THE CHEMISTRY OF THE ATMOSPHERE* . , * ,101 



the same poison tbe poison of human breaths -j 

 but little attention. The bad effects of impevfec 

 tion in places crowded with people do not depend alone on 

 the carbonic anhydride which accumulates, but are due in 

 large measure to a sort of effluvium which is given off from 

 the surface of the bodies of human beings. The precise nat- 

 ure of this miasmatic emanation is not known, but it is 

 shown to be largely organic by the fact that it is destroyed 

 by passing through a flame. The importance of ventilation 

 in rooms which are lighted by gas can not be too strongly 

 insisted upon. When we come to study the chemistry of 

 combustion, you will learn that carbonic anhydride and wa- 

 ter are the chief products of the burning gas. In fact, it is 

 calculated that even two candles of six to the pound pro- 

 duce as much carbonic anhydride per hour as would be gen- 

 erated by the respiration of a man of ordinary size. 



127. Sources of Carbonic Anhydride in the Atmosphere. 

 Carbonic anhydride is constantly poured forth into the at- 

 mosphere chiefly from three sources. 1. All fires and lights 

 produce it. 2. It is breathed out by all animals, from the 

 greatest to the smallest. 3. It is one of the products of de- 

 cay. The two first-named sources we have already noticed. 

 The third will be particularly noticed in another part of this 

 book. You will observe in regard to the first two that 

 while carbonic anhydride is formed the oxygen of the air is 

 at the same time diminished. Indeed, in ordinary combus- 

 tion the carbonic anhydride is made by a union of the oxy- 

 gen of the air with the carbon of the burning substance ; 

 and in respiration the lungs absorb oxygen from the air at 

 the same time that they give out carbonic anhydride. 



128. Chemistry of Leaves. We have stated in 115 that 

 all free air is composed of the same proportions of oxygen 

 and nitrogen and carbonic anhydride; and yet there are 

 processes, as you saw in the last paragraph,which constantly 



