§ 60. CARCONIC ACID. 81 



upwards. Short pieces of tliick- walled rubber tubing tbat 

 will lit snugly on the outer termination of the calcic chlo- 

 ride tube and the acid reservoir, at d and e, are slipped 

 over tbem, and these rubber tubes are then provided with 

 well-fitting stoppers of glass rod ; all these joints must 

 be air-tight. 



The carbonate is weighed as usual in the flask, A, bet- 

 ter in the form of small fragments than of a powder, the 

 acid reservoir is nearly filled with hydi'ochloric acid 

 (Sp. Gr. = 1.1), the, apparatus is put together, and, after 

 the glass-rod stoppers are removed, it is. connected with a 

 generator of carbonic acid, and a rather rapid current of 

 vv'ashed gas is passed through for about 15 minutes, or 

 until the acid in the reservoir is saturated, and the air 

 displaced in the flask ; then stop the opening at d^ discon- 

 nect- the apparatus from the generator, and close the open- 

 ing at e, with care in this and all subsequent operations to 

 handle tlie apparatus so as not to change its temperature. 



Weigh it immediately, loosen the stopper at 6?, and in- 

 cline the whole so that the acid will flow over, little by 

 little, and i^roduce a slow decomposition of the carbonate. 

 Close d again when the decomposition is ended, let the 

 apparatus stand about 15 minutes, to be sure that it is 

 cool, pass well-dried carbonic acid gas in again for about 

 a minute, in the same manner as at first, and finally weigh 

 it after closing dv and e. 



h. For the second method the following form of ap- 

 paratus is highly recommended by Fresenius. 



In the apparatus represented by this figure e contains 

 soda lime or caustic potash in pieces, a is a flask of about 

 300 c.c. capacity, the arm / of the first U tube is filled 

 with fused calcic chloride, and the arm/ with pumice-stone 

 that has been soaked in a concentrated solution of cupric 

 sulphate, dried, and gently ignited so as to drive out the 

 water of crystallization of the salt ; g contains pieces of 

 glass, 6 to 10 drops of concentrated sulphuric acid in the 

 4* 



