The Romance of Modern Chemistry

INVISIBLE SUBSTANCES much more vigorous when pure, undiluted oxygen is supplied. The process of respiration is very similar to the process of combustion, and it will be remembered that in cases of serious illness, and as a last resort, pure oxygen is sometimes supplied to the patient instead of air, in order to support for a little longer the flickering flame of life. A little chip of wood serves very well to show the difference between pure nitrogen, pure oxygen, and the air which is a mixture of both. If the chip is set alight and is then blown out, it continues to glow in the air for some considerable time. When the still glowing chip is thrust into a jar of pure oxygen it at once bursts into flame, whereas if it were thrust into a jar of pure nitrogen it would be immediately and completely ex- tinguished. So we learn that of the two chief constituents of atmospheric air one supports combustion, the other does not. Besides oxygen and nitrogen, there are a number of other gases in the atmosphere, but only in very small amounts. The chief of these are argon, a gas resembling nitrogen, to the extent of 9 volumes in 1000 of air, water vapour in varying amount, and carbon dioxide to the extent of 3 or 4 volumes in 10,000. The last- mentioned gas is being constantly produced by the com- bustion of all sorts of fuel, and in the respiration of animals. Whereas the air which we take into our lungs contains, as has just been said, ‘03 or '04 per cent, of carbon dioxide, expired air contains as much as 3 to 5 per cent, of carbon dioxide and correspondingly less oxygen. Strange to say, this constant enormous production of carbon dioxide does not lead to any increase in the average amount of that gas in the atmospheie, for it is as constantly being removed by the instrumentality of