Humboldt State University ® Department of Chemistry

Robert A. Paselk Scientific Instrument Museum

 
From: Braun Corporation, Catalog No. 34, Laboratory Instruments, Apparatus and Supplies, Braun Corporation (1934) pp. 437 & 440.
 
Courtesy of VWR Scientific Products Corporation
 

 

HYDROGEN-ION DETERMINATION

 

ELECTROMETRIC

 
THE Electrometric Method is the most accurate of the methods employed for the determination of Hydrogen Ion Concentration and the accepted method for research and laboratory work necessitating pH measurements accurate to 0.1 to 0.001 pH and for checking and standardizing the Calorimetric Method, except in those cases where the presence of certain classes of substances in the solution interferes with the measurement of the potential of the unknown half-cell.
 
The Electrometric Method for determining the Hydrogen Ion Concentration, or pH value, of a solution consists essentially in measuring the difference in potential between two special electrodes in contact with, the solution by means of a null potentiometer, the electrodes and solution comprising an electric cell, called a concentration cell or chain, in which one electrode develops a potential according to the Hydrogen Ion Concentration of the solution, while the other electrode has a constant, definite potential independent of the Hydrogen Ion Concentration of the solution. The value is obtained by measuring the potential of the combination and deducting the potential of the known electrode or standard half-cell from that of the whole. The electrodes commonly used are the Hydrogen Electrode, the Quinhydrone Electrode and the Calomel Electrode. The usual combinations are the Hydrogen-Calomel Electrode and the Quinhydrone-Calomel Electrode Assemblies. It is essential in making the measurement that no current be drawn from the electrodes and this is accomplished at the balance point with the null potentiometer.
 
TECHNICAL REFERENCES
 
For detailed discussion of the theory and significance of Hydrogen Ion Concentration, Its measurements by means of electrometric or potentiometric methods, and its fields of application, reference should be made to the following publications:
The Determination of Hydrogen Ions, by W. Mansfield Clark. Williams & Wilkins Co., Baltimore. This is the classic work on this subject.
 
Hydrogen Ions, Their Determination and Importance in Pure and Industrial Chemistry, by H. T. S. Britton. D. Van Nostrand Co., New York.
 
Potentiometric Titrations, by I. M. Kolthoff and N. H. Furman. John Wiley & Sons, New York.
 
Hydrogen Ion Concentration, Its Significance for Biology and its Measurements, by L. Michaelis. Williams & Wilkins Co., New York.
 
The Measurement of Hydrogen Ion Concentration, by Julius Grant. Longmans, Green & Co., New York. A small practical book on both theory and practice for the worker.
 
Notes on Hydrogen Ion Measurements, Note Book No. 3, Leeds & Northrup Co. A 48 page booklet discussing the meaning of Hydrogen Ion Concentration and pH value, the technique of electrometric or potentiometric measurements, and the selection and preparation of electrodes. A copy will be supplied, without charge, upon request.

 

 
 
 
ELECTROMETRIC pH MEASUREMENT EQUIPMENT
 
Proper electrometric or potentiometric pH measurement assemblies and Instruments specially selected for research and development, general laboratory work, process control, and educational instruction are illustrated and described on the following pages. These Include high precision instruments for research, combinations of units for educational purposes, and rugged and compact instruments for Industrial laboratory use, with accuracy the dominating factor in the first, and simplicity and speed commensurate with moderate accuracy the dominating factors in the latter. The instruments listed have been found by years of experience to be particularly adapted to the uses for which they are recommended. The descriptions indicate the conditions for which each instrument or equipment is most suitable, and the accuracy it is capable of affording.
 
 
 
 
34304 HYDROGEN ION OUTFIT, Simplified Potentiometer, Leeds & Northrup - The simplified potentiometer Hydrogen Ion Outfit is an assembly made up of the No. 23215 Simplified Potentiometer unit and accessories, and is especially well suited for instruction and training in potentiometric titrations, pH measurements and oxidation-reduction determinations. It is also applicable and used for work within its limit of accuracy in Industrial laboratories, and even in some research.
 
The Simplified Potentiometer may be used for other work also in chemical and physical laboratories besides pH determinations. It is equally well suited, when used with other accessories, for instructional work in instrument checking and standardizing, thermocouple temperature measurements, etc. The Simplified Potentiometer has ranges of 0 to 16 millivolts, and 0 to 1.6 volts. The latter range is for pH measurements, and the balance position can be read to a limit of error of .01 pH.
 
The No. 34396 Pointer Type Galvanometer is sufficiently sensitive for pH measurements on ordinary types of solutions. For work on solutions with higher resistances, a more sensitive galvanometer should be used.
 
The assembly supplied includes the following apparatus:
Simplified Potentiometer No. 23215. Calomel Electrode Vessel No. 34438
Four Dial Resistance Box No. 23246. Single Contact Key No. 23250 (2 supplied)
Pointer Type Galvanometer No. 34396. 10,000 ohm Protective Resistance No. 34415
Eppley Standard Cell No. 19826. Double Pole, Double Throw Switch No. 34412
Hydrogen Electrode No. 34420.
 
Complete as listed, without dry cells, beaker, stand or clamps....................................Each 169.15


 

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Last modified 22 July 2000