Bibliography

D. Balarew, Der disperse Bau der festen Systeme. Allgemeine Theorie der Verunreinigung fester Systeme, pp. VI + 240, with 45 figures in the text, Dresden and Leipzig, Theodor Steinkopff, 1939.

D. Balarev, Disperse Structure of Solid Systems, Dresden—Leipzig, Theodor Steinkopff, 240 pp., 1939.

The book by the Bulgarian scholar Prof. Balarev, published last year, is a monograph devoted to the question of impurities in solid crystalline precipitates and to ways of avoiding these impurities. The book is of undoubted interest to analytical chemists and to persons working in inorganic preparative chemistry. However, the author approaches these questions not empirically, but from the standpoint of a “general theory of contamination of solid systems,” based on his ideas concerning the disperse structure of crystalline precipitates. Therefore the book is also of certain interest to physical chemists and to physicists concerned with the theory of crystals.

The author’s basic idea, which he has pursued in his investigations over a number of years, is that when crystalline masses are separated from solution, the real crystals formed are never ideal single crystals, usually considered in theories of crystal growth, but are complex conglomerates of intergrown elementary crystallites, possessing an almost colloidal degree of dispersity.

These ideas are close to modern theories of the mosaic (or block) structure of solids, which, in Bragg’s opinion, constitutes the most urgent problem in the theory of the structure of crystals. Unfortunately, the author devotes too little attention in his book to these theories of mosaic structure. The arguments he adduces in favor of the “almost colloidal” degree of dispersity of crystallites are purely qualitative in character and therefore not very convincing.

The boundaries of elementary microcrystallites create within a real crystal a large internal surface on which “internal adsorption” of the components of the mother solution and its impurities must take place. Therefore the contamination of the entire crystalline mass precipitating from solution is a function of the degree of dispersity of the elementary crystallites and of their arrangement, i.e., of the magnitude of the gaps, channels, and capillaries remaining between them.

The struggle against impurities, especially important in the preparation of substances intended for work in analytical chemistry and for determining the atomic weights of elements, consists in obtaining crystalline precipitates of such a structure in which “internal adsorption” would be reduced to a minimum.

From this point of view, the most advantageous are a large size of the elementary microcrystallites and minimal gaps between them. The author indicates general conditions favorable for obtaining such a structure of crystalline precipitates.

In the special part of his book (occupying the last 45 pages), the author applies the rules described above to three types of finely crystalline precipitates that are of the greatest practical importance in analytical chemistry and therefore have been studied in considerably greater detail than all others: barium sulfate, magnesium ammonium phosphate (and magnesium pyrophosphate), and the sulfides of heavy metals.

Especially with regard to the first of these substances, analytical practice has developed a number of techniques that ensure the best results. The author explains these rules from the standpoint of his theory. As for magnesium phosphates, the author uses the theory of “internal adsorption” to select the most precise method for determining the phosphate ion and confines himself to Schmidt’s method; for determining the magnesium ion he does not find a sufficiently reliable analytical method. The practical applications of the theory of “internal adsorption” are still less developed in the case of the precipitation of sulfides.

The book presents extensive experimental material, collected by the author himself and also painstakingly selected by him from the literature in order to substantiate the propositions he advances. The abundance of experimental facts described and the extreme detail of the exposition make Prof. Balarev’s book rather difficult to read; however, reading is facilitated by the fact that at the end of each of the twelve chapters of the book a brief summary of the chapter’s contents is given.

A. Rabinovich, Moscow