OP ARTS AND SCIENCES. ,01 



I expressly admit that the mode of formuhition is iii each case per- 

 fectly arbitrary. 



The more carefully I have studied the siihject, the more full has 

 become my conviction that in the present state of our knowledge we 

 cannot assign absolutely definite structural formulas to the platina- 

 minesand eobaltamines u[)on Blomstrand's theory. While, therefore,! 

 a(loi)t this theory, I do so because I think tliat with all its defects it 

 is by far the simplest and most comprehensive yet proposed. But I 

 regard the particular structural formulas whicii 1 have employed sim- 

 ply as convenient illustrations, — provisional formulas which the pro- 

 gress of science may at any time modify. 



In my forthcoming work on the metals of the platinum group, I 

 shall describe a few other salts of the eobaltamines, which are chieiiy 

 of interest in connection with those metals ; and I hope also to show 

 that some of the eobaltamines are valuable analytical reagents. In 

 closing my labors, I wish again to direct the attention of chemists to 

 the advantages offered by this class of salts in investigations. We 

 have in croceocobalt, xanthocobalt, and luteocobalt, respectively, dia- 

 tomic, tetratomic, and hexatomie bases, possessing the important prop- 

 erty of forming extremely well-defined and highly crystalline salts. I 

 suggest the employment of these bases as means of detern)ining the 

 atomicities of relatively chlorous molecules, as, for instance, of the poly- 

 meric modifications of phosphoric acid, and in other cases in which our 

 knowledge is still imperfect. The eobaltamines themselves still form 

 an extensive and most attractive field of labor. W^ith all that has been 

 done, there is no part of this field which will not yield au abundant 

 harvest of interesting and theoretically valuable results. 



My grateful acknowledgments are due to my assistant, Mr. W. E. 

 Cutter, who has aided me in the analytical part of my work with most 

 paiieut and conscientious labor. 



Cambbidge, June 8, 1875. 



