CARBONIC ACID. 371 



is easily attached firmly to the floor. In this brass block are cavities 

 for the two valves, one opening inwards from the pipe, B, the other 

 outwards, towards the pipe, C. The pipe, B, communicates with a 

 reservoir of gas which the condenser draws in, and forces through 

 the other pipe into a strong copper vessel containing the water. The 

 front part is represented as removed in order to expose the inside to 

 inspection." 



" If due care be taken to expel all the air in the vessel before the 

 impregnation is commenced, the water will take up as many times its 

 bulk of gas, as the pressure employed exceeds that of the atmosphere." 



" When duly saturated, the water may be withdrawn at pleasure, 

 by means of the syphon, D, of which one leg descends from the 

 vertex of the vessel, to the bottom, while the other is conveniently 

 situated for filling a goblet." 



(Z.) The gas washed to free it from any sulphuric acid, and passed 

 up into litmus infusion, reddens it fugaciously. 



(m.) Liquid* carbonic acid gives up its gas by boiling , and by 

 being placed under the exhausted receiver. 



(n.) Litmus water, reddened by this acid, is restored by air pump 

 exhaustion, or by boiling. -\ This gas is liberated from water by 

 freezing, which gives the fluid a spongy appearance. 



(o.) Lime water is a test of carbonic acid; it is applied by pour- 

 ing the liquid acid into it by suffering the gas to pass into a tall in- 

 verted tube closed at the top and filled with lime water, or by re- 

 ceiving the gas in a bottle and washing it with lime water. 



(p.) An excess of carbonic acid redissolves the precipitate, and 

 then more lime water precipitates it again, and so on without limit. 



(q.) Burn a candle, a stick, or any common combustible, in a bot- 

 tle of air or oxygen gas, and examine by lime water for carbonic 

 acid ; if present there will be a milky precipitate. 



(r.) Carbon is a principle of those substances which, by burning, 

 give a gas not rapidly absorbed by water, and which precipitates lime 

 water; the precipitate being soluble in muriatic acid, with effervescence. 



(s.) This gas is an antiseptic, and therefore useful in putrid dis- 

 eases, and externally in ulcers. Cataplasms are made with yeast 

 and other fermenting materials. 



(t.) Meat suspended in carbonic acid, especially if the gas be 

 frequently renewed, keeps much longer than in common air. 



(u.) Carbonic acid promotes vegetation, especially when in the 

 liquid form and applied to the roots ; also, as an atmosphere, pro- 



* At a common temperature and pressure, water absorbs its own volume of gas ; 

 twice its volume under a double pressure, and so on in the same ratio. 



t Tincture of alkanet diluted and slightly blued by ammonia, is decidedly redden- 

 ed when agitated in a vial with carbonic acid gas. 



When the above solution is boiled so as to expel the carbonic acid, it resumes its 

 original blue color. 



