128 



NA TURE 



[June 6, 1901 



determine the relative positions of the atoms to one 

 another in the molecule. 



Space win not permit of any detailed discussion of 

 this theory ; a single example must suffice to illustrate 

 the manner in which it was applied by Wislicenus. 



By heating malic acid to 150° on an oil bath, it is con- 

 verted almost entirely to fumaric acid ; this he explained 

 by the diagrams 



If the malic acid be heated irom 170 — 200", 

 small quantitities of maleic anhydride are formed, 

 though even at this temperature the greater part is 

 converted as before to fumaric acid ; this, accord- 

 ing to the theory, is due to the existence in the 

 malic acid at the higher temperature of a certain 

 number of molecules in which the atoms have 

 swung round and assumed the positions indicated 

 below ; from which the formation of maleic 

 anhydride might be predicted : 



COOM 



\ 



tolane dichlorides and dibromides, mesaconic and citr- 

 aconic acids, the crotonic acids, &c ; among all the cases 

 he considered, there weie only two facts not in consonance 

 with those demanded by the theory ; these were (l) the 

 partial conversion of maleic into fumaric acid by the 

 action of bromine, and (2) the production of dibrom- 

 fumaric acid by the addition of bromine to acetylene- 

 dicarboxylic acid. 



In the following year (1888) he published a series of 

 papers {Licbig's Ann. Chcni. 188S, ccxlvi, 53 ; ccxlviii, I ; 

 1889, ccl, 224; cclxxii, i) containing the results of a 

 large number of experiments (carried out by himself 

 and his pupils) with the object of investigating the 

 nature, constitution and relationships between maleic 

 and fumaric acids, acetylene-dicarboxylic acids, the 



In the same way Wislicenus applied his theory to all 

 the other reactions of maleic and fumaric acids, to the 



NO. 1649, VOL. 64] 



<i-chlorpropylenes, the crotonic acids, the tolane di- 

 chlorides, &c. ; all of these tended to support the 

 hypothesis he had put forward. In the case of the two 

 apparent exceptions alluded to above, he showed that in 

 the first case the action is far more complicated than at 

 first appears, the conversion of the maleic into fumaric 

 being wholly accounted for by the formation of hydro- 

 bromic acid in the course of the reaction, which would 

 suffice to bring about the change. .Similarly in the 

 second case, by preventing the formation of hydrobromic 

 acid, the reaction is that demanded by theory, viz., the 

 formation of dibroni maleic acid. Thus the exceptions 

 strengthened rather than weakened the argument. 



It is only fair to call attention to the fact that Michael, 

 who has devoted considerable time to the investigation 

 of the subject, has obtained results which in many cases 



