THE
EDITORS' COLUMN rpHE
TENTH
EDITION
of
HI
"Official
* .Methods of Analysis" has r e cently been published b y the Association of Official Analytical Chemists (formerly known as t h e Association of Official Agricultural Chemists). The current edition contains 125 more pages t h a n t h e last edition. Changes in t h e official methods significantly reflect both t h e changing technologies of t h e different industries a n d t h e advances in analytical science. T h e new edition shows pai ticularly increased activities in the areas of pesticides, drugs, fats, and oils. Food additives appear for the first time in t h e T e n t h Edition— three methods were adopted, including one developed in cooperation with the A S T M for extractives from packaging materials. A cooperative arrangement with t h e American Society of Brewing Chemists supplied seven new methods for beer a n d brewing materials. Eight new methods were adopted for oils and fats, reflecting a high degree of interest in foods from a health standpoint. T h e majority of t h e new methods listed in t h e T e n t h Edition involve the use of spectrometry or chromatography—which reveals t h e trend in methodology for t h e methods adopted over t h e p a s t five vears. Improved Method for Standardizing Fluorescent Lamp Colors An improved method for standardizing fluorescent lamp colors was recently developed at the NBS Institute for Basic Standards by H. K. Hammond, M. J. McDonald, and D. R. Charlton. In this method, a spectroradiometer is employed to determine the chromaticitics of the lamps. A sphere, 20 cm. in di-
PRECISION RESEARCH
NANOLITER
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Circle No. 138 on Readers' Service Card
VOL.
3 8 , N O . 1 , JANUARY 1 9 6 6
·
89 A
EDITORS' COLUMN ameter, coated with b a r i u m sulfate, and having a 7.6-cm. aperture, is the collecting element; a doublegrating monochromator is the dis persing element. T h e entrance a n d exit slits of the monochromator are equal and are set to pass a spectral band of 5.6 m^. T h e detector is an S-20 multiplier-type phototube with high sensitivity in the visible spec t r u m . Light entering the sphere's aperture is diffusely reflected by the inner surface of the sphere and then passed through the monochromator to the detector. T h e detector cur rent is indicated on a picoammeter with digital r e a d o u t ; a flatplate re corder is also used. An incandescent lamp operated at, a known color t e m p e r a t u r e is used as the s t a n d a r d light source. T o carry o u t a calibration, t h e fluo rescent lamp under test is mounted on a bench above the aperture in t h e sphere. T h e incandescent lamp is mounted to one side of the sphere on a horizontal line through the sphere's center. The fluorescent lamp is installed in a draft-free en closure and operated a t a constant current. B o t h lamps are operated continuously, a n d light shields are used to prevent interreflection. T h e r a d i a n t flux from each source is measured at lO-m,». intervals over the spectral range from 400 to 700 ηΐμ. T h e sphere is r o t a t e d m a n u ally 90 degrees a t each wavelength interval to obtain a measure of t h e relative spectral irradiance of the fluorescent lamp and of the incan descent l a m p . T h e intensity of each mercury line is computed from the area under the curve in the r e gion of the line. T h e chromaticity coordinates of the lamp are then computed. T h e instrument has been used to recalibrate the fluorescent lamps maintained a t N B S as color stand ards. T h e values thus found for chromaticity coordinates did not differ m a r k e d l y from those pre viously derived with a visual cali bration m e t h o d ; however, the new values were reproducible to a higher degree of precision t h a n could be achieved visually.
ATOMIC ABSORPTION SPECTROPHOTOMETER
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UNIGALVOS • HIGH
SENSITIVITY
• ACCURACY
± 1% F . S . D .
• LINEAR RESPONSE
± 1%
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STABILITY
• U N I Q U E S U S P E N S I O N LOCK • OVER 7000 I N U S E
INTERNATIONAL SALES ASSOCIATES 115 E a s t M a p l e A v e . , L a n g h o r n e , P a .
(215) S K - 7 - 9 8 7 4
See Buyers' Guide for all products/sales offices. Circle Nos. 88, 89 on Readers' Service Card
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Taylor Instruments MEAN ACCURACY FIRST Circle No. 49 on Readers' Service Card VOL. 3 8 , N O . 1 , JANUARY 1 9 6 6 ·
91
A
