Hellige comparator

Comparator Use either the standard Hellige comparator (Orbeco, Catalog No. 607) or the pocket comparator with prism attachment (Orbeco, Catalog No. 605AHT). The comparator should be illuminated with a 100-W frosted lamp placed 6 in. from the rear opal glass of the comparator and mounted so that direct rays from the lamp do not shine into the operator s eyes. 

Comparator Tubes Use the precision-bored square tubes with a 13-mm viewing depth that are supplied with the Hellige comparator. Suitable tubes are also available from other apparatus suppliers (e.g., Thomas Scientific). 

The Hellige turbidimeter is also a variable depth type of instrument using visual detection. A combination of vertical and horizontal illumination of die sample and a split ocular permit the eye to function merely to compare the intensities of two images simultaneously appearing in the ocular. This is a special form of double-beam operation, and the intensity emitted by the light source need not be extremely constant from one sample to another. Adjustment is made of a slit in the path of the direct, or vertical, illumination of the sample, and the calibration curve consists of a plot of this slit opening v,r. concentration. 

Color of the uncured epoxy resins is an indication of contamination, incomplete polymerization, oxidation, and other factors. Aromatic resins with lower molecular weight generally have better (lower) color. Color is usually reported in terms of the Gardner liquid color standards or the Hellige color comparator or by means of the APHA number. 

Figure 6. Unsaturated galacturonides as nonenzymatic browning precursors. Hellige units are obtained by comparing color of sample with color of tinted glass discs according to the Lovibond principle. (Reproduced with permission from ref. 39. Copyright 1988 Springer.)...

Hellige system or comparator n. Standard instrument for color determination of liquids such as varnishes, oils, etc., based on comparisons which are made against a series of discs of colored glass, and which are carefully graded. 

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