a 
- 
389 
“were Hetecnined according to ‘Standard Methods of Water Analysis’. 
_ The free carbon dioxide titrations were continued to a faint pink which 
was persistent for 3 min. The hydrogen ion concentration was 
_ determined colorimetrically, using standard buffer solutions which had 
been checked by means of the hydrogen electrode. * * * 
“Tn only one case [out of 63] was the difference between the deter- 
mined and calculated p,+ greater than 0.3, and the mean variation is 
about 0.1. It will also be noted that the wider variations occurred in the 
cases of low bicarbonate content, which is to be expected from the 
assumptions made in the development of the equation. * * * 
“From their experience with the colorimetric P»+ determinations, 
the authors do not feel that determinations can be made much more ac- 
curately than 0.2 P.t+, using open tubes and ordinary methods of trans- 
ferring the test sample to the tube. The effect of aeration of such un- 
_ stable solutions as natural waters should amount to this much or more. 
It is advisable in all cases to make several determinations. 
“The formula cannot be applied to waters which are alkaline to 
phenolphthalein. An attempt was made to develop such an equation, 
but no waters naturally alkaline to phenolphthalein were available for 
checking the calculations. For unusual cases of this kind and cases of 
low bicarbonate content, it may be better to use some more complete and 
more complex equation, such as has been developed by Prideaux (Proc. 
Roy. Soc. London (A) 91, 535).” 
“Equations are developed for calculating H+-ion concentration, in 
which the carbon dioxide and bicarbonate are expressed in the manner 
in which they are ordinarily determined. These equations are less ac- 
curate with low bicarbonate concentrations, and do not apply to waters 
alkaline to phenolphthalein.” 
Taste VIII ~ 
Comparison of calculated H ion concentrations with those determined colori- 
metrically. (Excerpts from a table by Greenfield and Baker.*) 
Res. Free Set, Pp SF ; 
on co, eee det Ph Error Source of sample 
evap. | P. P.M. |"Gac0, F calc. 
375 0.0 154 yt) 8.00 | —.10 Vermilion River 
375 7.0 152 420 7.54 .04 Vermilion River 
375 15.5 152 Trax 7.28 .08 Vermilion River 
375 16.5 152 yal 7.29 mat Vermilion River 
375 29.5 152 6.9 7.05 15 Vermilion River 
384 6.0 100 7.3 7.47 cue, Kankakee River 
384 14.0 100°) |s 27.5 7.18 -08 Kankakee River 
384 25.0 96 6.7 6.94 24 Kankakee River 
206 15.0 44 6.9 6.83 —.07 Ohio River 
206 29.0 44 6.5 6.52 .02 Ohio River 
206 | 30.0 44 6.5 6.52 02 Ohio River 
225 11.0 90 453 7.23 —.07 Miss. River 
* Jour. Industr. and Eng. Chem., Vol. 12 (No. 10), p. 991. 1920. 
