170 



METHODS OF ANALYSIS. 



dioxid is to be absorbed and attach them to the apparatus. In case two Liebig 

 bulbs are employed, one for potassium hydroxid and the other for sulphuric 

 acid to absorb the moisture given up by the potassium hydroxid solution, weigh 

 them separately. If two soda-lime tubes are employed it will be found advan- 

 tageous to weigh them separately and fill the first tube anew when the second 

 tube begins to increase in weight materially. Nearly fill tube B with hydro- 

 chloric acid (sp. gr. 1.1) and place the guard tube C in position. Then start 

 the aspirator at such a rate that the air passes through the Liebig bulb at about 

 the rate of two bubbles per second. Open the stopper of the funnel and allow 



/iSCHOLLJmJ 



FIG. 9. Knorr's apparatus for the determination of carbon dioxid ; A, distilling flask fitted 

 to condenser by a ground-glass stopper. B, Reservoir containing acid. C, Soda-llflfl 

 tube fitted to acid reservoir by a ground-glass stopper. D, Condenser. E, Liebig bull 

 filled with sulphuric acid. F, Liebig bulb with a solution of potassium hydroxid foi 

 the absorption of carbon dioxid and followed by a calcium-chlorid tube. An additional 

 guard tube filled with soda lime should follow the tube F, though not shown in the cud 



the acid to run slowly into the flask, care being taken that the evolution of 

 shall be so gradual as not to materially increase the current through the Liebl 

 bulb. After all the acid has been introduced continue the aspiration and 

 ually heat the contents of the flask to boiling, the bulb in tube B being cl< 

 While the flask is being heated the aspirator tube may be removed, altho\ 

 many analysts prefer when using ground-glass joints to aspirate during tl 

 entire operation. Continue the boiling for a few minutes after the water 

 begun to condense in D, then remove the flame, open the valve in tube B, ai 

 allow the apparatus to cool with continued aspiration. Remove the absoi 

 tubes and weigh. The increase in weight is due to carbon dioxid. 



