172 FARADAY 



Now you understand the ground of the impropriety of ma$* 

 of the arrangements among the houses of the poorer classes, 

 by which the air is breathed over and over again for the 

 want of a supply, by means of proper ventilation, sufficient 

 to produce a good result. You see how bad the air becomes 

 by a single breathing, so that you can easily understand how 

 essential fresh air is to us. 



To pursue this a little farther, let us see what will happen 

 with lime-water. Here is a globe which contains a little 

 lime-water, and it is so arranged as re- 

 " gards the pipes as to give access to the 

 air within, so that we can ascertain the 

 effect of respired or unrespired air upon 

 it. Of course I can either draw in air 

 (through A), and so make the air that 

 feeds my lungs go through the lime-water, 

 or I can force the air out of my lungs 

 through the tube (B), which goes to the 

 bottom, and so show its effect upon the 

 lime-water. You will observe that how- 

 ever l n * draw the external air into the 

 lime-water and then through it to my 

 lungs, I shall produce no effect upon the water it will 

 not make the lime-water turbid; but if I throw the air 

 from my lungs through the lime-water several times in 

 succession, you see how white and milky the water is get- 

 ting, showing the effect which expired air has had upon 

 it; and now you begin to know that the atmosphere which 

 we have spoiled by respiration is spoiled by carbonic acid, 

 for you see it here in contact with the lime-water. 



I have here two bottles, one containing lime-water and the 

 other common water, and tubes which pass into the bottles 

 and connect them. The apparatus is very rough, but it is 

 useful notwithstanding. If I take these two bottles, in- 

 haling here and exhaling there, the arrangement of the tubes 

 will prevent the air going backward. The air coming in 

 will go to my mouth and lungs, and in going out will pass 

 through the lime-water, so that I can go on breathing, and 

 making an experiment very refined in its nature and very 

 good in its results. You will observe that the good air has 



