INSTRUMENTATION by Ralph H.
N e w recording balance features several innovations
Müller
F I S H E R Medalist James Lingane As remarked in San Francisco, a n unexpected earthquake could have wiped out t h e majority of America's experts in electroanalysis. This was an indirect way of saying that every analyst who could possibly make i t hastened t o the Bay area t o honor this fine scientist and congenial fellow. T h e van was augmented b y a n even larger crowd of enthusiastic amateurs, including the Instrumentation Editor. Beckman Medalist Maurice Hasler's fascinating account of t h e contempor a r y state of emission spectroscopy will be awaited, in its printed form, b y all progressive analysts. Those in his audience who did not happen to be experts in t h e field may n o t have realized t h a t this quiet, scholarly address was, in large part, a n autobiography. Hasler, along with others such as R a y nor Churchill, J . L. Saunderson, a n d B. F . Scribner have refined and are refining t h e automatic spectrometer of the quantometer t y p e t o t h e point where it becomes t h e despair of t h e classical professor of analysis. W i t h 10-second exposures, spectrometer outputs can b e fed to digital electronic storage and read into I B M cards. T h e whole job of recording, computation, and interpretation for as many as 18 elements is involved in these techniques. These things are a source of delight t o budget directors who appreciate t h e tremendous savings in time and money. To the scientist, the reward appears in a different light; it means more precision and more information. Berkeley Visited
Figure 1 .
Recording b a l a n c e w i t h r e c o r d i n g a n d a u x i l i a r y control unit
Figure 2 .
Rear v i e w o f r e c o r d e r unit
The charming hills of Berkeley provided a n excellent opportunity to visit the famed Radiation Laboratory with its bevatron, cyclotron, and new high energy linear accelerator. T h e terrain is better suited t o mountain goats, but the exertion is more than well repaid. This is t h e birthplace of californium and berkelium. With its corps of world-famed nuclear physicists a n d chemists, this laboratory, God willing, and extremely short half lives t o t h e contrary notwithstanding, m a y yet give us oaklandium, alcatrazium, a n d pismobeachium. Recording Balance
The Pacific Chemical Exposition, held in conjunction with the ACS meet-
Figure 3 .
Arrestment motor VOL. 30, NO. 7, JULY 1958
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47A
INSTRUMENTATION
Cary Applied
At E a s t m a n
Physics
instrument abstracts Corporation/Pasadena/California
Kodak
Cary Model 14 Spectrophotometer measures absorbance to 7.1 without correction for stray light.
Run A represents che normal check of a Fabry-Perot interference filter similar to those used in densitometry of color films where the passband and shape of the filter curve is important up to densities of 7.0. This particular filter curve showed a nonsymmetrical peak at 639 mu. For a closer examination of this peak a second expanded curve of this wavelength region, Run B, was made in super-position on the first curve.
In the Laboratories of the Eastman Kodak Company interest in absorbance values over seven —less than .00001% transmission—is more than idle curiosity. Recently, Kodak physicists, using one of their Cary Model 14 Spectrophotometers, were pleased to find they could measure densities to 7.1 with out correction for stray light. In contrast, there are numerous instances where months of hard work were wasted because unsuspected stray light of single monochromator instruments caused large errors sometimes even below 1.0 ab sorbance. Double monochromators cost more to design and build. But they provide advan tages that can be had in no other way. Besides low stray light, the double mono chromator adds the dispersion of its sep arate sections and is arranged to cancel severe optical aberrations, giving increased resolution. In the Model 14, a silica prism and a 15,000 line diffraction grating add the higher ultraviolet dispersion and the low stray light of the prism to the excellent visible and infrared dispersion of the grat ing. Each complements the other to produce exceptional performance from 1860 to 26,500 Angstroms. All Cary instruments are truly direct reading. Freedom from stray light provides one of the most dramatic examples of what this can mean to a user, but there are others. Some of the unusual features of Cary Recording Spectrophotometers which con tribute to accuracy by helping avoid correc tions are listed at right.
COUNTER-DIAL WAVELENGTH SCALES-Easily
read, no interpolation, corrections negli gible for most work. MULTIPOT-CORRECTED 100% LINES-A11 Cary
Spectrophotometers have Multipots for compensating sample and reference cell differences, and for compensating mirror unbalances which inevitably occur in time. SPECIAL RECORDER FUNCTIONS AVAILABLE-
Log absorbance recording for qualitative — quantitative analyses. Kubelka—Munk func tion recording for paper and textile dye work. Expanded absorbance or transmission scales for weak absorbers or differential photometry. ACCURATE PHOTOMETERS-Slide wires accu rate to within limits of recorder readability. Photometer accuracy rigidly tested with standard filters. High power pen motor and low friction pen carriage. Constant con trolled pen damping and fast response over entire absorbance range. HIGH ACCURACY ELECTRICAL ZEROING-Spur ious electrical pickup reduced by careful design and testing. PHOTOMETRIC PRECISION TO STATISTICAL
LIMITS—Statistically efficient photometer systems, reaching the theoretical limits achievable with the best modern multiplier phototubes and semiconductor photocells. Complete specifications are available on all Cary Recording Spectrophotometers. Write to Applied Physics Corp., 362 West Colorado Street, Pasadena, California, for Bulletin Al-78.
