G. H. PARKER 



691 



no attention was given to the slight increase of density that must 

 have ensued in the course of a test by introducing gas into an appara- 

 tus ah-eady filled with air at atmospheric pressure. 



The indicator used in these tests was an aqueous solution of 

 phenolsulfonephthalein (Hynson, Westcott, and Dunning), and the 

 times in seconds necessary to change its tint from that characteristic 

 for pH 7.78 to 7.36 (Osterhout and Haas, 1918), at the four con- 

 centrations of carbon dioxide used, are given in Table I. 



The steps necessary to determine the amount of pure carbon 

 dioxide in ten-thousandths of a milligram delivered per second to 



TABLE I. 



Times in Seconds Needed to Change a Stnndard Solution of Indicator {Phenol- 

 sulfonephthalein) from pH 7.78 to 7.36 by the Introduction into the Osterhout 

 Respiratory Apparatus of Four Mixtures of Gases Containing Respectively 

 0.4, 1, 2, and 4 Per Cent of Carbon Dioxide. 



the apparatus are shown in Table II. In the table are given: (A) 

 the percentage concentration of the carbon dioxide mixture, followed 

 by the time (B) required to deliver 10 cc. of this mixture to the 

 apparatus. By dividing 10 cc. by the number of seconds needed to 

 deliver that amount of gas to the apparatus, the volume of gas 

 delivered per second was found (C). By multiplying this volume 

 by the appropriate per cent indicating the proportion of the impure 

 carbon dioxide contained in the given mixture, the several volumes 

 of impure carbon dioxide delivered were determined (D). By 

 absorbing with sodium hydroxide in a graduated tube a sample of 



