reflected components can also be measured with the aid of a rotating mica compensator of known phase difference. This, too, depends on the optical properties of the m a t e rial. The two magnitudes vary, sometimes over wide limits, with the wave length of the incident light. After making measurements a t several wave lengths, the optical d a t a obtained are used for identification of the mineral.
accuracy is designed into
Pétrographie Thin Sections Adaptation of known techniques to a variety of uses is illustrated b y the use of pétrographie thin sections, .lust because we have such a large number of new techniques, says Dr. R. E. Wright, Shell Chemical Corp., we should not forget the use of old ones. We should remember, and use, the contributions of mineralogists, petrographers, biologists, and others. D r . Wright notes t h a t thin sections of hard or brittle materials are not used extensively by chemists except in specialized fields. Such sections are useful in studying structure and spatial arrangement, chemical and physical changes, variations in composition, numbers of species present in a material, detail in partially opaque specimens, and in studying specimens in a specific orientation. The techniques can be used on a wide variety of substances: abrasive wheels, coal, charcoal, refractories and ceramics, clinkers and slags, glass, scales and deposits, solid raw materials, catalysts, pelleted and molded materials, miscellaneous caked and cemented solids, and m a n y others. Equipment for a nominal amount of the usual types of thin section work need not be elaborate. A single-wheel grinder with interchangeable lapping plates and adjustable speed is sufficient for coarse wet grinding. Final lapping can be done on a flat glass plate. For occasional work, or for a preliminary trial of the technique, even the coarse grinding can be done m a n u ally on a couple of flat steel plates. Usually, the rough starting slice ; can be cut with the corundum glass-cutting wheel with which
QUANTICHEM® COLORIMETRIC ANALYZERS for parts per billion ranges Quantichem analyzers continuously, automatically are performing every step of wet laboratory analyses with unprecedented accuracy and dependability in an increasing number of industrial plants. Here are j u s t two of the several reasons why : • DUAL BEAM OPTICAL SYST E M and the use of two samples per analysis (reference and test) automatically compensates for dust or color in the samples, as well as for any difference in the aging characteristics of the two phototubes in the optical system. This compensation, or zero balancing of the bridge circuit, is made once each cycle, automatically. • M I N U S D E L T A P» pump metering system meters chemical reagents used in the analysis to an accuracy of within one q u a r t e r of one percent ! This metering preci-
sion is unaffected by changes in ambient t e m p e r a t u r e or other environmental variations. All analyzer components are housed in a dust-tight cabinet which has a slight positive pressure inside the cabinet. Plant dirt and grime cannot get into moving p a r t s . We would like to send you more engineering data to show you why Quantichem analyzers are built to take tough usage in industrial plants. Write for Bulletin 1156-1. Milton Roy Company, 1300 E. Mermaid Lane, Philadelphia 18, Pa.
milton
Roy
CHEMICAL INSTRUMENTATION SYSTEMS
Controlled Volume Pumps · Quantichem Analyzers Chemical Feed Systems · pH Instruments
Circle No. 176 on Readers' Service Card
VOL.
32, NO. 2, FEBRUARY 1960
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27 A
