818 Mr. G. H. Livens on Rotational 



investigation, but so far no good theoretical explanation has 

 been obtained. 



From the enormous amount of experimental data collected 

 together by Landolt in his book * on this subject, it appears 

 that in most cases very simple empirical relations can be 

 constructed which represent the variability of the rotativity 

 of a dissolved substance. For solutions of active substances 

 in simple inactive solvents these relations usually assume 

 one of the three forms 



(i.) [>]=A + Bc, 



(ii.) [o>]=A + Bc + Cg' 2 , 



(iii.) [a>] = A+ c --^, 



where [©] is the specific rotation calculated in a manner 

 hereinafter described, and c the concentration of the solution; 

 A, B, C are constants depending on the nature of the 

 substances involved. 



In a few cases mentioned by Landolt and also in several 

 cases recently investigated by Patterson f , it appears that 

 the behaviour cannot be correctly represented by an em- 

 pirical relation of either of the above forms, and no other 

 form has as yet been suggested. The variability of [©] 

 with c for these cases is usually exhibited on a graph. 

 From a careful study of the curves thus obtained, however, 

 one realizes that there is a great deal of similarity between 

 them and that certain typical forms can be picked out. 

 The four curves given in fig. 1, which represent the relation 

 for ethyl tartrate dissolved in (i.) ethylidene chloride, 

 (ii.) a-bromonaphthalene, (iii.) benzaldoxime, (iv.) methyl 

 iodide, are taken from papers by Patterson and are typical 

 ones which show the general behaviour in the more 

 complicated cases. 



This short description may be claimed to represent the 

 general conclusions which have been drawn from the experi- 

 mental data in as far as it represents by far the largest 

 majority of known cases. There are of course a few 

 exceptional cases not included, and as they are not in accord 

 with the subsequent theoretical discussion they will be 

 reserved for future consideration. 



* Das optische Drehungsvermogen (Brunswick, 1898). 

 t Journal of Chemical Society (Transactions), 1908. 



