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POPULAR SCIENCE MONTHLY. 



gan, 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." 



GENERAL NOTICES. 



Dr. Ostwald has again laid the chemists 

 of the world under obligations to him by a 

 helpful discussion of the principles underly- 

 ing a department of their science.* Feeling 

 that the scientific side of analytical chemis- 

 try had been left too far behind by the 

 technique of the subject, he has undertaken 

 to make available recent advances in chem- 

 ical theory that are capable of throwing 

 much light upon the processes of the ana- 

 lytical 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 me- 

 chanical operation and usually depends on 

 transforming one substance after another 

 into a different state of aggregation from the 

 rest of a mixture. Chemical separation con- 

 sists in such transformations, and is hence 

 really a preparation for mechanical separa- 

 tion. In treating these processes the author 

 discusses the theory of solution, an impor- 

 tant law of which is that salts do not exist 

 as such in aqueous solution, but are dissoci- 

 ated more or less completely into their con- 

 stituents or ions. Other laws concerned in 

 chemical separation are those of chemical 

 equilibrium, the course of chemical reac- 

 tions, precipitation, and those governing re- 

 actions attended with the liberation or ab- 

 sorption of gas and reactions accompanying 

 the extraction of a dissolved substance from 



* The Scientlflc Foundations of Analytical 

 Chemistry. By Wilhelm Ostwald. Pp. 207, 12mo. 

 London and New York : Macmillan & Co. Price, 

 5a. net, $1.60. 



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 rec- 

 ognized, or quantitative analysis, and then 

 passes to the application of the laws just 

 enunciated. This part of the work is ar- 

 ranged 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 ma- 

 terials of stratified rocks are produced and 

 laid down and what a variety of fossil vege- 

 table and animal forms are included in them. 

 This brings him to the descriptions of the 

 successive geological formations, from the 

 Archaean 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 con- 

 stantly points out how familiar appearances 

 result from the processes which he is de- 

 scrii)ing, and he also draws especial attention 

 to the information which fossils give us con- 



* The Story of the Earth in Past Ages. By H. 

 G. Seeley, F. R. S. Pp. 186, 24mo. London : 

 George Newues, Ltd. Price, 1#. New York : D. 

 Appleton & Co. Price, 40 cents. 



