Bibliography

Paul Walden. Elektrochemie der nichtwässerigen Lösungen. (Handbuch der angewandten Physikalischen Chemie, edited by G. Bredig, Vol. 13). Leipzig: Johann Ambrosius Barth. 1923. 11, 515 pp. and 3 figures in the text.

P. Walden. Electrochemistry of Non-Aqueous Solutions.

After a long interval, another volume has appeared of the well-known and truly monumental work on applied physical chemistry edited by Bredig. In this volume Academician P. I. Walden presents the electrochemistry of non-aqueous solutions. It would hardly have been possible to name anyone more competent for carrying out this task. For, beginning in 1887 with measurements of the electrical conductivity of aqueous solutions of simple and double salts and with the application of this method to the determination of the molecular weight and atomicity of acids and bases (the Ostwald–Walden rule), P. I. Walden himself studied (1890–1896) the electrical conductivity of about 200 acids in order to determine Ostwald’s “affinity constant” and to establish the relation between it and the structure of three acids. From 1899 onward, guided by Arrhenius’s theory of electrolytic dissociation, he investigated non-aqueous solutions, was the first to introduce new inorganic solvents (e.g., \(SO_2\), \(SOCl_2\), \(SO_2Cl_2\), \(POCl_3\)), as well as a number of organic ones; he was the first to study more than 50 non-aqueous solvents with respect to their ionizing power, using the same electrolyte, \(N(C_2H_5)_4J\), and established, in accordance with the Thomson–Nernst rule, the parallelism between it and the dielectric constant of these solvents; he discovered the relation between the molecular electrical conductivity \(\lambda_\infty\) at infinite dilution and the internal friction \(\mu_\infty\) of the solvent: \(\lambda_\infty \cdot \mu_\infty = const.\) (1906, 1911, 1913).

Only a scholar who had himself devoted a large part of his life’s work to this problem and who, moreover, possessed a special literary talent could rework the entire immensely expanded field of the electrochemistry of non-aqueous solutions and present it in such a clear, simple, and convenient form for orientation.

It should be recognized as a special merit of the author that he vividly brings to the fore all those problems that still remain unsolved and await further scientific treatment: the processes of solvation, association

and polymerization. P. I. Walden takes an objectively restrained attitude toward the latest theories of Ghosh and his predecessors as applied to nonaqueous solutions.

We cannot, of course, give a detailed abstract of the contents of this voluminous work. We shall indicate only those conclusions at which the author himself arrives:

1. Water is by no means typical of the nonaqueous solvents and ionizing media that have been studied (more than 100).

2. The study of nonaqueous solutions has again awakened interest in “concentrated” solutions.

3. In the latter, chemical factors play a decisive role (association between the dissolved substance and the solvent—solvation; depolymerization of dissolved molecules; splitting of salt-like molecules into components: acid and base (solvolysis, and many others)).

4. The role of physical factors in the processes of dissolution is likewise beyond doubt (electrostatic attraction, and many others).

5. There are no indifferent, isolating solvents either in the electrochemical or in the chemical sense of the word.

6. Among the physical properties, the dielectric constant is the most characteristic.

7. In the usual sense of the word, conductors and electrolytes are not only dissolved salts, but also, for example, organic halogen compounds, especially together with aromatic radicals, when appropriate solvents are used.

8. The electrolytic theory of solutions of Svante Arrhenius, which qualitatively and quantitatively explains phenomena in dilute solutions, still remains the best guide in the field of nonaqueous solvents as well. In this latter case, the presence of a chemical factor was already noted by Arrhenius himself.

9. By the very nature of the problem (the abundance of solvents and of conditions of dissolution), work in this field has proceeded more in breadth than in depth.

10. For a long time yet, the electrochemistry of nonaqueous solutions will represent an untrodden field of work for scientific research.

At the present time it seems self-evident that chemical and physical research are closely connected with one another. One involuntarily recalls, in the distant historical perspective, that in the 1860s and 1870s of the last century, at the height of the syntheses of organic chemistry, the application of physical methods in chemical investigations was considered the occupation of “theorists.”

True, physics, having found the gas laws, created the foundations of molecular theory; nevertheless, it remains a fact that, although the name of Gay-Lussac enjoyed universal respect, the name of Avogadro had to be resurrected from oblivion some 50 years later.

Among broad circles of chemists, awareness of the close connection existing between physics and chemistry penetrated only thanks to the theory of electrolytic dissociation; and the role that Gay-Lussac and Avogadro played in the development of the doctrine of the gaseous state was played by Van ’t Hoff and Arrhenius in the development of the doctrine of liquids.

At the present time we are living through a third epoch of the fruitful influence of physics upon chemistry: penetration into the structure of the solid state of matter with the aid of the doctrine of radiation.

Reading the work of P. I. Walden not only enriches us with factual knowledge of what has been done and created, but also awakens our thought, showing how many unsolved problems stand before the inquisitive mind of man.

M. Bloch.