SODA-WATER SYPHONS. 



75 



, , 1T , , , 

 39 ' Soda-Water Syphon. 



When a gas and a liquid are brought together, the liquid 

 generally dissolves more or less of the gas, forming a solution 

 thereof ; several such solutions have already been used in the ex- 

 periments above described, for ex- 

 ample, solution of hydrochloric acid 

 gas (Expt. 10) and solution of 

 sulphuretted hydrogen (Expt. 12). 

 Ordinary aerated water (soda-water) 

 is a solution of carbon dioxide or 

 carbonic acid gas in water. When 

 the cork of the bottle is taken out, 

 the liquid effervesces violently; 

 this is because the solution has been 

 made under the influence of a con- 

 siderable degree of pressure, which 

 enables the water to dissolve much 

 more of the gas than it otherwise 

 could do. The bottle is filled with 

 the fluid solution and corked by 

 a peculiar kind of machine whilst 

 this pressure is maintained, so that the liquid in the corked 

 bottle is still under pressure ; for which reason, soda-water bottles 

 sometimes burst, especially when kept in a warm place, which 

 tends to increase the internal pressure. When the cork 

 is extracted the pressure is relieved, and as there is 

 more gas present than the water can permanently dis- 

 solve at the ordinary atmospheric pressure, the surplus 

 escapes as gas with effervescence, just as a solution of a 

 solid when saturated hot deposits some of the solid in 

 crystals on cooling (Chapter V.), and just as air satu- 

 rated with moisture deposits some of that moisture as 

 dew on cooling (Expt. 43). Precisely the same remarks 

 apply to aerated water kept in siphons ; instead of a 

 cork, these are fitted with a glass tube arranged like a 

 feeding-bottle, with a valve at the top worked by a 

 handle or trigger (fig 39). On pressing the trigger the 

 valve is opened, and the pressure inside forces out the 

 liquid, which passes up the tube and through the valve 

 and so out of the nozzle. 



Expt. 71. To show that Soda-Water Gas extin- 

 guishes a Candle. Get a large tumbler or a wide- 

 mouthed quart bottle, or better still, a glass cylinder, such as that 

 represented in fig. 40, capable of being covered by a glass plate, and 

 holding about a quart. Uncork a bottle of soda-water, and whilst 



