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LXII. Notices respecting New Boohs. 



Electrical Problems for Engineering Students. By William L. 

 Hoopee, Ph.D., and Boy T. Wells, M.S. Boston, U.S.A., and 

 London : Ginn & Company, 1902. Pp. vi + 170. 

 fl^HIS book of problems should prove very useful to teachers of 

 -*- electrical engineering. Starting with simple problems on the 

 calculation of resistance, the authors go on to the consideration of 

 the magnetic circuit, dynamos, alternating currents and alternators, 

 induction motors, and power transmission. Each chapter of pro- 

 blems is prefaced by suitable notes. In the cases which we have 

 tested, the answers are all correct. In some of the chapters, there 

 is a somewhat wearisome sameness about the examples. We can 

 confidently recommend the book as a yery suitable and useful one 

 for a class of engineering students. 



LXII I. Intelligence and Miscellaneous Articles. 



ON THE HEAT EVOLVED WHEN A LIQUID IS BROUGHT IN CON- 

 TACT WITH A FINELY-DIVJDED SOLID. BY TITO MARTINI. 



ANEW study upon the heat evolved when a liquid is brought into 

 contact with a finely-divided solid recently appeared in this 

 Magazine*. Mr. Parks displayed some new calorimetric results 

 obtained by the moistening of silica and sand, which he explains 

 by supposing that the heat evolved is due to the area of surface 

 that is brought into contact with the liquid, and that the heat 

 increases as the surface moistened is enlarged. 



In my own experiments regarding the Pouillet effect, which the 

 author has clearly recapitulated in his paper, before deciding to 

 advance an explanatory hypothesis, I thought of the possibility of 

 the calorific phenomena being due to the surface area in contact 

 with the liquid ; but 1 observed that an excessively fine powder of 

 quartz produced a result very different from precipitated silica. In 

 fact, while the first only produced very weak thermal effects, the 

 second manifested a considerable rise in temperature, whether in 

 contact with water or with other liquids (alcohol, ether, benzine, 

 &c). I then thought of measuring the quantity of liquid absorbed 

 by the two powders, with the result that precipitated silica absorbed 

 a much larger quantity of liquid than that absorbed by the 

 powdered quartz. 



In consequence of these results, it occurred to me to use another 

 substance that like silica was capable of being finely divided. 

 and make comparisons with this now precipitate and the same 

 substance reduced to powder. 



To this end, I used finely-powdered crystallized carbonate of 

 calcium and a precipitate of the same substance. Using the 

 method which I have already described in this Magazine f, I found 

 that the crystallized carbonate of calcium, moistened with acetic 

 ether, produced a rise of temperature of o, 26 C, absorbing 

 * Phil. Mag-. August 1902, p. 240. 

 f Phil. Mag. Maich 1899, p. 329, and Deceml ex 1900, p, 618. 



