A modified Hellige colorimeter for the comparison of solutions containing two colors

Abstract

By introducing an additional standard wedge in the Hellige colorimeter it has been found possible to greatly extend the usefulness 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 S⊘srensen'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 ± PH 0.02 to 0.04. This covers the most used range in the determination of the hydrogen ion concentration of urine, blood and bacteriological culture media. The phenol red standards also serve excellently for the Marriott alveolar 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 phenolsulphonephthalein 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. With thymol blue standards the determination of the PH of gastric juice may be very easily and quickly made.