OCTOBEE 14, 1904.] 



SCIENCE. 



493 



have attempted work of this character know 

 that months or even years of work are fre- 

 quently spent to obtain the synthesis of a 

 single compound. In spite of the wealth 

 of methods at our command — a wealth so 

 great that it is often very difficult to select 

 between several which are equally unprom- 

 ising—it is evident that these methods of 

 synthesis need improvement at many 

 points. Not only do we need new and 

 better methods, but many old methods re- 

 quire further study to disclose why they 

 succeed in some cases and fail in others and 

 to secure a fuller knowledge of secondary 

 reactions which often occur. As recent re- 

 markable achievements in this field of 

 synthetic methods may be mentioned the 

 brilliant results obtained by Grignard with 

 magnesium compounds, Bouveault's ele- 

 gant new solution of the old problem of 

 transforming an acid into the correspond- 

 ing alcohol and Scheuble's reduction of the 

 amides of bibasic acids to the corresponding 

 glycols. 



Work along the lines suggested needs to 

 be done in order to fill out and complete 

 our knowledge in a systematic way, and 

 occasionally work along such lines is re- 

 warded by results of epoch-making signifi- 

 cance, as when Gomberg discovered tri- 

 phenylmethyl in his endeavor to prepare 

 hexaphenylethane. Such work is not 

 likely, however, to greatly advance our 

 insight into the real nature of carbon com- 

 pounds and we all feel that there are far 

 more fundamental problems which demand 

 attention. 



As outlined above, the theories of valence 

 and of structure now universally accepted 

 imply a certain amount of knowledge of 

 the arrangement of atoms in space. So 

 far as the original and fundamental concep- 

 tions are concerned, however, this knowl- 

 edge is quite vague. The much more 

 definite conception proposed by van't Hoff 

 and in a somewhat different manner by Le 



Bel is, of course, familiar to you all. 

 In discussing any hypothesis it is always 

 important to have clearly before us the 

 facts upon which it is based. As I have 

 already hinted, I believe that the theory 

 of valence and the theory of structure in 

 the sense of a sequence of atoms within the 

 molecule are supported by our knowledge 

 of such a vast accumulation of consistently 

 interrelated phenomena that we are justi- 

 fied in believing that we have positive 

 knowledge with regard to the stinicture of 

 the molecules of organic compounds. I 

 am as ready as any one to demand that 

 every theory, no matter how old or how 

 universally accepted, shall be continually 

 brought back to the test of agreement with 

 experimental facts, but I am not willing to 

 admit that we may not, in the end, acquire 

 positive knowledge by the process of in- 

 ductive reasoning. 



Assuming, then, the fact of a knowledge 

 of the sequence of atoms in organic com- 

 pounds, we have this basis for van't Hoff's 

 hypothesis: (1) When four unlike atoms 

 or groups are combined with a single car- 

 bon atom optical activity results in such a 

 manner that there may always be found 

 two compounds having identical sequence 

 of the atoms within the molecule, and ex- 

 actly equal rotary power, but of opposite 

 signs. (2) That when two adjacent car- 

 bon atoms are combined each with three 

 unlike groups, two compounds may result 

 which, Avhile optically inactive and having 

 the same sequence of atoms, still differ in 

 physical properties. An illustration of 

 this is found in raeemic and mesotartaric 

 acids. (3) Rings containing five and six 

 atoms are formed with especial ease, those 

 containing three, four and seven atoms less 

 readily, and rings containing more than 

 seven atoms are scarcely known. (4) De- 

 rivatives of cyclopropane, cyelobutane, 

 cyclopentane and cyclohexane having two 

 substituents combined with different car- 



