October 28, 191 5] 



NATURE 



227 



leals with conduction and convection of heat, and 

 Iiis is possible because at such a stage only a 

 iscriptive treatment of these subjects can be 

 a tempted. Other sections of the book deal with 

 e barometer and thermometer, expansion, eva- 

 loration and condensation, hygrometry, fusion 

 d solidification, specific heat, radiation, heat 

 nd work. Certain paragraphs are to be omitted 

 n first reading. 



Speaking generally, the authors have succeeded 

 n producing an interesting text-book, but in many 

 laces the statements are loose and not charac- 

 rised by that precision of language which it is 

 essential to inculcate in the mind of a beginner, 

 s on p. 19 the authors speak of the pressure 

 to 60 c.c. of water, and on p. 88 define the 

 fitish unit of heat as "the quantity of heat re- 

 ired to raise i lb. of water 1° F." This omis- 

 ion of " the temperature of " is a common occur- 

 rence in the text. Again on p. 20 we have an 

 experiment "To determine how much i c.c. of air 

 expands when heated." In this the temperature of 

 160 c.c. of air is raised from 15° C. to 85° C, the 

 amount of expansion being 40 c.c. The calcu- 

 lated expansion of i c.c. is 40/(160 x 70) = 1/280. 

 The authors then state : " an accurate and at the 

 same time convenient result is 1/273." On p. 140 

 paraffin-wax is not a suitable material to illustrate 

 melting point by the curve of cooling. In the 

 iagram on p. 40 the pressure gauge should be 

 nnected to the inner cylinder of the hypsometer. 

 he book contains a large number of questions 

 nd numerical exercises. 

 (4) Dr. Searle's "Experimental Harmonic 

 otion " is written on lines very similar to his 

 •ell-known manual on "Experimental Elasticity." 

 e subject-matter dealt with, however, is not so 

 ide as the title would seem to imply. The first 

 art of the book is devoted to the elementary 

 eory of harmonic motion, and is apparently 

 carried only so far as is necessary to understand 

 the experiments described in the second chapter. 

 There is no discussion of damped vibrations, com- 

 f)osition of harmonic motions, or the analysis of 

 periodic curves. The experiments described in the 

 second chapter (fourteen in number) are such as 

 are performed in the author's classes at the 

 Cavendish Laboratory. They include oscillation 

 methods for comparing moments of inertia, deter- 

 minations of the acceleration due to gravity, the 

 experimental study of a pendulum with yielding 

 support, and an investigation of a system with two 

 degrees of freedoni. A theoretical discussion of 

 lach experiment is given, and there are full prac- 

 tical details for the design of the apparatus to 

 insure satisfactory results. Each experiment is 



furnished with a typical series of data obtained in 

 NO. 2400, VOL. 96] 



an actual experiment. The exposition is clear, and 

 the book may be profitably read by university 

 students. Many teachers will welcome a book of 

 this kind on account of the precise details for the 

 setting up of the various experiments. 



I 



LABORATORY WORK ON COAL AND 



COAL-PRODUCTS. 



Laboratory Work for Coal-mining Students, By 



J. Sim and A. M. Wylie. Pp. viii+136. 



(London : E. Arnold, 191 5.) Price 2s. 6d. net. 



THE difiiculties associated with coal analysis 

 are determined in part by the fact that a 

 material which is consumed in tons has for con- 

 venience of manipulation to be tested in grams, 

 and in part by the variety of uses to which coal 

 is applied. The first necessitates merely extreme 

 care and method in sampling, but the second 

 requires a diversity of tests demanding the 

 greatest skill and experience. The most satis- 

 factory way of conducting a test is obviously to 

 submit a large sample of the material to the 

 special process to which it is subsequently to be 

 applied. This is frequently done; but it is not 

 described in the present volume, which is cori- 

 cerned with laboratory methods only. 



The difificulties attending coal analysis may be 

 realised when one considers the variety in com- 

 position as well as the chemical sensitiveness of 

 the substance. Coal Is no sooner exposed to the 

 air than it begins, especially when in powder, to 

 absorb oxygen and to evolve carbon monoxide 

 and dioxide. The sulphur which is present, 

 partly as organic sulphur and partly as pyrites, 

 also undergoes oxidation. Then, again, the 

 nature of the products and by-products, upon 

 which its value in the gas and coking Industry 

 depends, is determined by the character of the 

 coal as well as by the temperature at which these 

 products are extracted or distilled. For example, 

 It has been shown recently that extraction with 

 pyridine removes considerable quantities of para- 

 ffins, that distillation in vacuo gives rise to a series 

 of naphthenes (cycloparaffins), whilst ordinary 

 destructive distillation at high temperatures pro- 

 duces the coal-tar hydrocarbons. It would appear 

 from this that the original hydrocarbon of the coal 

 passes through various stages In the process of 

 heating. Finally, a knowledge of the thermal 

 value of the coal when used as fuel Is essential. 

 It will be seen that the investigation of a sample 

 of coal is not a simple affair. 



The present volume has been written with the 

 object of facilitating the laboratory work of a coal- 

 mining student, that Is, one who is studying the 

 scientific basis of the industry from every point 



