78 



Scientific Proceedings (118). 



as to the mechanism of chemical decomposition or of bacterial 

 disinfection. They both illustrate the operation of the law of mass 

 action. 



The extended report of these experiments will be published 

 soon in the Journal of Bacteriology. 



41 (1788) 



A modified Hellige colorimeter for the comparison of solutions 

 containing two colors. 



By VICTOR C MYERS. 



[From the Laboratory of Pathological Chemistry, New York Post- 

 Graduate Medical School and Hospital, New York City.} 



By introducing an additional standard wedge in the Hellige 

 colorimeter it has been found possible to greatly extend the use- 

 fulness of this instrument. With the instrument thus modified, 

 the determination of the hydrogen ion concentration may be very 

 quickly and accurately made by the colorimetric method, since 

 with the two wedges it is possible to obtain all the shades of color 

 from the acid to the alkaline side of the indicator. To aid in 

 reading, the instrument has been provided with an eyepiece with 

 lens. 



With the aid of SoYensen's phosphate solutions (standards of 

 Ph 5.2 and 7.4 for brom cresol purple and standards of Ph 6.4 and 

 8.4 for phenol red) it is possible to cover the range of Ph 5-3 to 8.3 

 with an accuracy in reading of =b Ph 0.02 to 0.04. This covers the 

 most used range in the determination of the hydrogen ion concen- 

 tration of urine, blood and bacteriological culture media. The 

 phenol red standards also serve excellently for the Marriott alveo- 

 lar carbon dioxide test. 



It is a matter of common observation that it is rarely possible 

 to obtain an exact color match with the standard in the phenol- 

 sulphonephthalein renal function test. By using the acid (yellow) 

 phenol red standard in conjunction with the 'phthalein standard 

 it is always possible to obtain an exact color match. If desired 

 correction may be made for the rather small error introduced by 

 the " off " color. 



