64 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



[Vol. 6 



the indicators. Aside from being tedious, this method gave 

 at best only a rough comparison, exhibiting obvious errors 

 and leaving much to the personal equation or opinion of the 

 observer. 



Walpole (10, 10 a ) introduced a logical procedure involv- 

 ing the use of the colored test solution as a shield to com- 

 pensate for the color of the sample under observation. He 

 arranged a simple device which when employed for H ion 

 determination consisted of a blackened frame or support hold- 

 ing four glass cells in two similar columns. Each column con- 

 sists of a cell surmounted by a Nesslerizing tube, and each 

 column is illuminated from a dull white surface below, re- 

 flecting the light upward. In the one column the lower tube 

 contains the colored test fluid or sample plus indicator, and the 

 upper tube water; while in the other column the upper tube 

 contains the standard solution (in that case Sorensen's), and 

 the lower the test fluid as shield. In each column the light 

 passes through the colored sample and through a colorless 

 solution, either one or the other, but not both, containing the 

 indicator. The contents of the tube with standard solution 

 may be changed, or other cells introduced differing slightly 

 in H ion concentration, until, on looking down through the 

 column, an exact match is obtained. Although obviously de- 

 fective optically, this simple tintometer is serviceable. The 

 apparatus has also been used considerably for titration work. 



Independently, Hurwitz, Meyer, and Ostenberg (16) de- 

 vised at about the same time another simple apparatus for 

 the compensation of color when the indicator method of H 

 ion determination is employed. In this, designated a com- 

 parator, the same principle as above is applied, but the stand 

 is so formed that four test-tubes are supported vertically in 



and in the same horizontal plane. The system thus 



consists (1) of one pair of tubes (in the direction of the line of 

 vision) with the nearer tube containing the standard solution 

 and indicator, in front of a " shield' ' tube containing the 

 colored sample; while (2) the other pair of tubes consists 

 of one tube containing the sample and indicator, shielded 

 beyond by a tube of water or of standard solution without 



