150 AIR AND LIFE. 



etc., but this is not the place to describe them, and all text-books of 

 chemistry give a full account of tliem. 



It is enough for our purpose to know that it is fully established that 

 atmospheric air is a mixture; that this mixture is principally made up 

 of oxygen and nitrogen, and that we are provided with methods and 

 implements by means of which air may be analyzed, and the least 

 traces of its constituent elements detected. 1 



These elements are numerous, but they differ greatly in importance. 



Fundamentally, air comprises 20.81 volumes of oxygen, 79.19 volumes 

 of nitrogen, and some ten-thousandths of carbon dioxide. In some 

 localities or under certain circumstances a few other 2 gases may also 

 be found in air, in very small quantities. 



We must now consider in turn each of these elements. 



Oxygen comes flrst. JSTot that it is present in the greatest abundance, 

 but from many points of view it is a most important part of the 

 atmosphere. 



This gas is heavier than air as a whole (while nitrogen is lighter), 

 and in 1,000 liters of air there are 208 liters of oxygen against 792 of 

 nitrogen. This ratio seems to be constant, although Dal ton and Babi- 

 net, arguing theoretically, supposed that oxygen is less abundant in 

 the air at high altitudes, and that the proportion of this gas decreases 

 as the distance from the sea level is increased — oxygen being rather 

 more abundant in low regions, and near the surface. Of course, if such 

 were the case, the reverse would obtain for nitrogen. This gas should 

 be more abundant at high levels, and less near the sea level. Accord- 

 ing to the views of Dal ton and Babinet, at 10,000 meters above the sea 

 level, 1,000 liters of air should contain only 184 liters of oxygen against 

 816 of nitrogen. These speculations may be interesting, but as they 



1 In view of recent facts this is too positive a sentence. Great was the surprise of 

 the chemists when they heard that Lord Rayleigh and Professor Ramsay had discov- 

 ered a new element in atmospheric air. This should inspire them with some caution, 

 and induce them not to put so much faith in the infallibility of their methods. 

 More of this hereafter. [Note added to proofs in 1896]. 



s To the normal constituents of atmosphere one remains to he added, and that is 

 argou, discovered in the year 1894 by Lord Rayleigh and Professor Ramsay, to 

 whom, on this account, the $10,000 Thomas Hodgkins prize has been most deservedly 

 awarded. 



Argon, thus called because it seemed to be an inert and inactive gas, slow to 

 combine with other substances, was certainly contained in Cavendish's test tubes, 

 but Cavendish considered it as nitrogen, and thus failed to add this substance to 

 the list of chemical elements. Argon is present in the atmosphere in the proportion 

 of somewhat less than 1 per cent; M. Th. iSchloesing obtains 0.935 argon for 100 

 air, in volumes. MM. MacDonald and Kellar have in vain endeavored to detect 

 argon in the chemical constitution of animals and plants (mice and pease), but Mr. 

 Ramsay has found it in meteoric iron. Argon liquefies at — 128 c under 38 atmos- 

 pheres pressure, and freezes at — 189°. It is not as inactive as at first supposed, 

 as Berthelob has been able to combine it with benzine under the influence of the 

 electric discharge. This gas does not seem to play any active part in respiration ; it 

 is inert and useless, like nitrogen. [Note added to proofs, 1896.] 



