22 ARGON CARBON DIOXIDE 



Argon is a gas possessed apparently of no chemical properties 

 whatever ; that is, it appears to be incapable of uniting with any other 

 substance or even with itself, for, unlike most gases, its molecule 

 contains only one atom. Its density, when carefully purified, was 

 found to be 19-94, which gives as its atomic (and molecular) weight 

 the number 39*88. So far as is known, argon takes part in none of 

 the chemical changes which occur in the atmosphere. 



Associated with argon, Eamsay has found several other gases of the 

 same inert character and monatomic molecules, but differing in density 

 and other physical properties. These have been named helium (identi- 

 cal with the substance so named, which was, long ago, detected in the 

 sun by spectroscopic analysis), density 2-0 ; neon, density, 1OO ; 

 krypton, density, 41 '4 ; and xenon, density probably about 65. These 

 elements, however, are present in such extremely small quantities and 

 their chemical inertness is so great that they are probably of no import- 

 ance from our present standpoint. 



The amount of argon present in the air is apparently very constant 

 about 0'94 per cent by volume or 1-3 per cent by weight. It consti- 

 tutes about 1'19 per cent by volume of the residue left after the re- 

 moval of oxygen. 



Carbon Dioxide. This constituent, though present only in small 

 proportion (usually less than -04 per cent by volume), is of great im- 

 portance with reference to vegetable life. Its amount is subject to 

 considerable variation, since it is a constant product, in large quantity, 

 of the combustion and putrefaction of all organic bodies. 



In the free open country, air contains on the average about -033 

 per cent of carbon dioxide. 1 In large towns or in the neighbourhood 

 of manufactories the quantity is usually larger. In London, Angus 

 Smith found '044, in Glasgow '05, in Manchester '045. The amount is 

 always greater during .fogs (sometimes rising to O'l per cent) and snow. 



Air in the country shows a distinct diurnal variation, the amount 

 of carbon dioxide being greater at night. Armstrong's - experiments 

 made at Grasmere in summer-time gave '0296 per cent for the day 

 and '0330 per cent for the night, and similar results have been obtained 

 by other observers. Miintz and Aubin give '0278 per cent as the 

 universal average ; they noticed '0273 as the mean in the day and 

 0288 in the night. 3 H. T. Brown gives as a result of many determina- 

 tions made in 1898-9, '0285 as the mean and -027 and -030 as the 

 usual limits of variations in summer. 4 Over the sea or in places far 

 from vegetation no such difference can be detected, and the average 

 amount is lower. Schulze, as a mean of nearly three years' daily de- 

 terminations of carbon dioxide in the air at Eostock, found '0292 per 

 cent, the maximum being -0344 per cent and the minimum -0225 per 

 cent. 5 



1 Eecent determinations have almost invariably given lower values for the 

 mean amount in the atmosphere. 



2 Pro. Roy. Soc., 1880, 343. 

 : <Bieder. Zentral., 1883, 469. 



4 Brit. Assn. Report, 1899, Presidential Address, Section B. 

 5 Versuch. Stat., 14, 366. 



