The Romance of Modern Chemistry

PRODUCTION OF LIGHT AND HEAT bustion, and may be referred to generally as oxidation processes. One of these processes, which, without producing any light, produces a good deal of heat, is the respiration of animals. What goes on in our bodies, through the agency of the lungs and the blood, is neither more nor less than a combustion, in the course of which the carbon com- pounds in the body, the fat, &c., are burned to carbon dioxide and water. It is very easy to show that air expired from the lungs is heavily charged with carbon dioxide. Ordinary fresh air contains so little of this gas that a pint bottle full produces no milkiness when shaken up with a little lime water. But if the air which we breathe or blow out from our lungs is made to bubble through a little lime water, a very marked turbidity appears. Exact measurements have shown that whereas fresh air contains 3 to 4 parts by volume of carbon dioxide in 10,000, the air which issues from the lungs is charged to the extent of 400 to 450 parts carbon dioxide in 10,000. A little carbon dioxide is also given off through the skin, and it is com- puted that the total carbon dioxide evolved by the lungs and skin is about three-quarters of a cubic foot per hour. An ordinary gas burner produces about one and a half cubic feet of carbon dioxide in the same time, so that as far as the contamination of the air in a room is concerned, a gas burner is equal to two men. Another change which comes under the same category as respiration, and which we might describe as a slow combustion, is the rusting of iron. Rusting is the com- bination of the metal with the oxygen of the air, and is thus exactly parallel to the burning of magnesium ribbon, except that it takes so much longer. The total heat evolved 116