64 



SCIENCE 



[N. S. Vol. XXVII. No. 680 



methods, and the day is far distant, if it 

 ever comes, when cellular physiology shall 

 be nothing but applied physics and chem- 

 istry. We can not foresee a time when 

 purely observational and descriptive bio- 

 logical studies, which to-day hold the first 

 place, shall not continue to have their 

 value. They represent the direction which 

 makes the strongest appeal to the great 

 majority of naturalists. The broadest gen- 

 eralizations hitherto attained in biology, 

 the doctrine of the cell as the vital unit and 

 the theory of organic evolution, have come 

 from this biological, as distinguished from 

 physical, direction of investigating living 

 organisms, and were reached by men with 

 the type of mind of the pure naturalist, 

 who loves the study of forms, colors, habits, 

 adaptations, inheritances of living beings. 



It is well that the sciences of nature hold 

 out attractions to so many different types 

 of mind, for the edifice of science is built 

 of material which must be drawn from 

 many sources. A quarry opened in the 

 interest of one enriches all of these sci- 

 ences. The deeper we can lay the founda- 

 tions and penetrate into the nature of 

 things, the closer are the workers drawn 

 together, the clearer becomes their com- 

 munity of purpose, and the more signifi- 

 cant to the welfare of mankind the up- 

 building of natural knowledge. 



William H. Welch 



The Johns Hopkins Univeesitt 



'.SCIENTIFIC BOOKS 

 Neure An^cliauungen auf dem Oehiete der 

 Anorganischen Chemie. By Adolph Wer- 

 ner. Braunschweig, Vieweg und Sohn. 

 1905. Pp. xii -f 189. Price 6 marks. 

 The book before us presents a system for 

 classifying inorganic compounds in such a way 

 that " complex salts," " molecular compounds," 

 hydrates, etc., as well as simple substances, 

 may be included. The fundamental idea 

 which underlies Werner's scheme is a new con- 

 ception of valence. It is a well-established 



fact that in many eases compounds in which 

 all of the valences of the individual atoms 

 seem to be fully saturated, still possess the 

 power of combining with other similarly satu- 

 rated compounds to form complex salts. From 

 this fact Werner draws the conclusion that we 

 must drop our idea of independent, definitely 

 directed valences. In place of this conception 

 he introduces that of " affinity " — an attractive 

 force acting, in the manner of an electrical 

 charge on a sphere, from the center of the 

 atom and uniformly distributed on its surface. 

 Valence is then simply an empirical relation 

 regarding the efFect of this force on other 

 atoms. Through considerations based on 

 manifold experimental data he decides that 

 this valence — the manifestation of " affinity " 

 — must be of two kinds which he calls, re- 

 spectively, principal and subordinate valence. 

 The former produces the combinations of 

 atoms met with in ordinary salts, giving rise 

 to ionizable radicles; this property can be ex- 

 pressed in modern terms by saying that prin- 

 cipal valences can bind atoms or molecules to 

 electrons. Subordinate valences are also ac- 

 tive in joining atoms to atoms, but in no case 

 can they produce ionizable substances. Thus 

 in the case of compounds between platinum, 

 ammonia and chlorine we have the follow- 

 ing series of compounds in which CI outside 

 of the brackets represents ionizable chlorine — ■ 

 primary valence — and that enclosed by the 

 biackets non-ionizable chlorine — subordinate 

 valence : 



[PKNIT^yci,; [pt(N^')=]ci,; [pt^^J/^^^^Jci, ; 



It will be seen that the total number of mole- 

 cules bound directly to platinum is a constant 

 — six — called by Werner the " coordination " 

 number. He has found that for all of the ele- 

 ments forming " complex salts " this " coordi- 

 nation number " is either four or six. 



That there is ground for Werner's dissatis- 

 faction with the present conception of valence, 

 no one can doubt, especially after reading the 

 introductory chapters of this book. It is 

 equally clear that in his new classification 



