LIME-WATER AND CARBON DIOXIDE. 147 



of lime-water; cork the jar and shake up, when the lime-water 

 will become milky, as in Expt. 147 ; the action being that, firstly, 

 the carbon dioxide gas dissolves in the water present ; and, secondly, 

 the solution so formed instantaneously acts on the lime present in 

 the liquid, so as to form an insoluble solid compound, or precipitate 

 of carbonate of lime, chemically identical with chalk or limestone : 

 at first the particles of this solid remain suspended, giving the 

 appearance of milk ; but by and by they subside, and fall to the 

 bottom as a powder. 



Expt. 153. To turn Water apparently into Milk oy the Breath. 

 The action going on in the lungs of air-breathing animals always 

 results in the formation of carbonic acid gas, which is contained in 

 the exhaled breath; consequently, if you blow a stream of air 

 from the lungs by means of a piece of glass tube through a little 

 lime-water in a goblet, the lime-water will quickly turn milky, 

 precisely as in the last experiment, and for the same reason. In 

 country fairs and such like places, travelling quack doctors and 

 medicine-sellers sometimes " humbug " the unsophisticated yokels 

 by pretending that they have an unfailing means of detecting 

 whether any one is consumptive or not ; they say that if any one 

 blows through their marvellous water by means of a tube, if the 

 lungs are affected the water will become milky; but not if the lungs 

 are sound. A stout healthy-looking confederate or " bonnet " is 

 given a glass of water, and blows through it with no result, this 

 particular glass being simply ordinary spring water; he is then 

 pronounced sound, and is perhaps stated to have been cured a few 

 weeks ago of serious lung-disease by taking the wonderful medicine 

 for sale. Some one of the audience then steps up, and is given a 

 glass of lime-water, which of course turns milky as soon as he 

 blows through it ; the quack then tells him that he is sure to die 

 (which no doubt is true, though not in the sense meant), but that 

 he may derive benefit by purchasing the infallible medicine; 

 which it is needless to say is of no use whatever as a cure for 

 consumption, even if not absolutely harmful for other reasons. 



Expt. 154. To turn Lime-water Milky by means of a Burning 

 Candle. The reason why carbonic acid gas is exhaled from the 

 lungs is, that during the various life actions that go on in the body, 

 fuel (taken into the body in the form of food) is made to undergo 

 chemical changes exactly analogous to those taking place when a 

 candle is burned in the ordinary way, or when coal is consumed in 

 a boiler-fire. In all cases the fuel consumes air (or rather one of 

 the constituents of air called oxygen, Expt. 148), and produces heat, 

 moderate in the case of a living animal, but far more intense 

 in the case of a candle or fire ; whilst the products of the 



