S. E. Sheppard. Photo Chemistry (Text-Books of Physical Chemistry, edited by Sir William Ramsay). London, New-York, Bombay and Calcutta—1914. (461 pages).

In recent times a fairly considerable number of textbooks on photochemistry have appeared in the German language; Sheppard’s book is the first book written in English.

In the first chapter Sheppard gives a brief history of the doctrine of light and of its chemical actions; in the second chapter the laws and methods of optical observations are set forth. Then the units of luminous intensity are presented, with the English units described in detail and methods of photometry and spectrophotometry indicated. The third chapter treats the laws of radiation, giving data on the black body and describing methods for determining temperatures by optical means. In the fourth chapter the question of

economic coefficient of various light sources are discussed, and sources of ultraviolet rays are indicated. The fifth chapter studies in detail the absorption of light, Beer’s law, and the doctrine of chromophoric groups; it then briefly develops the theory of absorption (without mathematics, indicating only the results), and in the sixth chapter the author proceeds to photochemistry proper. Here Sheppard analyzes the general case of photochemical equilibrium and kinetics, considers reversible, irreversible, and pseudo-reversible reactions, and allotropic changes. The seventh chapter examines separate special cases of photochemical reactions, and the last four chapters (VIII, IX, X, XI) discuss the relation of matter to light and the appearance of light during reactions, and set forth in detail organic synthesis under the influence of light. In the textbook the author attempts to make use not only of the English literature, but also of the German; unfortunately, however, the exposition sometimes contains annoying inaccuracies in the transmission of results, and too little attention is paid to the fundamental laws. In any case, Sheppard’s book is a valuable aid which, together with the books of Plotnikow and Weigert, can introduce the beginner to the complex and rapidly developing field of chemical transformations under the influence of light.

P. Lazarev.