ALKALIMETRY. 247 



acid must be employed). The cork, with the chloride- 

 of-calcium-tube, and the bent tube is then introduced, 

 air-tight, into the neck of the flask, the whole appara- 

 tus accurately weighed, and the orifice of the bent tube 

 perfectly closed with a small cork or with wax. 



The flask is then carefully inclined so that a small 

 quantity of the acid may run out of the tube and de- 

 compose the carbonate. The carbonic acid which is 

 evolved escapes through the chloride-of-calcium-tube, 

 in which any water which may have been carried off 

 with it is retained. No fresh acid is allowed to flow 

 out of the tube until the effervescence caused by the 

 first portion has ceased, and does not recommence upon 

 gentle agitation. When, at length, the effervescence 

 has entirely ceased, so that the salt is completely de- 

 composed, the plug is removed from the small tube 

 and suction applied, by the mouth, to the tube contain- 

 ing chloride of calcium, until the air passing through 

 the flask no longer tastes of carbonic acid. In very 

 exact experiments, a second chloride-of-calcium4ube 

 must be attached to the small bent tube, to retain the 

 moisture of the air. 



1. Potashes. The amount of water is ascertained 

 by heating the specimen, for some time, to about 200. 

 For this purpose from 2 to 5 grms. of potashes may 

 be taken. 



In order to determine immediately, without calcula- 

 tion, the percentage of potassa in carbonate of potassa, 

 by means of the above apparatus, 3.14 grms. of the 

 specimen must be taken. Since 3.14 grms. of pure 

 carbonate of potassa evolve 1.00 grm. of carbonic acid, 

 the number of centigrammes of carbonic acid evolved 

 will represent the percentage of carbonate of potassa. 



2. Soda. 2.41 grms. of soda are employed. This is 

 the quantity of pure carbonate of soda which evolves 

 1.00 grm. of carbonic acid. 



Should caustic soda be contained in the specimen, 



