CARBONIC ACID. 341 



We can easily prove the existence of carbonic acid gas as exhaled from 

 the lungs. Suppose we take a glass and fill it partly with clear lime-water; 

 bieathe through a glass tube into the water in the glass, and very quickly 

 you will perceive that the lime-water is becoming cloudy and turbid. This 

 cloudiness is due to the presence of chalk, which has been produced by the 

 action of the carbonic acid gas in the lime-water. This is a well known and 

 always interesting experiment, because it leads up to the vital question of 

 our existence, and the functions of breathing and living. 



A popular writer once wrote a book entitled, " Is Life Worth Living ?" 

 and a witty commentator replied to the implied question by saying, " It 

 depends upon the liver" This was felt to be true by many people who 

 suffer, but the scientific man will go farther, and tell you it depends upon the 

 air you breathe, and on the carbonic acid you can raise to create heat, 

 animal heat, which is so essential to our well-being. We are always burning ; 

 a furnace is within us, never ceasing to burn without visible combustion. We 

 are generating heat by means of the blood. We know that we inhale air into 

 the lungs, and probably are aware that the air so received parts with the 

 oxygen to renew the blood. The nitrogen dilutes the oxygen, for if we 

 inhaled a less-mixed air we should either be burnt up or become lunatics, as 

 light-headed as when inhaling " laughing-gas." This beautifully graduated 

 mixture is taken into our bodies, the oxygen renews the blood and gives it 

 its bright red colour ; the carbon which exists in all our bodies is cold and 

 dead when not so vivified by oxygen. The carbonic acid given off produces 

 heat, and our bodies are warm. But when the action ceases we become cold, 

 we die away, and cease to live. Man's life exemplifies a taper burning ; 

 the carbon waste is consumed as the wax is, and when the candle burns 

 away it dies ! It is a beautiful study, full of suggestiveness to all who care to 

 study the great facts of Nature, which works by the same means in all 

 matter. We will refer to plants presently, after having proved by experi- 

 ment the existence of nitrogen in the air. 



Rutherford experimented very cruelly upon a bird, which he placed 

 beneath a glass shade, and there let it remain in the carbonic acid exhaled 

 from its lungs, till the oxygen being at length all consumed by the bird, it 

 died. When the atmosphere had been chemically purified by a solution 

 of caustic potash, another bird was introduced, but though it lived for some 

 time, it did not exist so long as the first. Again the air was deprived of 

 the carbonic acid, and a third bird was introduced. The experiment was 

 thus repeated, till at length a bird was placed beneath the receiver, and it 

 perished at once. This is at once a cruel and clumsy method of making 

 an experiment, which can be more pleasantly and satisfactorily practised by 

 burning some substance in the air beneath the glass. Phosphorus, having 

 a great affinity for oxygen, is usually chosen. The experiment can be 

 performed as follows with a taper, but the phosphorus is a better exponent. 



Let us take a shallow basin with some water in it, a cork or small 

 plate floating upon the water, and in the plate a piece of phosphorus. 



