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

A.H.T. CO. SPECIFICATION

SERFASS CONDUCTANCE BRIDGE DIRECT READING M H O - O H M MODEL

3965.

CONDUCTANCE BRIDGE, Serfass, Direct Reading Mho-Ohm Model, A.H.T. Co. Specifica­tion. Portable and self-contained, with cell constant compensator, sensitivity control, frequency selector switch, and modified circuit providing absolute readings of specific conductance in micro mhos per centimeter, or in ohms resistance by merely shifting a twelve-position multiplier switch; as suggested by Dr. Earl J. Serfass, Department of Chemistry, Lehigh University. In use, the necessity of calculating reciprocals, making cell constant corrections, etc., has been eliminated, making the Mho Bridge especially suitable for making conductometric titrations and analyses.

Range is from one to one million micro mhos per centimeter specific conductance, or from 1 ohm to 1 megohm measured resistance in six steps on the multiplier switch. Accuracy is within ± 1 % of readings, except at extreme ends of overlapping ranges, which are used only for location of initial balance point of bridge.

The dial has linear calibrations from 0.5 to 10.5 in 0.1 divisions which provide uniform accuracy for all readings within range of 1.0 to 10.0, i.e., avoiding inherent inaccuracies in the potentiometer windings at the extreme ends. The cell constant compensator, with pointer knob, has range from 0.90 to 1.10 in 0.005 subdivisions. The bridge source selector switch provides an a.c. input of either 1,000 cycles per second with less than 5 % distor­tion, or line frequency of 50 or 60 cycles. The sensitivity control knob, in the circuit with the 6E5 cathode ray tube, permits continuous adjustment of the sensitivity on both resistance and conductance measurements; low sensitivity setting facilitates location of proper multiplier position and

balance point. Use of a 6SL7 twin triode electronic tube provides two-stage amplification of the bridge output voltage.

Dipping type Conductivity Cell 3995, with cell con­stant of approximately 1.0 reciprocal centimeter, is sug­gested for use with the Serfass Mho Bridge for general use where ample volumes of sample are available. The cell is suitable for most solutions excepting distilled water, steam condensate, or samples with low conductivity, for which 3996 Conductivity Cell, with cell constant of approximately 0.1 reciprocal centimeter is suggested. For small samples of medium or high conductivity we offer 3997 Micro Dipping Type Conductivity Cell, with cell constant of approximately 1.0 reciprocal centimeter, which can be used in volumes as small as 5 ml. When using a cell with cell constant beyond the range of the "cell constant compensator," the compensator knob is set to 1.0 and the main dial reading is merely multiplied by the cell constant.

The Serfass Mho Bridge is convenient for use in making accurate conductometric titration measurements as it eliminates the need for calculation of reciprocals. {Details of a recommended assembly sent upon request.)

3965. Conductance Bridge, Serfass, Direct Reading Mho-Ohm Model, A.H.T. Co. Specification, as above described, with 5 ft. connecting cord and plug and directions for use, but without conductivity cell. For use on 115 volts, 50 or 60 cycles, a.c. only 150.00 Net weight 11 lbs., 14 oz. Shipping weight 15 lbs. Code Word Eckry

3995. Conductivity Cell, Dipping Type, for solutions of high or medium conductivity, cell constant approx. 1.0 reciprocal centimeter. . 29.00 3996. Ditto, but for solutions of low conductivity, cell constant approx. 0.1 reciprocal centimeter 29.00 3997. Ditto, Micro, for solutions of high or medium conductivity, cell constant approx. 1.0 reciprocal centimeter 29.00

ARTHUR H. THOMAS COMPANY RETAIL—WHOLESALE—EXPORT

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

Cable Address "Balance," Philadelphia