148 AIR AND LIFE. 



And now, what are the constituents of this mixture? Our knowl- 

 edge of these elements, as well as that of air itself, considered as a 

 whole, is of recent date. While it would require more space than we 

 can spare to give a full historical account of the chemistry of air, the 

 principal facts may be briefly summarized. 



As has been previously stated, a French physician, Jean Rey, was 

 the first who proved the materiality of air, and his experiment was 

 repeated and confirmed by Galileo in 1640, and by Otto von Guericke 

 in 1G50. Jean Mayow, in 1669, was the first to prove that air is not an 

 element, a homogeneous substance. He suspected the fact that air 

 contains two different gases, of which the one, which he called "nitro- 

 aerial/' maintains combustion or fire and respiration, while the other 

 does nothing of the sort. In short, he suspected the presence of the 

 two different gases which are now named oxygen and nitrogen. Had 

 he lived longer, Mayow might have discovered the facts which are the 

 basis of Lavoisier's fame. 



In 1774 Priestly 1 made a great step in the right direction when he 

 succeeded in obtaining the separation of the two principal gases which 

 make up air, and on the same date Scheele 3 did the same, going some- 

 what further, as he discovered the ratio of what he called "dephlo- 

 gisticated air" (or oxygen) to "phlogisticated air" (or nitrogen). Both, 

 however, fell into the same error. Both considered the two gases as 

 identical, but possessing different properties. ISTo doubt the properties 

 are different, but the differences are inherent to the gases themselves; 

 the one is not a form of the other and can not be transformed into the 

 other, and the differences are much more numerous than these two 

 pioneers of chemistry perceived. 



To Lavoisier was reserved the honor of providing precise and unas- 

 sailable knowledge concerning the nature and composition of air. To 

 prove that air, as already demonstrated, is made up of two elements, 

 the one adequate the other inadequate to maintain combustion and 

 respiration, was no difficult task. But he went farther on his road by 

 means of the following experiment, one that is fundamental in the 

 history of chemistry: He placed a known amount of mercury, carefully 

 weighed, in a retort whose long curved neck opened into an inverted 

 glass tube placed on a mercury trough. By means of a curved pipette 

 he sucked out part of the air in the tube, and consequently the mercury 

 rose within it to some height. The point to which the mercury rose 

 was carefully marked, and then the retort was submitted to the influ- 

 ence of heat. The temperature was 360° C, and on the second day 

 he perceived that small red pellicles were forming at the surface of the 

 mercury. During a week, the heating being continued, the pellicles 

 kept forming, and then no more appeared. He kept up his fire during 

 four days more and then put it out. When the apparatus was cooled 



iBoru iu England in 1733; died in Pennsylvania, 1804. 

 2 Born in Sweden in 1742; died 1786. 



