55] 



Estimation of Carbon Dioxide 



35 



For use by students, however, the apparatus shown in fig. 22 

 is to be recommended. 



a is an 8-oz. conical flask, into which the weighed quantity 

 of carbonate is placed. Through the stopper of the flask pass 

 two tubes, one communicating with a reservoir of dilute hydro- 

 chloric acid, b, and the other with a series of tubes, d, e, / 

 and g, intended to purify and absorb the C0 2 formed. 



At the end of this series of tubes is some form of aspirator, 

 by means of which a current of pure dry air may be caused to 

 pass through the whole apparatus. 



Preparation of the apparatus : 



First of all, the different U tubes must be carefully cleaned 

 and filled as follows : 



Tube f This is the tube which is destined to absorb the 

 C0 2 evolved in the flask a. The form of tube shown in the 

 figure is very convenient, as the two 

 stopcocks enable the operator to shut 

 off its contents from the air whilst 

 weighing. When the tube is perfectly 

 clean and dry, a loose plug of cotton 

 wool is pushed down one side to the 

 position 1, fig. 23. The part 3, fig. 23, 

 is filled with granulated soda lime which 

 has been sifted free from dust, and the 

 part 2, fig. 23, with granular calcium 

 chloride. Two little plugs of cotton wool 

 are then placed at the ends, 4, 4, fig. 23, and the glass stop- 

 cocks inserted. 



Fig. 23. 



solution. Then comes a U tube containing soda-lime, and serving as a 

 guard. 



The last three Geissler bulbs constitute the weighable portion of the 

 apparatus. Perfectly dry air plus carbonic acid enters these, and perfectly 

 dry air alone escapes. The increase in weight gives the amount of car- 

 bonic acid. 



D2 



