Chemistry and Physics. 507 



of porous earthenware. A large amount of mercury vapor dif- 

 fused through it when mercurous chloride was volatilized in it 

 and was condensed on the surrounding glass vessel. Further 

 when calomel is volatilized in a retort connected with a Sprengel 

 pump, by which the pressure is reduced to about 30mm. the upper 

 portion of the apparatus is covered with a layer of globules of 

 mercury, a corresponding quantity of mercuric chloride being 

 formed. Again pieces of caustic potash heated to the same tem- 

 perature became covered with orange mercuric oxide when 

 placed in the calomel vapor, and not black mercurous oxide. 

 Hence the authors conclude that mercurous chloride is Hg 2 Cl 2 , the 

 mercury in it not being univalent. — Ber. Berl. Chem. G-es., xxvii, 

 1482, June, 1894. G. f. b. 



6. A Text-book of Inorganic Chemistry. By G. S. Newth, 

 F.I.C., F.C.S. 12mo, pp. xiv, 667. London and New York, 1894. 

 (Longmans, Green & Co.) — The author has sought in this book 

 to obviate many of the difficulties arising from the attempt to 

 base a systematic course of elementary chemical instruction upon 

 the periodic classification of the elements, by dividing it into 

 three parts, the first of which is devoted to a brief sketch of the 

 fundamental principles and theories of the science, the second to 

 a study of the four typical elements hydrogen, oxygen, nitrogen 

 and carbon, and the third to a systematic treatment of the ele- 

 ments according to the periodic law. The first part is especially 

 worthy of notice since the more recent developments of the sci- 

 ence in a physico-chemical direction are included in it, and are 

 clearly though of course briefly, stated. Such subjects as the 

 kinetic theory of gases, dissociation, electrolysis, critical tempera- 

 ture and pressure, osmotic pressure and thermo-chemistry, for 

 example, are here included. The book is carefully written and 

 appears fully up to date. The centigrade scale of temperatures 

 is used exclusively and the metric system preferably ; though we 

 notice that the word " weight" for the most part is employed in 

 the sense of ' s mass." G. f. b. 



7. An Elementary Chemistry. By Geobge Rantout White, 

 A.M. 12mo, pp. xxx, 272. Boston, 1894 (Ginn & Company). — 

 This book is a laboratory manual and is intended for beginners in 

 chemistry. The first and second parts are devoted to experiments, 

 the latter being the more advanced. The third part comprises 

 the history and development of the laws and theories of chemistry. 



G. F. B. 



8. The mean density of the earth. — Prof. Potnting's essay 

 on the mean density of the earth has now been published. It 

 contains a review of previous methods together with an account 

 of the method of weighing by the ordinary balance which Prof. 

 Poynting adopted. Newton in his Principia estimated that two 

 spheres of the density of the earth, each a foot in diameter, would 

 if separated by a quarter of an inch and left to their own attrac- 

 tions, take nearly a month to come into contact. Prof. Poynting 

 points out that there is a mistake in the arithmetic, and that the 



