Page:Popular Science Monthly Volume 49.djvu/144

132 , dotterel, and roseate tern; there are also eight plates and one hundred figures in black and white from original drawings, by G. E. Lodge, and three illustrations from photographs from Nature by R. B. Lodge. The execution of both illustrations and letterpress is excellent. It is perhaps too much to expect immaculate diction as well as scientific accuracy and a pleasing style in the same writer, but it does seem that a second thought would have prevented Mr. Hudson from saying, "The food of the cuckoo is exclusively insectivorous."



Dr. Ostwald has again laid the chemists of the world under obligations to him by a helpful discussion of the principles underlying a department of their science. Feeling that the scientific side of analytical chemistry had been left too far behind by the technique of the subject, he has undertaken to make available recent advances in chemical theory that are capable of throwing much light upon the processes of the analytical laboratory. The author points out that for the recognition of a substance only a few of its properties need be ascertained, for if the substance under examination agrees perfectly in some of its properties with a known substance, it will agree in all. It usually happens that we have a mixture of substances to examine, and the separation of these must precede their recognition. He next shows that separation is a mechanical operation and usually depends on transforming one substance after another into a different state of aggregation from the rest of a mixture. Chemical separation consists in such transformations, and is hence really a preparation for mechanical separation. In treating these processes the author discusses the theory of solution, an important law of which is that salts do not exist as such in aqueous solution, but are dissociated more or less completely into their constituents or ions. Other laws concerned in chemical separation are those of chemical equilibrium, the course of chemical reactions, precipitation, and those governing reactions attended with the liberation or absorption of gas and reactions accompanying the extraction of a dissolved substance from one solvent by means of another. To this chapter the author has added a section on electrolytic separation. Dr. Ostwald touches upon the measurement of the quantity of a substance that has been separated and recognized, or quantitative analysis, and then passes to the application of the laws just enunciated. This part of the work is arranged according to the usual analytic groups, and the behavior with reference to their ionic state of the substances treated is made especially prominent. The author holds that "if we adhere constantly to the point of view that analytical reactions are with very few exceptions reactions of ions, then a review of the facts of analytical chemistry becomes at once infinitely simpler."

One of the latest additions to the Library of Useful Stories is a popular sketch of geology. The author first calls attention to the earth's internal heat and to its effects in producing the rocks of mountains and volcanoes. He then shows how the materials of stratified rocks are produced and laid down and what a variety of fossil vegetable and animal forms are included in them. This brings him to the descriptions of the successive geological formations, from the Archæan to the gravels, which occupy the rest of the volume. The aim of the author has been "to tell the story of the Earth so that its past history helps to explain its present condition." To this end he constantly points out how familiar appearances result from the processes which he is describing, and he also draws especial attention to the information which fossils give us 