70 I. K. Phelps — lodometrio Method for the 



Art. X. — An lodometric Method for the Determination 

 of Carbon Dioxide j by I. K. Phelps. 



[Contributions from the Kent Chemical Laboratory of Yale University. — LL] 



In a recent paper from this laboratory,* it has been shown 

 that carbon dioxide may be estimated with accuracy by absorb- 

 ing it under prescribed conditions in barium hydroxide, wash- 

 ing away the excess of the hydroxide, and converting the 

 precipitated carbonate to the form of the sulphate. The chief 

 difficulty in the process was occasioned by the fact that the 

 barium carbonate precipitated from cold solutions is so finely 

 divided and non-crystalline in character, that the removal of 

 the excess of the hydroxide by filtration is a somewhat delicate 

 and tedious process. The possibility of taking up by iodine 

 the excess of the hydroxide remaining after the precipitation 

 of the carbonate, and then determining the excess of iodine 

 volumetrically, furnished the incentive to the following experi- 

 ments. 



The process, as finally developed, consists of three steps : 

 first, the evolution of the carbon dioxide and its collection in 

 barium hydroxide contained in a partially evacuated fiask ; sec- 

 ondly, the conversion of the excess of the hydroxide to the 

 form of iodide and iodate by adding an excess of iodine ; and 

 thirdly, the titration of the excess of iodine with standard 

 arsenious acid. 



The barium hydroxide solution was prepared for use by fil- 

 tering a cold, saturated solution into a large bottle, from which 

 it was drawn, or pumped by means of the little imjDrovised 

 pump described by Kreider ;f in either event care was taken 

 to feed the air, which took the place in the bottle of the 

 hydroxide removed, through potash bulbs to prevent the 

 introduction of atmospheric carbon dioxide. The solu- 

 tion of barium hydroxide was standardized by drawing 

 80 — 90 cm.^ of decinormal iodine into a glass fiask, provided 

 with a ground-glass stopper carrying an inlet tube reaching 

 nearly to the bottom of the fiask and an outlet tube to which 

 was sealed a Will and Yarrentrapp absorption apparatus, and 

 then introducing an appropriate amount of the barium hydroxide 

 solution either from a burette or from a stoppered funnel 

 which was weighed before and after. An ether wash bottle 

 answers admirably for a standardizing fiask, and with the glass 

 stopper and its attachments replaced by a rubber stopper, 



* This Journal, 1, 101. f Ibid., 1, 132. 



