ARTICLES 261 



And in the /3, or needle series : 



'd. propylene diamine -d. cobalt -f- d. propylene diamine 



-1. cobalt. 

 1. propylene diamine -d. cobalt + 1. propylene diamine 



-1. cobalt. 



Four compounds which are racemic to propylene diamine. 

 In the a, or prismatic series : 



Id. cobalt -d. propylene diamine -+- d. cobalt -1. propy- 

 lene diamine. 

 1. cobalt -d. propylene diamine + 1« cobalt -1. propylene 

 diamine. 



And in the ft, or needle series : 



'd. cobalt -d. propylene diamine + d. cobalt -1. propy- 

 lene diamine. 



1. cobalt -d. propylene diamine -f 1. cobalt -1. propylene 

 diamine. 



Finally, two completely racemic and inactive compounds of 

 the constitution 



d. Pn-d.Co + d.Pn-l.Co 4-l.Pn-d.Co -f l.Pn-l.Co 

 one in series a and one in series £, should be obtained by com- 

 bining in equimolecular proportions the pairs of oppositely 

 active partially racemic compounds included in brackets either 

 under 1 or 3 or under 2 or 4. 



All these predictions have been confirmed by actual experi- 

 ment, a result which, since optical activity is unquestion- 

 ably connected with molecular enantiomorphism, gives strong 

 support to those theories of constitution by which Werner 

 first brought into ordered arrangement one of the most com- 

 plicated and perplexing groups of compounds known to chemists. 



The new light which Werner's work has thrown on the 

 problems of molecular structure may be well-illustrated by a 

 brief consideration of the constitution of a well-known double 

 salt such as potassium chromium oxalate K 3 Cr(Ca04)3'3H a O. 

 Whilst satisfactory formulae for the simple constituent oxa- 

 lates are obtained by replacing the hydrogen in the formula 

 of the acid by an equivalent quantity of the metal a difficulty 

 arises in assigning a constitution to the double salt. How 

 are the simple salts and the water of crystallisation severally 

 combined ? 



