Determination of Carbon Dioxide, 71 



answers the purpose of the absorption flask described later. 

 The glass stopper is introduced, the inlet being closed by a 

 rubber cap, and the absorption apparatus is charged with a solu- 

 tion of potassium iodide, to hinder the escape of iodine. The 

 solution was brought to a boil, then cooled and the excess of 

 iodine determined by decinormal arsenious acid. It is assumed 

 that the iodine lost acted on barium hydroxide according to the 

 equation : 



6BaO,H, + 6l, = Ba(I03), + 5BaI, + 6H,0. 



It was found necessary to boil the solution because of the 

 formation of traces of the hypoiodite, which is broken up into 

 iodide and iodate only by boiling, but which, if left unchanged, 

 acts subsequently on the arsenious acid used in titrating the 

 free iodine. 



The apparatus which I have found most convenient for 

 evolving the carbon dioxide from the carbonate consisted of a 

 wide-mouthed flask of about 75 cm.^ capacity, furnished with a 

 doubly perforated stopper carrying a separating funnel for 

 the introduction of acid into the flask, and a tube of 0*7 cm. 

 internal diameter, which is expanded to a small bulb just above 

 the stopper, to carry off the gas. This exit tube was joined by 

 a rubber connector to a tube which passed through the rubber 

 stopper, closing the absorption flask (the ether wash bottle used 

 in standardizing the barium hydroxide solution described 

 above), and which ended in a valve preferably of the Kreider 

 pattern.^ This valve was enclosed in a larger tube reaching 

 nearly to the bottom of the absorption flask. Through a sec- 

 ond hole in the stopper of the absorption flask passed a glass 

 tube closed by a rubber connector and screw pinch cock. 



In making a determination of carbon dioxide, the carbonate 

 was introduced in weighed portions into the boiling flask. 

 Barium hydroxide solution, in amount from 7 — 10 cm.^ more 

 than actually necessary to precipitate the carbon dioxide, was 

 drawn into the absorption flask, which was then connected with 

 the boiling flask, as described above. The stop-cock of the 

 separating funnel was shut off and the flasks evacuated by con- 

 necting the exit tube of the absorption flask with a fllter flask 

 previously pumped out by the water pump, a mercury man- 

 ometer registering the pressure. Exhaustion to a pressure of 

 from 250-300 mm. was found sufficient and easily attainable 

 with the available water pressure in a minute's time. Sufficient 

 phosphoric acid (chosen as a non-volatile acid) to dissolve the 

 carbonate was introduced into the stoppered funnel with about 



*Loc. cit. 



