24 



NATURE 



[September 13, 19 17 



than with either physics or chemistry. Without a 

 sound knowledge of at least the fundamental 

 principles of these two sciences, the scientific 

 treatment of smoke abatement is bound to suffer, 

 and the result is that the scientific part, if it may 

 be so called, is ill expressed and arranged, 

 incomplete, and often incorrect. For example, 

 the term " British Thermal Unit " is defined and 

 used ; but the method of estimating the calorific 

 value of fuels is never mentioned, or its relation 

 to temperature, though the two are frequently 

 referred to together. The confusion between 

 molecular and atomic weights (p. 16) is not perr 

 haps a serious error, but the statement that at 

 low temperatures "hydrogen and carbon in the 

 coal partially combine, producing hydro-carbons 

 causing smoke " (p. 15), cannot be passed over 

 so lightly. The statement on p. 12 that excessive 

 admission of air produces carbon monoxide must 

 surely be an oversight. 



The author is evidently more at home with 

 furnaces, boilers, and mechanical stokers, and the 

 fact that he has qualified as smoke inspector by 

 examination of the Royal Sanitary Institute 

 explains the clear and full descriptive account of 

 these appliances, together with various forms of 

 g"as-producers and fire-grates. Everyone must 

 sympathise with the vigorous condemnation 

 levelled by the author against smoke and those 

 responsible for it, but we doubt whether the 

 volume before us, either by suggestion or experi- 

 ment or new appliances, has thrown very much 

 fresh light on the problem, or added many facts 

 to those already known. J. B. C. 



Laboratory Manual of Bituminous Materials fort 

 the Use of Students in Highway Engineering. 

 By Provost Hubbard. Pp. xi+153 (New 

 York : John Wiley and Sons, Inc. ; London : 

 Chapman and Hall, Ltd., ,1916.) Price 6s. 

 net. 



Since the advent of the motor-car the use of 

 bituminous materials in road-making has become 

 more and more widespread, and a definite know- 

 ledge of the chemical and physical characters of 

 these substances is of increasing importance to 

 the road constructor. In the United States a 

 number of the leading universities have instituted 

 courses of instruction in highway engineering, 

 which include laboratory practice in the testing of 

 bituminous materials, and the manual under notice 

 has been prepared by the author to meet the wants 

 of students and instructors attending such courses. 

 ^ The first part of the book deals tvith the defini- 

 tion and classification of the various bituminous 

 substances used by the highway engineer, and 

 also with general matters such as the sampling 

 and preparation of the bitumens for analysis. In 

 the second and main division the author describes 

 the methods of applying the various tests — 

 chemical, physical, and mechanical— by which the 

 materials are assayed and evaluated. The de- 

 scriotions are lucid and concise ; they have 

 evidently been drawn up by a writer who has 

 first-hand knowledge of the special difficulties 

 attending this class of analytical work. In the 

 NO. 24q8, vol. 100I 



concluding part of the book the characteristics of 

 the more important bituminous substances are 

 discussed, including those of the fluid, semi-solid^ 

 and solid petroleum products, tars, asphalts^ 

 pitches, creosote oils, and bituminous aggregates. 

 Typical analyses are given, and these are carefully 

 dissected in order to bring out clearly the proper 

 interpretation of the results. The book should 

 prove of value to municipal and other chemists 

 who may have to deal with the substances in 

 question, as well as to the students for whom it 

 is especially written. C. S. 



THE DANGERS OF ELECTRICAL 

 CURRENTS. 

 /^N account of the widespread use of electricity 

 ^-^ at the present time, the small book before 

 us, by M. Rodet,' is of considerable practical 

 value. We note that an actual current must pass 

 through the tissues of the body if any effect is to 

 be produced. A static charge is harmless. A 

 bird may perch on a high-tension main without 

 any serious results. The resistance of the human 

 body resides chiefly in the skin, and is very high 

 if the skin is dry — from 20,000 to 80,000 ohms. 

 But if the skin is moist and a good earth contact 

 is made by bare feet in a wet mass, a man may 

 be killed by touching a loo-volt main. A brief 

 summary is given of the general physiological 

 effects of stimulating various nerves by electrical 

 currents. The development of heat is also dis- 

 cussed : burns are produced where the current 

 density is great, as when it enters by a relatively 

 small contact surface. With respect to high- 

 frequency alternating currents, the ' interesting 

 experiments of Kennelly and Anderson in America 

 are described. They showed that, at an alterna- 

 tion of 100,000 per second, a voltage of 250 can 

 send a current of half an ampere through the 

 body without any sensation beyond that of 

 warmth. The explanation is probably that given 

 by Nernst, namely, that certain ions in the nerves 

 must attain a certain minimal local concentration 

 in order that stimulation may take place. Each 

 half-wave of so rapid an alternation cannot, in 

 the time permitted, effect this concentration before 

 the opposite half-wave comes in and reverses what 

 little has been done. The energy of the current 

 is thus converted into heat without being able to 

 produce electrolytic changes. 



'The second chapter is devoted to the nature 

 of the accidents which may happen. These are 

 indirect and direct. The former are due to a 

 momentary shock, harmless in itself, but which 

 may cause a fall from a height or similar result. 

 The protection is obvious : to take care either 

 that no live wires are within reach, or that the 

 workman wears eflficient insulating gloves, stands 

 on insulators, and so on, if disconnection from 

 the generator is Impossible. The direct accidents 

 are due to actual passage of current through the 

 body. So many different effects are possible that 

 it Is frequently a matter of difficulty to say what 



1 " Actiops Physiologiqiies et Dangers des Courants Electriques." Par 

 J. Rodet. (Paris : Gauthier-Villars et Cie, 1917.) Price 3.25 francs. 



