a few seconds, and a taper plunged 

 into it was extinguished as quickly and completely as if it had been 

 put into water. 



The red matter which had formed on the mercury in the experi- 

 ment just described was collected by Lavoisier, and put into a small 

 glass retort, which was connected with a proper apparatus for receiving 

 such liquid or gaseous products as might be given off when a strong 

 heat was applied. The result of heating the red substance was that 

 it gradually decreased in bulk, and soon altogether disappeared ; and 

 When 45 grains of it were so heated, the receiver was found to contain 

 41^ grains of liquid mercury, and into a bell jar 7 or 8 cubic inches 

 of a gas had passed. This gas was found capable of supporting respi- 

 ration and combustion more vigorously than common air. Lavoisier 

 remarks that this species of air was discovered at nearly the same time 

 by Priestley, Scheele, and himself; and, indeed, there is little doubt 

 that at about the same period these three chemists did, independently 

 of each other, discover oxygen. Priestley, as we have seen, called it 

 " dephlogisticated air; " Scheele called it empyreal air; and Lavoisier 

 at first named it air eminently fitted for respiration, but afterwards substi- 

 tuted the shorter term vital air, and finally gave it, for reasons which 

 will have to be discussed presently, the name it still bears, viz., oxygen. 



