Chemistry and Physics. 479 



phenyl carbamine is unknown," although it might be feared that 

 the horrible odor of the isonitrile might discourage the beginner. 

 However, upon examining the book more carefully it is evident 

 that it presents a very interesting and useful course of laboratory 

 work. The author says that these experiments and tests have 

 been of personal value to hundreds of earnest students. This 

 can be well believed, as the course deals with many matters of 

 vital importance ; for instance, ,the examination of water, baking 

 powder, milk, ice-cream, cheese, headache-powders, paint and 

 oils, the detection of coal-tar dyes, food preservatives, arsenic, 

 methyl alcohol, the determination of food values, etc. As the 

 title of the book and its size indicate, the topics are treated in an 

 elementary manner, but it seems to be very well adapted for its 

 purpose. h. l. w. 



6. A Dictionary of Applied Chemistry • by Sir Edavard 

 Thorpe. Revised and enlarged edition, Vol. II, 8vo, pp. 786. 

 London, 1912 (Longmans, Green and Co.). — The second volume 

 of this important work extends from CHI to GOV. It contains 

 many important articles, and the matter appears to be well 

 brought up to the present state of the science. Among the 

 interesting longer articles are those on chlorine, coke manufacture 

 and the recovery of by-products, disinfectants, dyeing, identifica- 

 tion of dyestuffs on fabrics, explosives (73 pages), fermentation, 

 fertilizers, fuel, gas, glass, etc. The volume maintains the high 

 standard of the previous one as a valuable work of reference. 



H. L. W. 



7. Die tiussere lleibung der Case und ein neues Prinzip filr 

 Laftpumpen: Die Molekularluftpwnpe. — As early as 1875 Kundt 

 and Warburg showed that highly rarefied gases slip along the 

 walls of the containing vessel, and that the superficial friction of 

 the gas decreases with the pressure. In 1909 Knudsen calculated 

 the numerical value of the friction between the inner surface of a 

 glass tube and the stream of gas flowing through the tube, and found 

 good agreement between the experimental and theoretical data. 

 Quite recently W. Gaede has repeated Knudsen's observations 

 and found that, at pressures greater than - 001 mm of mercury, a 

 film or skin of gas is formed on the glass and that this layer is 

 predisposed to throw back the molecules in the general direction 

 of incidence. Furthermore, Gaede's experiments indicated that 

 the action of the gaseous skin may be fully accounted for in the 

 following- manner. Two kinds of unevennesses on the glass wall 

 are to be distinguished, (a) "mechanical" rugosities, and (b) 

 "molecular" inequalities. At pressures above 0-001 mm the mole- 

 cular unevennesses are covered up by a film of gas whose density 

 decreases towards the free interior of the gas. The gas molecules 

 which are reflected from the solid wall must pass through the skin 

 of gas and consequently their direction of emergence will be 

 affected. More specifically, normal passage through the skin is 

 the most favorable because, for oblique reflection, the length of 

 path in the skin is greater and hence oblique emergence is more 



