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Meetthe ideal aIboratorymicrscope.The Leitz Dialux 20.With superb NPL fluotar objectivesandoptimum modularityr.Fiulotar Objectives

The Dialux 20 is the first of anew generation ofprecision Leitzgmicroscopes with innovativefluotar objectives. Made of glassspecially developed by Leitz, thefluotar objectives produce imageswith critical sharpness and highcontrast throughout the entire fieldofview, even at full illuminationaperture.Universal Condenser

Without vertical adjustment,the universal condenser maintainsperfect Koehler illumination dur-ing magnificationchange for allobjectives aslow as the FL1.6:1. Truly uni-versal, it can beused for bright-field, darkfield, andboth phase and differ-ential interference contrast.Sturdy, Versatile Stand

The Dialux 20 standprovides precision controland virtually eliminatesexternal vibration, evenunder the weight ofadditional ac-cessories. Theenclosed topand bottomprotect the inte-

rior elements from dust. Modular indesign, the Dialux 20 will maintainits compatibility with all existingand future Leitz accessories. Formaximum flexibility, the Dialux 20comes equipped with interchange-able lamp housing for light sourcesup to 100W. For routine use, theDialux 20 EB Model has a built-in20W halogen lamp and voltmeter.Hulman-Engineering forEase of

Operation andFatigue Reduction

The color-codedobjectives have*engraved outersleeves that can berotated so that theymiiiinr'F always face theIW7 \ observer for

quick identification. The fie adjust-ment conveniently moves the objectstage over the entire 35mm rangeof coarse adjustment. For photowork, the beam-splitting systembuilt into the phototube can be setfor total binocular observation, orfor simultaneous observation andpicture-taking. The Dialux 20: Thelatest example in Leitz' 125 yearhistory of dedication to advancedmicroscopy.

For more information pleasemail the coupon below.

Leitzmeans precision.

_ ~Worldwider ------ -I

E. Leitz SCIS-4Rockleigh, N.J. 07647Please send me information on theLeitz Dialux 20 microscope.

NAME

ADDRESS

CITY

STATE ZIPL.

I// '1q

4 MAY 1979 455

Man has been plating chromium for over a cen-tury ... even though puzzled by the electrochemistryinvolved.

For example, the normal process uses a bathcontaining Cr+6 ions. During plating, the Cr+6 ionsreduce to Cr+3 and then to metallic Cr. Now you mightwonder: If the process goes through the Cr+3 stageanyway, why not start with those ions? Well, strangelyenough, if you try, the process won't work unlessconsiderably modified.

Our scientists have long been intrigued by thisenigma here at the General Motors ResearchLaboratories. And they now believe they've not onlyexplained the Cr+3 mystery, but developed a correcttheory of the entire chromium plating process as well.

By analyzing polarization curves obtained fromcarefully designed experiments, they concluded that:

Cr+3 (GREEN BALL) 0Starting with Crt3 failsBOUND BY WATER MOLECULESAS A STABLE COMPLEX ION because it immediately

forms a stable complexwith water molecules (seedrawing) from which Crcannot be deposited.* Starting with Cr+6 suc-ceeds because duringreduction a chemical filmforms around the cathode(the part being plated); andsince Cr+3 is bound in thatfim, it does not react with

water... but, instead, plates out as chromium metal.

From a murkU

platinga bath.

new answers.

Co

0R

-1.1

Apparent Current Density x 10-4 (amp/Cm2)

Our researchers have, in fact, determined all 10steps that take place as Cr+6 reduces to bright Cr,pinpointed the step at which catalysis begins, andidentfied the active catalyst. (It's not the sulifate ion, ascommonly held, but the bisulfate ion.)

So have we merely solved a stubborn puzzle? No.More than that, we've gained important new insight toguide us toward a more efficent chromium electroplatingprocess.

E- General MotorsResearch LaboratoriesWarren, Michigan 48090

We currently have openings for Ph.D.s in engineeringor the physical, mathematical, or biomedical sciences. Ifinterested, please sendyour resume to: GMR Personnel, Dept.515. An Equal Opportunity Employer.

SCIENCE, VOL. 204

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