THE CHEMICAL PROBLEMS OF TO-DAY. 367 



while rings of six or five atoms easily form, it is more difficult to com- 

 bine fewer atoms, four or three, to a closed chain. The cause of this 

 fact Baeyer recognized as lying in the stereometric conditions. The 

 angles which the sides of a regular hexagon and pentagon form with 

 each other very nearly coincide with those in which the directions of 

 the valencies of the carbon atom intersect each other, and thus in 

 linking five or six atoms together the circle, so to speak, closes itself, 

 while if more or less atoms are present this can only be arrived at by 

 strong deviation of the directions of affinity. 



But still more surprising discoveries were hidden in van't Hoff's the- 

 ory. The gifted Dutch thinker had penetrated to the idea that two 

 atoms which are linked together by a single valency rotate freely around 

 an axis the direction of which coincides with that of the linking valency, 

 but that this rotation is stopped as soon as double linking takes place. 

 This latter is an immediate c )nsequence of the tetrahedric conception. 

 If I stretch out my two fore-fingers and let their points touch each other, 

 then the hands can rotate around them as an axis ; but if I stretch both 

 thumbs and both fore-fingers and allow their corresponding points to 

 touch each other, then a system results in which rotation is impossible. 



These two propositions of van't Hoflf, having remained almost un- 

 noticed for a decade, have lately come into great prominence. In a series 

 of important researches Johannes Wisliceuus has proved that apply- 

 ing these propositions and at the same time considering the specific 

 affinities of the groups or elements present, the stereometric aggrega- 

 tion of the atoms in certain molecules can be determined with prob- 

 ability. In an ingenious manner he has utilized the addition phenomena 

 shown by carbon atoms trebly linked together for an interpretation of 

 a stereometric aggregation of the atoms in the compounds formed. 



Wisliceuus, applying van't Hoff's ideas with courage and strictness, 

 has advanced organic chemistry in an important manner and has opened 

 a field for experimental research, which heretofore had been avoided 

 with a precaution suggestive of timidity. 



New discoveries came from other sides. An intimate research into 

 the oxims of benzil lead to the surprising result that the validity of the 

 second proposition of van't Hoff is not without exception. Cases were 

 noticed in which the free rotation of carbon atoms united by a simple 

 bond, which van't Hoff' disclosed, did not obtain. Further inquiry into 

 this subject led to a renewal of the question, " What does chemical 

 valency really meau?"' A question to which the mind incessantly de- 

 mauds an answer. It had long since been suggested that valency had 

 some relation to the electric behavior of the atoms. The chemistry of 

 the day expresses Faraday's fundamental electrolytic law thus : An 

 electric current which flows through several fused electrolytes severs 

 in each of them the same number of valencies^ not of atoms. 



It was found by von Helmholtz that those quantities of electricity 

 which, during the electrolytic process, move with the ions are dis- 



