1 86 



COMPOSITION OF ATMOSPHERIC AIR. 



engine) continually renews the air within the chamber. The air passes into a vessel, b, filled 

 with pumice-stone saturated with sulphuric acid, in which it is dried ; it then passes through a 

 large gas-meter, c, which measures the total amount of the air passing through it. After the air 

 is measured, it is emptied outwards by means of the pump, PPj. From the chief exit tube, x, 

 of the chamber provided with a small manometer, q, a narrow laterally placed tube, n, passes 

 conducting a small secondary stream, which is chemically investigated. This current passes 

 through the suction-apparatus, MM] (constructed on the principle of Muller's mercurial valve, 

 and driven by a steam-engine). Before reaching this apparatus, the air passes through the 

 bulb, K, filled with sulphuric acid, whose increase in weight indicates the amount of watery 

 vapour. After passing through MM 1( it goes through the tube, R, filled with baryta solution, 



which takes up C0 2 . The quantity of air which passes through the accessory current, n, is 



Respiration apparatus of v. Pettenkofer 



146. 

 chamber 



person experimented on ; x, exit 



per 

 tube with manometer, q ; b, vessel with sulphuric acid ; C, gas-meter ; PP 1} pump ; n 

 secondary current, with, k, bulb ; MM], suction apparatus ; u, gas-meter ; N, stream for 

 investigating air before it enters Z. 



measured by the small gas-meter, u, from which it passes outwards. The second accessory 

 stream, N, enables us to investigate the air before it enters the chamber, and it is arranged in 

 exactly the same way as n. The increase of C0 2 and H 2 in the accessory stream, n {i.e., more 

 than in Is), indicates the amount of C0 2 given off by the person in the chamber, Z. 



123. COMPOSITION OF ATMOSPHERIC AIR. 



Gas. 



o, 



N, 

 CO, 



By Weight. 

 23-015 

 76-985 



1. Dry Air contains 



By Volume. 

 20 96 

 79-02 

 0-03-0-034 



2. Aqueous vapour is always present in the air, but it varies greatly in amount, 

 and generally increases with the increase of the temperature of the air. We 

 distinguish (a) the absolute moisture, i.e., the quantity of watery vapour which a 

 volume of air contains in the form of vapour ; and (6) the relative moisture, i.e., 

 the amount of watery vapour which a volume of air contains with respect to its 

 temperature. 



Experience shows that people generally can breathe most comfortably in an atmosphere which 

 not completely saturated with aqueous vapour according to its temperature, Dut is only 