For further information, circle number 48 A on Readers' Service Can, page 69 A 48
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ANALYTICAL
CHEMISTRY
ing, was small by exposition standards, but was most interesting and well at tended. Here we were able to obtain detailed information and a demonstra tion of t h e new Ainsworth T y p e B R AU recording balance. I n t h e April column, brief, mention of several re cording balances led to an unfortunate mistake. A typographical error using " t h e " instead of " t h e i r " led us to im ply a connection between the instru ment manufactured b y Niagara Elec tron Co. and the Ainsworth instrument. We are told t h a t Niagara Electron buys Ainsworth balances, b u t converts t h e m to suit its m e t h o d of operation. T h e T y p e BR-ATJ recording balance was developed entirely in the Ainsworth Co. and through the courtesy of presi dent G. S. Clayson and F . Bauer we are able to present some of the dis tinctive features of this instrument. Figure 1 shows the recording balance, in which t h e recording and auxiliary control unit appears on the left. T h e unit on the right, t h e balance, is essentially a regular analytical t y p e in the Ainsworth Β series, b u t with a special beam and double air dampers. T h e beam deflection is shown on the re corder. T h e 11-inch chart covers the range from —5 to + 1 0 S mg. and can be read to ± 0 . 1 mg. T h e capacity of the balance is 200 grams. U p to this a m o u n t can be weighed on t h e p a n or suspended under the pan. F o r suspending samples u n d e r the balance, there is a hole u n d e r the left pan, and a hook on the underside of the pan. To suspend a sample above the bal ance, a special support and counter weight are furnished. I n use, t h e s u p p o r t replaces the left-hand pan and hangar assembly. I t extends u p through a hole in the t o p of the bal ance case and s u p p o r t s an V 8 - i n c h socket. Various sample s u p p o r t s (not furnished) can be inserted in the socket above the case. W h e n using Vg-inch diameter q u a r t z rod, 25 grams in addition to the rod can be supported above the t o p of the balance case. An extensiometer micrometer linear transducer is installed in the balance, with its probe attached to t h e beam. Two halves of the transducer form a bridge circuit with the slide-wire wind ing in t h e recorder. Any unbalance in the bridge circuit gives a signal which is amplified to operate the recorder and so rebalance the bridge. Only t h e linear range of t h e transducer is used, and it is matched to t h e slide-wire to give over-all linear response. This sys tem is not affected by variations in line voltage, tube characteristics, t e m p e r a ture, air pressure, or length of run, nor by nearly magnetic fields or materials,
INSTRUMENTATION or residual magnetism in the system. T h e recorder is standardized continuously without batteries, and no recalibration is required when tubes are replaced. Positive or negative increments of weight are t h u s continuously recorded. Whenever the recorder approaches either edge of the chart, weights are automatically added or subtracted, b y a cam and motor assembly under the balance floor, in 100-mg. increments. This moves t h e beam and recorder pen to the other end of their range. A warning light on the front of t h e balance indicates when such changes occur. T h e switch weights total 4 grams ; t h e equivalent of 40 chart widths and each weight or any combination of weights is accurate within 1/1000 of a chart width. F o r a load u p to 200 grams, any 4-gram change is handled automatically without alteration.
Beta reference source set
C A L I B R A T E D BETA REFERENCE SOURCES Five reference sources (Carbon-14, Cobalt-60, Thallium-204, Bismuth-210, Protoactinium-234 — plus spare mounts and copper planchets), with maximum energies from 0.155 to 2.32 Mev cover the energy spectrum range of most beta emitting radioisotopes. Ideal for use as check sources for testing counting equipment or as calibrated sources for determining millicurie strength of unknown samples having higher energy betas. Accuracy of calibration estimated to be within 10%. Sources contain between .01 and 1.0 microcuries. C-14 and H-3 standard reference source compounds also available.
Automatic Arrestment and Release
Technical bulletin with complete source information and specifications available on request.
new england nuclear corp. ® 575 ALBANY STREET,
BOSTON 18.
SALES REPS: Atomic Associates, Inc., Packard Instrument Sales Corp., Radionics, Ltd., ( M o n t r e a l ] . For further information, circle number 50 A-1 on Readers' Service Card, page 69 A
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ANALYTICAL
CHEMISTRY
Automatic beam arrestment and release occurs a t one to four times per hour, or not a t all, if desired, in order to correct for beam misalignment as a consequence of environmental vibration. Figure 2 shows the rear of t h e recorder unit, with the pen-raising lever at the extreme u p p e r left and the limit switches on the slide-wire d r u m which actuate the weight-adding or weightremoving mechanism. Figure 3 shows the arrestment motor, the sequencing of which is controlled by inserting pins in t h e timer wheel. In our humble opinion this recording balance represents the ideal a p proach. I t is a p p a r e n t t h a t no i m p o r t a n t aspect of classical balance design and construction has been overlooked. I t seems to us t h a t it is extremely imp o r t a n t t h a t a well established and respected balance manufacturer has u n dertaken this task. T h e average engineer or electronics expert would have no hesitation in tackling the problem of weight recording, b u t it is astonishing how few of t h e m have p r o p e r respect for the finer points of precise weighing. This is something which comes n a t urally to the professional analyst. I n particular, the automatic and periodic beam arrestment in the Ainsworth balance is a recognition of one of t h e fine points in balance operation. We like to think t h a t although Duval's famous thermogravimetric techniques provide the principal urge for recording balances, there will be m a n y unsuspected applications. This is p a r t of our ingrained prejudice concerning new instruments, b u t progress in science is based upon two requirements—new concepts a n d new tools.
