18 A A N A L Y T I C A L C H E M I S T R Y

S E R F A S S E L E C T R O N RAY T I T R A T I O N

A S S E M B L Y FOR THE DETERMINATION OF ENDPOINTS IN GENERAL

OXIDATION-REDUCTION REACTIONS

ELECTRON RAY TITRATION ASSEMBLY, Serfass. The outfit operates directly from either a.c. or d.c. supply systems on a simple electronic circuit designed by Dr. Earl J. Serfass, of Lehigh University. See Industrial and Engineering Chemistry, Anal. Ed., Vol. 12, No. 9 {Sep­tember 15th, 1940), -p. 586. The amplified potential differences originat­ing between the electrode-solution interface are transmitted to the electron ray tube ("magic eye") which indicates endpoints instantane­ously by a change in the size of the wedge-shaped shadow which appears on the circular fluorescent target within the tube. The endpoint occurs when the largest per­manent change in shadow angle takes place per drop of t i trant added.

The control unit consists of a compact vacuum lube voltmeter with voltage regulator and connections for power supply, electron ray tube, electrodes and stirring motor. On the panel are dials for variation of sensitivity and control of the ray position and switches for connection with power supply and stirring motor and for control of the polarizing current. The electron ray tube is mounted in a separate housing with adjustable clamp for attach­ment to the vertical rod of a support stand for convenient observation of endpoints as indicated by the opening and closing of the "eye."

The outfit utilizes the self-polarizing platinum-tungsten electrode system and is suitable for use with platinum-nickel, calomel-platinum or polarized platinum-platinum electrode systems as in the Karl Fischer reagent procedure, but is not adapted for titrations requiring the glass electrode. 4937.

Particularly suitable for: General potentiometric titrations involving potassium dichromate, iodine, permanganate, eerie sulphate, ferrous sulphate, sodium thiosulphate and ferrocyanide. The direct determination of chromium and vanadium in steel. The determination of chromium in chrome tanned leather and in chrome tanning liquors. Limited applications to acid-base and precipitation titrations, but not adapted for pH determinations.

Advantages: Simplicity of operation. Turbidity and color do not affect accuracy. The usual delicate indicating meter isjreplaced by the electron ray tube which indicates continuously without the annoyance of key tapping. Line operation eliminates the inherent disadvantages of battery operation. A voltage regulator stabilizes the instrument against a.c. line fluctuations. Sensitivity is continuously variable, with full 100° shadow angle change in the "magic eye" with as little as 100 millivolts change in potential. The control unit supplies polarizing current when required for polarizing mono-metallic electrodes. The electrical unit is placed to one side of the titration stand and is therefore not subject to corrosion from the sample.

4937. Electron Ray Titration Assembly, Serfass, as above described, complete assembly as shown in illustration, consisting of control unit with electron ray tube in séparai» housing with adjustable clamp for'attachment to support rod, titration stand complete with base and swinging shelf of Coors porcelain, paired burettes, clamps, platinum and tungsten electrodes with holder, and variable speed stirring apparatus with motor for 115 volte, 60 cycles, single phase a.c. With detailed directions for use including step by step procedures for typical titrations and preparation of standard solutions 143.35

4937-F. Control Unit, Serfass, only, as included in above outfit, with electron ray tube in separate cylindrical housing with adjustable clamp for attachment to support rod. For 115 volts, 60 cycles, a.c 68.70 NOTE—Control Unit can be supplied for use on 220 volts a.c. and for 115 or 230 volts a.o./d.c. Prices on request.

More detailed information sent upon request.

ARTHUR H. THOMAS COMPANY RETAIL — WHOLESALE — EXPORT

LABORATORY APPARATUS AND REAGENTS WEST WASHINGTON SQUARE, PHILADELPHIA 5, PA., U. S. A.

Cable Address "Balance," Philadelphia