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 discussion 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.

DIFCO

Dehydrated Culture Media

ACCURACY is the goal of all work in bacteriology, as well as in
chemistry. It is better served when all bacteriologists work
with uniform culture media, standardized to a high degree of
uniformity, as in the use of "Difco" Culture Media, Dehy-
drated. Uniformity of cultural factors is assured, either for
the same worker at different times, or for different workers
at the same time.

SPEED is greatly desired in bacteriological procedure and no ad-
vance in this respect has been made for many years that com-
pares with the use of "Difco" Culture Media, Dehydrated.
The saving in time, as contrasted with the old methods, is easily
demonstrated, and the difference is incredible.

CONVENIENCE becomes a prime consideration when accuracy

and speed are at stake. The convenience of "Difco" Culture
Media, Dehydrated, can be appreciated only by actual trial.
Think of having a dozen different formulas in convenient
packages on your shelves, needing only one weighing and the
addition of water to obtain a medium ready to sterilize.

ECONOMY is a consideration when quality has been satisfied.
The use of "Difco" Culture Media, Dehydrated, assures
economy, not only thru the factors of Accuracy, Speed, and
Convenience, but by actual comparison of costs, based on
materials, labor and time.

More than a dozen standard formulae, all carried in stock by
the principal dealers in scientific supplies. Descriptive bulle-
tins upon request.

Your inquiries are solicited

DIGESTIVE FERMENTS COMPANY

DETROIT, MICHIGAN, U. S. A.

Immediate Delivery. Write for our booklet on Blood Chemistry

C. M. SORENSEN CO., Inc., Dept. K

GENERAL DISTRIBUTORS

177 East 87th Street

NEW YORK

Announcing

ELLIOTT-ACREE HYDROGEN ION APPARATUS

EQUIPPED WITH PH TYPE NORTHRUP PYROVOLTER

Pyrolectric Instrument Co. is pleased to announce that after exhaustive tests and close collaboration with the Grahame Chemical Co., a small, rugged, reliable potentiometer, operating on the well-known Pyrovolter principle, has been developed for use with the Elliott-Acree apparatus (described at St. Louis meeting, American Chemical Society).

The complete outfit, or any part, is now offered by both Companies. It is of especial value where simplicity and convenience are appreciated in determining hydrogen ion concentrations. The apparatus is less expensive, smaller, simpler, and more readily portable than any other at present available.

The potentiometer (Pyrovolter) is of the double pivot, permanent magnet type, offering indications by deflections. No standard cell is required. There are three tapping keys to prevent polarization of electrodes. The scale is calibrated in two ranges, 0-200 millivolts and 0-500 millivolts, corresponding to pH values 2 to 9 and 1.5 to 15. The accuracy is guaranteed to be within 0.2% of full scale at any scale division. This accuracy for both scales assures precise measurements over the entire ranges found in practice.

Ask us for Bulletin BS-14, describing the complete apparatus

PYROLECTRIC

INSTRUMENT CO.

636-640 EAST STATE STREET

TRENTON, N. J.

GRAHAME CHEMICAL CO.

100 ROCKINGHAM STREET ROCHESTER, N. Y.

BOOTH 288 at Sixth Exposition of Chemical Industries