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.
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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.
