REPORT

on an overseas research trip

in the summer of 1910.

The immediate purpose of my overseas trip was the desire to acquaint myself with the method for studying the linear rate of crystallization of supercooled molten crystalline substances, developed by Prof. G. A. Tammann and his students in the laboratories of the universities of Yuriev and Göttingen.

In addition, intending to familiarize myself with the latest foreign literature on the question of the rate of crystallization under other conditions, in particular from saturated solutions during free evaporation, I planned to work in the Göttingen university library.

Finally, incidentally I intended to become acquainted with the organization of laboratory classes and lecture experiments in physics and chemistry, both in higher and in secondary schools—with this aim I intended to inspect, along the way, universities, institutes, Realschulen, and also those institutions which equip our laboratories.

Since the chief purpose of the trip was the intention to work in the Physico-Chemical Institute of Göttingen University, directed by Prof. G. A. Tammann, I consider it convenient to begin with a description both of the Institute itself and of the work in it.

The Physico-Chemical Institute is housed in a small two-story building, little adapted for physico-chemical work—this is explained by the fact that it was converted from a private building. The Institute was originally equipped by W. Nernst and is still now in the stage of equipment, which G. A. Tammann is continuing.

The basement consists of a materials room, four rooms for work in thermal analysis, where two Tammann electric furnaces are installed, supplied with current from the municipal network and provided with converters for transforming alternating current into direct current. Here also, in the basement, are the assistant’s office, a small photographic room, and a room for a dynamo that charges a small battery of accumulators and sets in motion

... a pump for Linde’s machine. The basement room is always lit by electricity, since daylight penetrates only weakly.

The lower floor is occupied by the following rooms: a small office of Prof. Tammann connected with his personal laboratory of tiny dimensions, adjoining which is the office of his closest assistant, Dr. Levenstein. Along the very middle of the lower floor, beginning from the vestibule, stretches a narrow, long, and dark corridor, dividing the rooms as follows: to the right, two rooms for doctoral students and higher-level offices; to the left, the mechanic’s office, the workshop, the library, a room for storing instruments, two rooms for work on crystallization and calorimetry, and, finally, the corridor ends in a small hall, a former lecture room, where apparatus for work at high pressures is housed. A small corridor connecting the lower floor and the basement leads into a lecture room for 100 people. To the right and left along the corridor are the room for the lecture assistant and a small optical laboratory. Without dwelling further on the external aspect of the Institute, I turn to the character of the teaching of physical chemistry at the Institute.

The theoretical instruction is chiefly in the hands of Prof. Tammann and partly of Prof. Coehn, as well as of the Privatdozenten.

Prof. Tammann gives the principal course in physical chemistry, lecturing on the following courses: equilibrium in homogeneous and heterogeneous media, a course in electrochemistry, and he conducts colloquia. The course is accompanied by demonstrations of tables, models, drawings, and experiments.

Since the exposition of equilibrium in heterogeneous media is one of the most difficult questions in physical chemistry, and its exposition is impossible without spatial representations, the lecture room must therefore be equipped with aids and models depicting the equilibrium of systems of dissolved substances. As an example I shall point to the model by Prof. Meyerhoffen (Räumliche Darstellung der Gleichgewichtsverhältnisse der Carnallits), tables with solubility curves, etc. There are very many such models here, since the students themselves are engaged in making them during their practicum.

One of the best measures for raising the scientific spirit and for acquainting students with the literature of the subject is the existence of a colloquium, which takes place weekly and lasts about 1–2 hours. The colloquium is devoted to the discussion of physicochemical works published chiefly in Z. für Physik.-Chemie. Each doctoral student working in the laboratory is obliged to give a report at least once during the semester. During the report there are debates, conducted by Prof. Tammann in collaboration with Prof. Coehn.

The practical study of physicochemical methods is in the hands of Prof. Tammann, Coehn, Sigmondy, and the assistants. There exists...

a compulsory practicum, comprising a series of problems in physical chemistry. These exercises are intended to acquaint beginners with experimentation. The problems are selected and divided by sections and consist of comparatively easy initial tasks: determination of the melting point; finding the density of solid and liquid substances; determination of molecular weight by the methods of Raoult, Dumas, and V. Meyer; determination of the rate of reaction; rate of crystallization; measurement of the electromotive force of an element; resistance of an electrolyte; rate of ion transport; rotation of the plane of polarization, etc. Optional courses exist in metallography, photochemistry with a practicum, the study of radioactivity, the study of colloidal substances, and ultramicroscopy. The last course, with the use of the new Cardiad microscope, is conducted by Prof. Siedentopf. The final stage in practical and theoretical acquaintance with physical chemistry is the independent investigation of a question proposed for doctoral work. As examples of questions being solved, I shall indicate several topics. Heat of neutralization of hydrofluoric acid. Solubility of solutes in gases at high pressures and various temperatures. Magnetic properties of ferric oxide. Optical properties of certain organic solvents at various temperatures. Investigation of the pair Ca + a series of metals: Fe, Ag, Cu, Al, Mg, etc.

