Announcing the New(||)EA System for ELECTROPHORESIS
REPORT
EA-4 Power Control Supply Designed especially f o r electropho resis. Continuously variable voltage Ο to 500 V. Stable: Supplies constant volt age. (Ripple less than ± 0 . 1 % . Unit regulates to ± 0.1%.) Also can supply constant current over entire range. No v a r i a n c e in mA w i t h c h a n g e in l o a d ± 90%. Double scale meter shows V and mA. Exclusive built-in t i m e r w i t h automatic shut-off. Four chambers — s i m u l t a n e o u s operation (7 tests per c h a m b e r ) . Constant c u r r e n t c o n t r o l over entire electrophoretic range.
EA-1 Electrophoresis Chamber High impact polystyrene; water cooling jacket. Domed see-through lid. Safety interlock. Platinum electrodes run en tire chamber length. Polarity reversing s w i t c h . Simple, accurate m e t h o d of attaching sample strip with flexible holders in integral p a r t of c h a m b e r unit. This system offers features and advan tages never before f o u n d in electro phoresis equipment. The design is su perb—and the system was precision built by scientists expressly for scien tists. Our free brochure will give you a full description complete with addi tional pictures.
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Carl Schleicher & Schuell Co. Keene, New Hampshire—Dept. AC-268 Please send free brochure on new S&S/EA System for Electrophoresis NameCompany. Address_ City-Zip#_
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STOCKED BY: Van Waters & Rogers, Inc. Will Scientific. Inc. · E. H. Sargent & Co. Circle No. 185 on Readers' Service Card 32 A
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ANALYTICAL CHEMISTRY
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T h e range of problems which can be investigated has been greatly extended as a result of the development of modern physico-chemical methods of analysis, which are sufficiently sensitive to give reasonably accurate results using samples of only a few milligrams. A comprehensive survey of the subject would be beyond the scope of the present article; instead selected examples have been t a k e n to illust r a t e the basic principles involved. W e will start by considering some problems involving systematic analysis, in which the techniques t h a t have proved to be of most general application are those of emission spectrography, atomic absorption, X - r a y diffraction, and X - r a y fluorescence analysis. One problem which is of particular interest to archaeologists is the sources of metallic ores used for the production of ancient metal objects. Some investigators have thought t h a t t h e sources of ancient ores could be traced by finding a correlation between the t r a c e impurities found in ancient metals and those present in the various geographical deposits. There are, however, two difficulties inherent in this proposal. First, m a n y ore deposits worked in ancient times m a y be exhausted so t h a t ancient ore material will not be available for comparison, and, second, m a n y ancient metal objects —particularly from later civilizations—were m a d e by remelting scrap metal t h a t m a y have come from a variety of original sources. However, in special cases such correlation between ore and metal m a y be possible. For example Otto and W i t t e r (7) carried out a systematic spectrographic analysis of prehistoric copper and bronze objects from Central Europe, and were able t o demonstrate the presence of a p preciable proportions (in the range 0.3 to 2 per cent) of arsenic, a n t i mony, bismuth, and silver, thus indicating the use of the tetrahedrite ore of the German deposits which characteristically contains all these impurities. A similar a t t e m p t to differentiate the geographical sources of the metal of prehistoric copper and bronze objects over a m u c h wider area in E u r o p e has been m a d e by Junghans, Sangmeister,
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The new range of EMI photomultipliers with "SUPER" S-ll photocathodes will enhance your project performance. High quantum efficiency, (23/24%) high gain at relatively low overall voltage, and low dark current at the rated overall sensitivity are typical of these types. They maintain the EMI standard of excellent gain stability and linearity. The narrow spread in characteristics makes these types ideal for systems or for multiple installations. The table below gives the typical values for the significant parameters. Amps/ Volts/ Lumen Overall
Type No.
lia.
Anode Dark Current Nanoamps
2" 3"
9656R 9708R
50 50
1250
2 5
3.5"
9531R
200
1300
25
4"
9732R
50
1250
10
5"
9709R
50
1350
15
1150
Note that the anode dark current is given for the overall voltage at the specified overall sensitivity. The maximum overall sensitivity is 10 times the values given above. Each Tube is individually calibrated and data is supplied with the tube. Send for our new 64 page catalog giving data and technical information on the complete range of EMI photomultipliers.
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G E N C O M DIVISION 80 Express St., Plainview, L.I., N.Y. 516-433-5900 Circle No. 86 on Readers' Service Card
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