SCIENCE 



FRroAY, July 22, 1921 



CONTENTS 



Types of Valence: Dr. Irving Langmuir 59 



Professor S. Bruchmann : Professor Douglas 

 Houghton Campbell 67 



Scientific Events: — 

 Field WorTc of the Smithsonian Institution; 

 The Medical School of the University of 

 Virginia; The Science Club of the University 

 of Texas; Ths Rochester Meeting of the 

 Optical Society of America; American En- 

 gineers in Europe 68 



Scientific Notes an-d News 71 



University and Educational News 72 



Discussion and Correspondence : — 



The Geographic Distribution of Hybrids: 

 Dr. M. L. Fernald. Albinism in the Black 

 Bear: Paul C. Standlet. Bechhold's 

 '^Capillary Phenomenon" in Agricultv/re : 

 Jekome Alexander 73 



Quotations : — 



The Boyal Institution 74 



Scientific BooTcs: — 



Evermann and ClarTc on La'ke MaxinTcuckee : 



T. L. Hankinson 75 



Special Aritcles: — 



An Explanation of Liesegang's Rings: Dr. 

 Hugh McGuigan 78 



The North Carolina Academy of Science: C. 

 S. BrimitEY 80 



MSS. intended for publication and boolca, etc., intended for 

 review should be sent to The Editor of Science, Gairison-on- 

 Hudson, N. Y. 



TYPES OF VALENCE 



From the theory proposed by G. N. Lewis in 

 1916 and subsequently extended by the writer, 

 it is clear! that the term valence has been 

 used in the past to cover what we may now 

 recognize as three distinct types of valence, 

 viz.: 



1. Positive valence : the number of electrons 

 an atom can give up. 



2. N'egative valence: the number of elec- 

 trons an atom can take up. 



3. Covalence: the number of pairs of elec- 

 trons an atom can share with its neighbors. 



It was shown that these fundamental con- 

 ceptions of valence as well as the actual nu- 

 merical values of each type of valence for most 

 of the elements could be derived from a few 

 postulates regarding the structure of atoms. 

 The following method of deriving these rela- 

 tionships, however, is not only much simpler 

 than that previously given by the writer, but 

 throws a new light on the relationships be- 

 tween the different types of valence. 



We will take for granted the Rutherford 

 type of atom, which consists of a positive nu- 

 cleus surrounded by a number of electrons 

 equal to the atomic number of the atom. We 

 will also assume that Coulomb's law applies 

 to the forces between the charged particles in 

 the atom, but at the same time will recognize 

 the existence of repulsive forces in atoms which 

 prevent the electrons from falling into the 

 nucleus. For the present purpose, however, it 

 is immaterial whether the repulsive force is a 

 dynamic force (centrifugal force) such as 

 that assumed by Bohr, or is a static force as 

 postulated by G. IST. Lewis, J. J. Thomson or 

 recently by the writer.^ 



We shall need to make only 3 postulates in 



1 Langmuir, Jour. Amer. Chem. Soc, 41, 926 

 (1919), and Jour. Ind. Eng. Chem., 12, 386 (1920). 



2 Science, 53, 290, Mar. 25, 1921. 



