A NEW AND SIMPLIFIED COLORIMETER ESPECIALLY DESIGNED FOR THE COLORIMETRIC ESTIMATION OF MANGANESE BY THE PERIODATE METHOD* G . FREDERIC~ SI.WIHAND V. R. SULLIVAN, UNNERSITYOP ILLINOIS, URBANA, ILLINOIS
Of the large number and varied design of colorimeters a t present available both of foreign and domestic manufacture, most types are of the precision classification and are accordingly expensive. In some cases the tendency toward an elaboration of design and the installation of precision optical attachments results from the practice of adapting the instrument to both branches of photometric analysis, namely, colorimetry, and nephelometry. Many illustrations of colorimetric analytical methods show that within the proper limits of color intensity and ratios of comparison a definite proportionality exists between the color produced and the concentration of the color-producing ingredient. Beer's law in such cases applies unmodified. In the case of nephelometric investigations results have been obtained using certain types of instruments which indicate, a t variance to Raleigh's law, that the intensity of diffracted light emitted by a Tyndall strip by two turbid solutions is not proportional to their concentrations. Kleinmann (1)has shown that a t least in the case of some nephelometric comparisons the exceptions to Raleigh's law are brought about by defects in instrument design. An instrument free from these defects was designed omitting the extension of its use to colorimetric photochemical observations. It is accordingly, therefore, appropriate to eliminate nephelometric applications from consideration in the design of colorimeters in the interests of simplicity and economy. A further congderation contributing to the cost of the various existing colorimeters results from the praiseworthy installation of conveniences of adjustment and graduation together with provision for restful observational equipment to aid in recording results as well as calculation of the same. For an instrument to be used continually and over extended periods of a single observer's laboratory time such improved and accordingly expensive colorimeters are of great service. Such elaborate design is not, however, a necessity in the case of a unit of general laboratory equipment of which the use is not continuous. For such a case, a demand exists for a simple, rugged, economical, and withal accurate, general-utility laboratory-model colorimeter. The object of the present paper is the description of the design and construction of such a colorimeter and the demonstration of its application to the determination of manganese by the colorimetric periodate method of Willard and Greathouse (2). Experimental data included the comparison of results obtained using the newly designed colorirneter and the Duboscq colorimeter-nephelometer (3). 'Presented before the Division of Chemical Education of the A. C. S. at New Orleans. Mar. 29. 1932. 1461
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JOURNAL O F CHEMICAL EDUCATION
AUGUST,1932
General Apparatus Design The side-view elevation of the assembled apparatus is shown in Figure 1. The same view with the colorimeter partially dismantled is shown in Figure 2. Line drawings showing details of construction and assembly are shown in Figure 3. The colorimeter consists essentially of three parts: (1) the frame supporting the colorimeter tubes, reflecting mirror, and detachable front plate, (2) the colorimeter tubes, and (3) the removable periscope observation collimator. These three units consisting of- five pieces are so designed as t o fit together using lugs instead I;J