Limiting myself to what has been set forth about the teaching of physical chemistry, I find it convenient to describe briefly the course of my work in the Institute.

My work in the laboratory was devoted to investigations of the rate of crystallization of supercooled molten crystalline substances (Schmelzen), and in particular I studied the influence of the bore of the tube on the linear rate of crystallization. The essence of the problem I was solving was as follows: by the work of Tammann and his school it had been established that the influence of the bore of the tube on the rate of crystallization is reflected in the character of the velocity curve; i.e., the velocity curves for tubes of different diameter, when one and the same substance crystallizes in them, intersect at a point lying close to the melting point. I intended to reduce the bore of the tube to very small dimensions and to make use of calibrated capillaries (proposed by G. A. Tammann) with a diameter of 0.05–0.06 mm, and to study the influence of reducing the bore on the rate of crystallization. A priori one may say that the influence should tend toward a decrease in crystallization, especially in substances with low heat capacity. According to Tammann’s theory, the rate of crystallization in supercooled molten substances is due to the fact that at the boundary layer separating the two phases a temperature difference is created, since at the moment of crystallization the temperature of the substance reaches the melting point—the rate of this process is determined by the temperature difference and, moreover, by the rate of cooling (the rate of dif-

heat dissipation). Since there is little substance in a capillary with an aperture of 0.05 mm, then, given its insignificant heat capacity, one may expect that in the boundary layer there will not arise that temperature difference which determines a certain rate of crystallization; and in any case the maximum of crystallization shifts toward the melting point and will be smaller than the maximum for the same substance crystallizing in a tube with a larger aperture. Moreover, the rate of crystallization, as is known, depends on impurities, and impurities lower the rate of crystallization; consequently, one may expect that impurities during crystallization in capillaries will have a more noticeable effect, since, with the small amount of substance placed in the capillary, the influence of purification will be noticeable.

Over the course of 2 months, with 10 hours of daily work, I succeeded in studying 2 substances: formanilide and diphenylamine. The third substance, guaiacol, was so difficult to purify that the curves of the rate of crystallization cannot be used in the calculation.

The chief reason—apart from the great number of readings needed to construct a curve—for the slowness of the work lies in the preparatory operations, which take up a very large amount of time. Purification of the preparation by recrystallization, often repeated four times; preparation and drying of the capillary—take several days.

The curves I obtained have not yet resolved the question of the influence of capillaries on the rate of crystallization, since, although a lowering was observed, it was insignificant, and the very course of the curve indicated that here the greater role is played by the small quantity of substance present in the capillary—the curve turned out to be consonant with the curve in a wide tube, only the point of constant crystallization shifted toward the melting point. Later, in my own laboratory, subjecting three other substances to study (phenyl dimethyl carbinol, calcium nitrate, and manganese nitrate), I obtained curves for capillaries that did not agree with the curves in wide tubes (diameter from 1.5–2.0 mm) and with greater decreases as the supercooling increased.

I turn to the second purpose of my trip. My work in the library of the University of Göttingen was very brief, since the principal works on crystallization I found in the library of G. A. Tammann and of the Institute. Only a few new sources, at my request, were ordered from other places (Leckhardt—Recherches expérimentales sur la vitesse de cristallisation des sels hydratés, Masius: Über die Absorption in Gemischen), but, unfortunately, they arrived somewhat late, and I had only to glance through them, since they were received 2 days before my departure.

Finally, the third purpose—acquaintance with other higher and secondary schools of Germany—remained almost unrealized. I only

I had occasion to inspect in Berlin the Physico-Chemical Institute, the laboratory of W. Nernst, the Physikalische u. Chemische Reichsanstalt, the Polytechnic in Charlottenburg, and the factory of the Berliner Königlichen Porzellan-Manufactur. I was not admitted to the factory itself, but was only shown the warehouses. In Göttingen itself, thanks to the kindness of the director of the Realschule, I inspected the laboratory and the physics classroom and once attended a chemistry lesson. Considering that I arrived in Göttingen only on July 13, new style, I could not tear myself away from laboratory work and decided to postpone acquaintance with the schools until my next trip.

Laboratory Assistant K. Trinakovsky.

Tomsk. March 1911.