AIR AND LIFE. 149 



down, lie saw that in the glass tube the mercury rose higher than 

 before the experiment, and he observed that the remaining gas was 

 unable to maintain respiration and combustion. In it small animals 

 died and a light went out. He then collected the red pellicles, weighed 

 them, put them in a retort whose neck opened under a glass tube 

 filled with mercury, and heated the retort to 400° C. The pellicles 

 melted away; they yielded a certain amount of mercury which was 

 deposited in the neck of the retort, while in the glass tube some cubic 

 inches of a peculiar gas had accumulated at the top. The volume of 

 this gas corresponded exactly with the volume of air which had dis- 

 appeared in the preceding experiment, and this gas was fully able to 

 maintain combustion. 



Thus was performed the first analysis of air, and Lavoisier came to 

 the conclusion that that fluid contains two gases — one which forms 

 one sixth of the whole volume and is favorable to combustion and 

 respiration, while the other, amounting to five-sixths of the whole 

 volume, is favorable to neither. The first was oxygen ; the last azote, 

 or nitrogen. 1 



It is now more than a century since these facts were discovered, and 

 became the corner stones of modern chemistry. Up to that time it was 

 mere empirical alchemy, and a fabric of erroneous notions. A number 

 of methods, much superior as far as precision is concerned, have been 

 devised for the purpose of air analysis, and of gas analysis generally. 



The eudiometric method, propounded by Gay-Lussac and Humboldt, 

 is one of the best known. It is based upon the fact that if hydro- 

 gen is added to air, and the electric spark passed through the mix- 

 ture, the oxygen of the air and the hydrogen added to the mixture 

 combine in definite and constant ratio and form water. A very simple 

 calculation gives the amount of oxygen contained in the mixture. The 

 weighing method of J. B. Dumas and Boussingault, invented in 1841, 

 is quite different. It is based upon the fact that when air, deprived 

 of aqueous vapor and carbon dioxide, is made to pass through a tube 

 containing metallic copper reduced by means of hydrogen, and heated 

 to redness, it yields its oxygen to the copper, and if the copper is 

 weighed before and after, the amount or weight of oxygen contained iu 

 the volume of air experimented upon is at once known. If the remain- 

 der of the gas, that portion which has not combined with the copper, 

 be collected in an empty receiver weighed before and after the experi- 

 ment, the increase in weight of" the receiver shows the quantity of 

 nitrogen contained in the original volume of air. Twenty other meth- 

 ods, more or less similar to the preceding one, have been devised by 

 Brunner, Begnault and Beiset, Doyere, Bunsen, Williamson, Bussell, 



'These names were given by Lavoisier. Oxygen is derived from 6%vS, acid, and 

 yevvaoo, to produce, because one of the properties of oxygen is to form acids when 

 combined with many otber substances. Azote is derived from privative a and Zooi'?, 

 life, because azote is not suitable for living animals, and can not maintain life. 



