A NEW LEEDS & NORTHRUP COMPANY PUBLICATION

ELECTROMETRIC METHODS AND APPARATUS

FOR DETERMINING

HYDROGEN ION CONCENTRATIONS

CONTENTS

General Considerations-The Working Formulas-Electrometric Methods Applicable to Hydrogen Ion Measurements-Methods Employing the Potentiometer Principle-Practical Considerations in Applying Working Formulas-Applications of the Gas Chain to Titration Analysis Industrial Applications of Gas Chain Methods-Bibliography -Price List.

This new publication, Catalogue S75, devotes twenty-four pages to a disucssion in simple terms of the general questions pertaining to hydrogen ion concentrations and their measurement by electrometric methods. It explains PH, the "hydrogen ion exponent," its relation to hydrogen ion concentration, and the method for converting one to the other. It shows how the working formulas are obtained from Nernst's equation, and what precautions to observe in applying them. There is a section dealing with the different methods by which gas chain voltages may be measured without polarizing the source, and the advantages or limitations of each. A selected bibliography gives references to many original articles dealing with various chemical and biological problems to which gas chain methods have been applied. A price list of individual instruments and assembled outfits affords a wide choice, from which an equipment, suited to the particular needs of the user, may be selected.

If, in asking for your copy of Catalogue S75, you will tell us about the kind of work in which you are especially interested, it will enable us in the future to send you those of our publications which will prove valuable to you.

LEEDS & NORTHRUP COMPANY

ELECTRICAL MEASURING INSTRUMENTS

4901 STENTON AVENUE

PHILADELPHIA, PA.

For use with potentiometers, electrometers, and ballistic galvano meters, or wherever else a precision standard of electromotive force is needed.

Negligible Temperature Coefficient.
Highly Constant E. M. F.

Contents hermetically sealed in glass so that lowering of electromotive force due to evaporation is impossible.

Mounted in moulded box, or unmounted.

My comparison certificate accompanies each cell without charge.
Bureau of Standards certificate extra.

On November 13, 1916, three normal cadmium cells made by me were certified by the Bureau of Standards as differing from their group of reference cells by less than one part in one hundred thousand, all three having the same value.

On March 30 1920, after the lapse of three years and four months, the same three cells were again compared by the Bureau of Standards. The maximum difference among the three was less than one part per hundred thousand, and the maximum difference from their certified value of 1916, was less than one part per hundred thousand.

In other words, these cells showed a degree of constancy to all intents equal to that considered most highly satisfactory, if not remarkable, in the very best type of precision resistance standards. (see Bul. Bur. of Stand. Vol. 5, No. 3. p. 427.)

The cells in question were in nowise special. They were made of the materials regularly prepared by me, and were set up with no greater care than that constantly employed in the making of my standards.

Marion Eppley,

(A.M., Ph.D.)

Physico-Chemical Apparatus.

NEWPORT, R. I.

Constant-Temperature Apparatus

Dependable for Long, Continuous and Unattended Operation

FREAS OVEN TYPE R No. 100

Size of oven inside, 12"x12"x12". Temperature range, from room to 175°C.

Regulation, Freas Metallic thermo-regulator.

Construction, heavy asbestos tran-
site with cast aluminum frames
and insulated lining.
Operation, simply attach to lamp
socket.

Furnished with Special Ther-
mometer, ranging to 200°C.

Constant within one degree over
long periods.
SIMPLICITY or operation, ease of regulation, constancy and
general dependability are the reasons why FRÉAS Ovens have
been adopted by the most important laboratories of the U. S.
Government, the leading educational, scientific institutions and
the most progressive manufacturing plants in the country.
FREAS Ovens are made in several sizes and types. They are ap-
proved by the National Board of Fire Underwriters. They are
strongly constructed and reliable to the utmost detail. They may
be left in operation, unattended, for months at a time if required.
For Sale by All Dealers in Dependable Laboratory Apparatus

Sole Patentees and Manufacturers

8 Johnson
Street

The Thermo Electric Instrument Co., Newark, N. J., U. S. A.

See our exhibit at the Sixth National Exposition of Chemical Industries
Grand Central Palace, New York, Week of September 20th

A NEW

BOILING POINT APPARATUS

DESIGNED BY DR. F. G. COTTRELL

Director of the U. S. Bureau of Mines

and

MODIFIED BY PROF. EDWARD W. WASHBURN
of the University of Illinois

No. 10384

ADVANTAGES OVER OTHER TYPES

1. Provides perfect equilibrium between liquid and vapor phases

2. Enables the exact determination of the temperature of equilibrium to be made when both phases are under same external pressure.

3. Prevents superheating.

4. Reduces to a minimum variations due to size of flame, drafts of air, height of liquid, etc. 5. Insures a constancy of the mercury column ten times as great as in other methods.

6. Permits the accurate determination of molecular weights by the ebullioscopic method.
No. 10384. MOLECULAR WEIGHT DETERMINATION APPARATUS, Washburn-Cottrell,
as illustrated above, without Beckmann Thermometer.

For complete description of the apparatus and method of use, see the Journal of
the American Chemical Society, Vol. XLI, No. 5, for May, 1919, pages 721-741.

CENTRAL SCIENTIFIC COMPANY

460 East Ohio Street

$30.00

CHICAGO, U. S. A.