NATURE 



[September 2, 19 15 



above 100° C, since otherwise the engine will fre- 

 quently misfire " ; considering that Pratt's spirit 

 usually gives a little under 60 per cent., distilling 

 below 100° C, and many petrol substitutes con- 

 siderably less, this seems a misleading statement. 



On p. 45 we are told that "the vapour pressure 

 must be considered in storing naphtha and other 

 inflammable liquids," but it is now being recog- 

 nised that the determination of this factor is also 

 of the greatest importance in forming a sound 

 conclusion as to the ease of starting and flexibility 

 in running with a motor spirit, as the amount of 

 vapour given off at atmospheric temperatures 

 governs the formation of the explosive mixture in 

 the cylinder when starting from cold. 



Directions are given for determining the vapour 

 tension by introducing the petrol into the Torri- 

 cellian vacuum above the barometric column in a 

 10 mm. diameter tube, but a far more simple and 

 practical method is to use the pressure tube de- 

 vised by Sir Boverton Redwood and Captain 

 Thomson, which is adopted for testing the pres- 

 sures developed in vessels containing petrol. 



Several pages are devoted to the viscosity of 

 oils and testing their lubricating value, and also 

 to the setting point and fluidity of oils, their value 

 for gas-making and tendency to resinification. 



The book is, like most of the technical works 

 of German origin, a model of abstracting, and 

 invaluable as giving full references to original 

 work, but its utility is discounted in the laboratory 

 by the absence of practical detail. 



Chapter ii. is devoted to natural asphalt, and 

 contains much useful information on the subject ; 

 chapter iii. deals with ozokerite and Montan wax ; 

 whilst in chapter iv. we come to the important 

 subject of the tars obtained by the distillation of 

 coal, lignite, shale, and peat. 



The attention devoted to the recovery of the 

 coal-tar products in Germany led one to hope that 

 this part of the book would contain much valuable 

 information, but unfortunately the subject is not 

 treated very fully, and points of such importance 

 as the differences in tars due to variations in the 

 temperature of carbonisation receive but scanty 

 notice, whilst the use of the products of tar distil- 

 lation is dismissed with the curt remark that 

 " these are of great importance in the preparation 

 of dye-stuffs and of pharmaceutical products." It 

 might have been expected that special attention 

 would have been devoted at the present time to the 

 detection, estimation, and purification of those tar 

 products used in the production of high explo- 

 sives, but even the fact that it is the source of the 

 most important explosives of the day is not men- 

 tioned. 



The saponifiable fats and their technical pro- 

 NO. 2392, VOL. ,96] 



ducts are a very useful section of the book, which 

 ends with a chapter on waxes. Prof. E. Mueller 

 is to be congratulated on the translation of the 

 original German work, and the type, illustrations, 

 and general style are of the excellence always 

 found in Messrs. Wiley's technical publications. 



ELECTRICAL ENGINEERING. 



(i) Continuous-current Electrical Engineering. 



By W. T. Maccall. Pp. viii + 466. (London: 



University Tutorial Press, Ltd., 191 5.) Price 



I05. 6d. 

 {2) Single-phase Electric Railways. By E. Austin. 



Pp. xiv + 303. (London : Constable and Co. , 



Ltd., 1915.) Price 215. net. 

 (i) 1\ /[" R- MACCALL'S book is well above the 

 IVX standard usually found in books which 

 cover such a wide field, and it can be thoroughly 

 recommended, both to engineers and to students. 

 To the latter, the large selection of questions will 

 be of especial value. The book covers the 

 ground indicated by its title about as thoroughly 

 as could be expected in a volume of its size and 

 price; the most noteworthy omission is the sub- 

 ject of primary batteries. More might have been 

 said about electric heating, a little about electric 

 cooking, and electric furnaces might at least have 

 been mentioned. 



The chapters on illumination and lamps are 

 very good indeed, and contain little that we would 

 wish to alter. But those on machines, although 

 quite up to the standard of most text-books, are 

 certainly less satisfactory. Here and there the 

 matter is rather weak. Thus the portion dealing 

 with generator characteristics does not show that 

 real grip of the subject which an instructor ought 

 to have. Another point is the geometry of the 

 armature winding diagrams. A developed dia- 

 gram is shown with the poles behind, the commu- 

 tator helow, and the numbers running from left 

 to right ; while a radial diagram has clockwise 

 rotation of the numbers. These are not consistent 

 with one another. 



We do not think the author has ever tried to 

 separate the no-load losses of a machine in any 

 of the ways he has described, or we should have 

 seen some doubts expressed as to the validity of 

 some of them. In fact, he would probably have 

 found, as we ourselves once did, that the " friction " 

 alone, as determined from the constant speed ex- 

 periment, exceeds the " friction + hysteresis " 

 given by the constant flux experiment. In short, 

 this method won't work, for it assumes that the 

 frictional torque is the same at all speeds, which 

 is very far from the truth. The running down 

 test can be carried out much more simply than 

 in the manner described, and it can be modified 



