446 



SCIENCE. 



[N. S. Vol. XIX. No. 481. 



the uew idea was in close accord with facts. 

 Notwithstanding the enormous amount of 

 work and speculation of the past fifty 

 years, the idea of valence remains as 

 mysterious as ever. Whether valence rep- 

 resents certain lines of force as a result 

 of some modified application of chemical 

 affinity, or whether it represents certain 

 electrical charges, remains for the future 

 to determine. The electrolytic dissociation 

 theory and the ionization theory would 

 seem to point to the latter as one of the 

 coming theories. Every one must admit 

 that the present valence theory has been 

 of inestimable value in the development of 

 the science, yet none can doubt the fact 

 that the foundation upon which the whole 

 theory rests is by no means a firm one. 



The Theory of Double Salts: James Locke, 

 Massachusetts Institute of Technology, 

 Boston, Mass. 



The present theory of double salts is 

 untenable. In the development of the 

 double-salt theory during the past thirty 

 or forty years, the tendency has been to 

 represent even the most complex of these 

 double compounds as if the valences of the 

 respective elements were absolutely fixed. 

 This condition of affairs has been brought 

 about largely by the organic chemists who 

 have carried the stri;ctural arrangement 

 to the extreme, and many compounds are 

 represented by definite fixed formulas with- 

 out the slightest shade of reason. The 

 salts of hydroferro and hydroferrieyanic 

 acids serve as excellent illustrations. The 

 double salts of platinum, as represented by 

 Remsen in his theoretical chemistry, also 

 shoAV the absurdity of the present theory. 

 In fact, the present double-salt conception 

 is without foundation and must sooner or 

 later fall. The Werner theory comes 

 nearer to a logical representation of the 

 double salts than any theory which has yet 

 been proposed. 



Werner's Theory of Valence and the Con- 

 stitution of Compounds: J. E. Teeple, 

 Cornell University, Ithaca, N. Y. 

 The most common objection to Werner's 

 theory is that it discards the present theory 

 of valence, although Werner himself be- 

 lieves that it is only a logical outgrowth 

 of the valence theory. The development 

 of the present theory since the time of 

 Prankland and Kekule may be summed up 

 as follows: (1) A rise in the valence as- 

 signed to each element; (2) the increasing 

 use of compact concentric formulas; (3) 

 the common acceptance of the idea of 

 varying valence; (4) the introduction of 

 space relations in formulas, and (5) the 

 growth of the idea of partial or residual 

 valence. The results of the development 

 along these five lines have been remarkable, 

 notwithstanding the fact that no satis- 

 factory explanations are offered for any 

 of the complex compounds and especially 

 the double salts. In fact, Werner's theory 

 is the first to give a satisfactory explana- 

 tion of the structural formulas as CoCL • 

 6H,0, CoCl3-3NH3, C0CI3 -4(^13), Fe- 

 (CN)^K3 and FeCCN)„K,. 



To understand Werner's theory three 

 concepts are necessary: (1) Primary 

 valence, (2) secondary valence and (3) 

 coordinate number. By primary valence 

 is understood the idea of valence in the 

 ordinary sense as the power of holding to- 

 gether ions or radicals which usually unite 

 with ions. Secondary valence, on the 

 other hand, only combines substances which 

 can not act as ions and are not equivalent 

 to them. The coordinate number of an 

 atom represents the maximum number of 

 groups or atoms with which it may come 

 into .direct contact. This number is def- 

 inite and unvarying for each element : four 

 for carbon, six for cobalt and most of the 

 metals. The number can easily be de- 

 termined by its ammonia compounds or 

 similar derivatives. 



