ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 211 



stuffs from the atmosphere itself, a great advance will have been made 

 in agriculture and in the cheapening of food. 



CARBON DIOXIDE. 



Carbonic acid gas, or carbon dioxide, is found in small quantities 

 everywhere in the air, and in about the same proportion at 11,000 feet 

 as at the sea level. It is a colorless, transparent gas and does not sup- 

 port combustion or animal life. At 0° C. it may be liquefied under a 

 pressure of 38.5 atmospheres. When liquefied and then allowed to 

 escape it freezes into a snow-white solid in the air, and in a vessel 

 under the vacuum of the air pump freezes into a transparent mass 

 like ice. 



One liter of carbonic dioxide at 0° C. and 760 mm. pressure weighs 

 1.97714, nearly double the weight of air, taken as 1. 



At the ordinary temperature and pressure water dissolves about its 

 own volume of the gas. Dissolved in rain it exerts in the course of time 

 a very powerful disintegrating effect on rocks and minerals, so that 

 the crust of the earth is greatly modified by the constant action of the 

 solution. 



The chief sources of carbonic dioxide in the air are the respiration of 

 animals and the burning of fuel. A large quantity emerges from the 

 earth in certain places, as in the Poison Valley of Java, and in many 

 mineral springs, where it effervesces out of water escaping from pressure. 



Saussure found the amount per cent in a wood near Geneva to be 

 0.0501 in the day and 0.057G at night; in January, 0.0423; in August, 

 0.0568. In Geneva he found an average amount of 0.0468, compared 

 with 0.0437 in the wood. 



Schulze, Reiset, Levy, Armstrong, and Muntz, in different places, 

 made several thousand observations, and the mean of all these shows 

 during the day 0.0299, and during the night 0.0317. Reiset's long con- 

 tinued observations in the country 4 miles from Dieppe gave an average 

 of 0.02942 ; and in June, above the crop of red trefoil, 0.02898 ; in July, 

 above barley, 0.02829; near a flock of sheep, 0.03178. 



Thorpe's very carefully conducted experiments agree well with the 

 above values, and give for the air over the sea 0.03011. Armstrong, at 

 Grasmere, obtained during the day 0.0296, and during the night 0.033. 

 At the Montsouris Observatory the mean during 1877-1882 was 0.03. 



In an unventilated barrack the following amounts have been re- 

 corded as the result of careful observations: 0.1242, 0.189, 0.195; in 

 a hospital at ISTetley, 0.06 to 0.08; in the General Hospital, Madrid, 

 0.32 to 0.43; in a boys' school, 4,640 cubic feet and 67 boys, 0.31; in a 

 crowded meeting, 0.365; in a schoolroom at Madrid, 10,400 cubic feet 

 and 70 girls, 0.723; in a stable at Hilsea, cubic space 655 feet per 

 horse, 0.1053. 



It is not easily explained why the normal amount of carbonic dioxide 

 in the free air has been so long assumed in scientific articles and text- 

 books as 0.04 per cent, or 4 volumes per 10,000, when the best recent 



