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OHAUS TRIPLE BEAM BALANCE Model 750-S
$19.15
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FOR WIDEST SELECTION, GREATEST CAPACITY SPECIFY OHAUS. THERE IS A MODEL TO FIT YOUR EVERY NEED.
NEW BOX END BEAM High strength, die cast aluminum alloy, with ends cross braced. SLIDING POISE with center indicating panel, insures rapid correct readings. Eliminates secondary beam oscillations.
ANGLE-VIEW BEAMS stainless steel relief etched graduations for easy reading.
END READING DEVICE pointed beam registers' against graduated dial eliminating parallax error.
AHACHMENT WEIGHTS extend capacity to 2610 grams with this handy set. Ust Price $5.00 WRITE FOR FREE BROCHUBE
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lOSO COMMERCE AVE. UNION. NEW JERSEY Circle No. 143 on Readers' Service Card
26 A
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ANALYTICAL CHEMISTRY
R O T A T I N G PLATE ELECTRODE
processes with heterogeneous kinetics on electrodes made from different metals. The rotating plate electrodes enable to some extent the quantitative investigation of the dependence of the flow density on the intensity of stirring and determination of the reaction order. The rotating plate electrode can be used to investigate kinetics of processes which occur within a solution, when the reaction products take part in an electrode process. -With the help of such electrodes, two simultaneous reactions occurring at the same potential can be separated when the velocity of one process can be determined by diffusion and consequently it depends on the stirring while the velocity of the other process is independent of the intensity of stirring. The rotating electrode, as distinguished from the mercury drop electrode, permits the investigation of reduction, as well as oxidation processes of different metals and within large potential limits. 3. Analytical determination of concentrations of electrochemically active substances. A correction for the charging current does not have to be used. When the value of the diffusion coefficient, D, is known, the previously used calibration of the measuring arrangement (apparatus) with the help of a standardized solution of known concentration is superfluous. 4. Investigation of t h e kinetics of solut i o n s of m e t a l s . W h e n an especially int e n s e m i x i n g is n e e d e d , o n e uses i n s t e a d of a plate electrode, a r o t a t i n g r - s h a p e d electrode a n d works under t h e c o n d i t i o n s of t u r b u l e n t flow. T h e a r r a n g e m e n t consists o f a high f r e q u e n c y electric m o t o r with a r o t a t i n g electrode, an electrochemical cell, a high f r e q u e n c y generator, a s i m u l t a n e o u s current m o t o r w i t h a n adjustable rheostat, a n d a»strobotachometer in order t o measure t h e rotation velocity of t h e electrode. T h e electrochemical measurements
are m a d e w i t h t h e help of a s t a n d a r d s e t u p f o r t h e m e a s u r e m e n t of t h e c u r r e n t intensity a n d of t h e p o t e n t i a l . MASS
SPECTROMETER.
In
designing
their m a s s s p e c t r o m e t e r for t h e determ i n a t i o n of free radicals, particular a t t e n t i o n was paid t o o v e r c o m i n g t h e difficulty of t h e f o r m a t i o n of ionized f r a g m e n t s by t h e electron b o m b a r d m e n t of m o l e c u l e s . These f r a g m e n t s are often identical in mass w i t h t h e free radicals. This probl e m w a s overcome by u s i n g t h e p h e n o m enon of charge exchange t o ionize t h e radicals in t h e presence of other substances. By proper selection of b o m b a r d i n g ions, it is possible t o o b t a i n a s p e c t r u m of molecules present which is considerably s t r i p p e d of f r a g m e n t ions a n d therefore does not s u p e r i m p o s e on t h e s p e c t r u m of t h e radicals. T h e device also provides for a possible ionization of radicals by t h e orthodox m e t h o d — f o r e x a m p l e , b y electrons w i t h reduced energy. In this case t h e m e t h o d of " q u a s i - m o n o c h r o n i a t i z a t i o n " of t h e electron b e a m is e m p l o y e d , which has been i m p r o v e d in t h a t t h e " c u t t i n g o u t " of t h e m o n o e n e r g e t i c group of electrons is e f f e c t e d by periodic m o d u l a t i o n of voltage on t h e c a t h o d e grid of t h e ion source. This m a k e s it possible t o improve t h e sensitivity of recording t h e ion current by u s i n g a resonance amplifier a d j u s t e d to the modulation frequency. To improve t h e sensitivity, an ionization c h a m b e r provided w i t h preconversion of ion current into electronic o n e was used for t h e first t i m e in mass spect r o m e t r y w i t h t h e object of i n t e n s i f y i n g t h e ion c u r r e n t . T h e general diagram of t h e device is given in t h e figure. T h e molecular b e a m of t h e m i x t u r e analyzed passes f r o m t h e reactor, R, t h r o u g h t h e d i a p h r a g m s , 1 a n d . 2, into t h e ion source, 3, where ionization is e f f e c t e d either by electrons e m i t t e d by t h e c a t h o d e , 4, or by ions o b t a i n e d in t h e
