154 AIR AND LIFE. 



liters of air. This gas is comparatively heavy, and Priestley was cog- 

 nizant of the fact that it is unable to support combustion or respiration. 

 The proportions in air are not uniform and constant ; they vary according 

 to circumstances and places much more than is the case with the other 

 gases. As early as 1827 DeSaussure discovered very marked differences, 

 obtaining as extreme figures 3.15 and 5.74 per 10,000. More recently, 

 Boussingault and Levy, comparing the proportion of carbonic acid in 

 the air of Paris with that in the air of Andilly (a small village some 

 12 rniles from Paris, near Montmorency), found also a notable difference 

 between the two, there being 3.19 (per 10,000) in Paris and 2.99 in 

 Andilly. Again, a somewhat smaller difference has been noticed by 

 Eoscoe and McDougall between the air in Manchester and that of the 

 surrounding country; but at Clermont-Ferrand, in central France, 

 Truchot found 3.15 per 10,000 and but 2.03 at the top of the Puy-de- 

 Dome, a neighboring mountain, and 1.72 at Pic de Sancy, another peak 

 of the same group. 



These instances are enough, we presume, to show that the ratio of car- 

 bonic acid to the total volume of the air varies considerably, much more 

 than that of the two previously mentioned gases, and that this com- 

 ponent is more abundant in cities than in the country. 1 This should not 

 occasion wonder, as the amount of carbonic acid varies according to 

 various circumstances of time and place. For instance, De Saussure 

 noted that it increased during the night and during cloudy weather; 

 its ratio changes with the season, from one year, and even from one 

 month, to another, irregularly, and, in fact, from day to day. Above the 

 ocean the variations are less, and in mid ocean the air is purer than 

 over the continents. The same obtains on high mountains. 



If, instead of considering the composition of air collected in the 

 streets, in the country, or on mountains, we compare rather that which 

 we breathe in dwellings and in all confined spaces where ventilation 

 is more or less deficient, and where organic and inorganic combustions 

 take place, with that which obtains in the open, the differences are still 

 greater. Of course, it should be so. We must not forget that the air 

 which each one of us expels through mouth or nose, at this very 

 moment, contains nearly a hundred times more carbonic acid than was 

 contained in the same air when we inhaled it a few seconds ago. This 

 being the case, it is sufficient to imagine a confined room where one or 

 many persons are sitting; there most certainly, provided the experiment 

 lasts long enough, we shall find many different and increasing propor- 

 tions of carbonic acid. That is, we might were the experiment not 

 self limited. For though, as Pettenkofer has observed, the 0.40 or 0.50 



In Austria, the amount of carbonic acid is about 34.3 liters per 100 cubic meters of 

 air; in Germany it varies between 32 and 34 ; in the desert of Lybia, Von Pettenkofer 

 found from 44 to 49. These are rather high figures. During the expedition for the 

 observation of the transit of Venus, analyses made in different countries gave the 

 following results: Florida, 29.2; Mexico, 27.3; Martinique, 28; Haiti, 27.8; Santa 

 Cruz, 26.6. At Cape Horn, Hyades observed 23.1 and 28.5 as extreme figures. 



