Chemistry and Physics. 61 



that a fifth edition has been called for so soon after the fourth 

 was issued. In the first edition, as the author tells us, the chief 

 aim was to show not only that hypotheses- and the theories based 

 upon them are necessary aids to chemical investigation, but at the 

 same time to assign to them their true value and to place them 

 in a position similar to that which they occupy in theoretical 

 physics. But this aim was an ephemeral one since it was local 

 in time. The fourth edition was therefore completely revised and 

 rewritten so as to give an account of the latest development of 

 chemical theories and at the same time, by giving the more im- 

 portant empirical data, to make the theoretical conclusions arrived 

 at easier to follow and to render clearer the causes leading to 

 their foundation. This edition was divided into three books ; 

 the first dealing with atoms and their properties, the second with 

 the Statics of the atoms or the doctrine of the equilibrium of the 

 atoms in their combinations with one another, and the third with 

 the Dynamics of the atoms or the doctrine of chemical change. 

 With reference to the title the author says : " I do not in the 

 least agree with the use of the term 'modern? when referring to 

 'chemistry* but only as I have used it in reference to the 'theories' ; 

 for in my opinion no change has been effected in chemistry in the 

 last hundred years, with perhaps the single exception of the pas- 

 sage from the phlogistic to the antiphlogistic system, which has 

 been of so revolutionary a character as to justify a line of de- 

 marcation between an old and a new or modern chemistry." The 

 fifth edition differs from the fourth chiefly in the use of atomic 

 weights recalculated by the author and Dr. Seubert, in certain 

 abridgments in the second book, and in certain changes in the third 

 book, particularly relating to the thermal phenomena accompany- 

 ing chemical action and to the action of mass. The sections now 

 found in Part First treat of " The Atomic Hypothesis," " The Spe- 

 cific Gravity of Gases as an aid to determine Atomic Weights," 

 "Determination of Atomic Weights by the aid of the Specific 

 Heat in the Solid State," " Determination of Atomic Weights by 

 aid of Isomorphism," and " Chemical Atoms." Those in Part 

 Second are: "Forms of Combinations of the Atoms; Types," 

 " Law of Atomic Linking," " Molecular Weight and Atomic 

 Linking of those Bodies 'to which xVvogadro's law cannot be 

 applied," and " The Chemical Value, Valency, or the Capacity 

 of Saturation of the Atoms." The sections in Part Third are : 

 " Chemical Change and its Causes," " Chemical Change pro- 

 duced by Mechanical Disturbance," " Heat as Cause and Ef- 

 fect of Chemical Change," "Influence of Mass on Chemical 

 Action," " Chemical Action of Light," " Chemical Change as 

 a Cause and Effect of Electricity ; Electrolysis," and " Stability 

 of Chemical Compounds." These subjects are treated with 

 the ability and thoroughness characteristic of the author, who has 

 himself contributed so largely by his own investigations to estab- 

 lish some of the most important conclusions reached. So that as 

 a whole the book seems to us one of the most important chemical 



