v a c u u m . One of these elements can be displaced w i t h equal precision in a direction rectangular to t h a t oi the axis of the bench. The accelerating voltage employed can be twice as high as in the case of the conventional design. The operational v a c u u m is of the order of 10 -5 ram. Hg, The single flat-shaped guide rail n o r m a l l y provided is replaced b y 4 r o u n d driving shafts.
So~maire : U n n o u v e a u bane d'optique 61ectronique est ddcrit.
Abstract No. and References
Article by
E. Bas Hdv. Phys. Acta 25, 15.6.1953 438-439
150/II
Polythene Windows for Vacuum Systems See A b s t r a c t No. 1 8 2 / I I I
Electrode Contamination in Electron Optical Systems
151/If
See A b s t r a c t No. : 196/I
0
Large Bent Crystal Vacuum X-Ray Spectrograph Swede.~*. An i n s t r u m e n t w i t h high resolving power for small intensities is described, designed for use in high vacuum.
The angular range covered is 35-80 °, and the range of w a v e l e n g t h covered is 3,500-19,600 X U .
( B.S. I . R . A . Bulletin) ,So~tm~aire : D6tails d ' u n spectrographe "~ r a y o n s - X sous vide, h large crystal courb6. A Vacuum Microbalance for Measuring Sorption in Dielectrics United I~ingdom. F o r the m e a s u r e m e n t of the rate of sorption of water v a p o u r b y non-polar dielectrics a
152/II Paper by A. E. Sandstroem
Ark. Fys., 4, 1952 517-534
153/II
microbalance w a s required w i t h a sensitivity of 1 in 10% The balance had to be suitable for operation in v a c u u m or at low pressures of a v a p o u r and h a d to w i t h s t a n d sudden pressure changes. An i n s t r u m e n t developed for the p u r p o s e is described in this article and is based on a design b y Pettersson. The balance b e a m was r h o m b i e in shape, constructed f r o m 0.4 ram. hard-glass fibres w i t h a tie b a r along t h e s h o r t diagonal. The cross b a r of 1 m m . diameter was joined to the centre of the tie bar. A m i r r o r was fitted to the cross bar. The b e a m was suspended b y 2 glass fibres d r a w n out to 6/x diameter at their b o t t o m ends (which were joined to the cross bar) from an adjustable s u p p o r t fitted to the top of the balance case. A fused q u a r t z torsion fibre, cemented to the mid-point of the beam, 12/z in diameter, was joined to a steel torsion drive outside the case and provided the m e a n s of m e a s u r i n g the change in weight of the specimen. The counter poise weight at one end of the b e a m w a s free to fall a limited distance. A projection microscope s y s t e m w a s u s e d t o indicate the position of the beam. The operating conditions of the balance are given in the table reproduced below. The case housing the i n s t r u m e n t was inserted in a t h e r m o s t a t i c a l l y controlled oven and could be evacuated b y m e a n s of a m e r c u r y diffusion p u m p to a pressure below 10 -4 m m . Itg. The balance was calibrated at the fixed load of O.1 g. Details of the calibration m e t h o d are given. The balance indicated reliably a change of weight of 0.02/xg,
Operating Conditions of the Balance Period of Swing Range of Torsion Fibre Sensitivity of Torsion Fibre Sensitivity of Balance Screen Sensiti~dty
0
10 sec 30O /~g
so/~g
2 x 10' radians/g 50 mm//*g
Article by A. G. Day
J. Sci. Instrum. SomJnaire : U n mod61e de micro-balance sous vide c o n s t i t u a n t une am61ioration de Ia balance conventionnell e k ressorts h boudin en q u a r t z fondu est d6crit.
30, August 1953 260-263
A Needle Valve-Type of Variable Gas Leak for Mass Spectrometers See A b s t r a c t No. : 164/II
154/II
A Vibrating Variable Gas Leak See A b s t r a c t No. : 194/I
155/II
A Double-Replica Method Using Carbon Layers Germany. The m e t a l surface to be investigated is covered w i t h a layer of e v a p o r a t e d silver at least 5 /z in
156/11
thickness. This layer is easily r e m o v e d from the surface and is t h e n covered w i t h a t h i n layer of silica, or better, carbon. The silver is dissolved in 40°,/0 nitric acid and the positive c a r b o n replica transferred to the specimen carrier of the electron microscope.
Article by V. C. Dalit~z & J. A. Sehuchmann
(Science Abstracts) Sommaire : Une technique d ' u n e r6plique d ' u n sp6cimen c o m p o r t a n t l'emploi de film de carbone est d6crite.