OF AKTS AND SCIENCES. 51 



I expressly admit that the mode of formulation is in each case per- 

 fectly arbitrary. 



The more carefully I have studied the subject, 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- 

 mines and cobaltamines upon Blomstrand's theory. While, thei-efore, 1 

 adopt this theory, I do so. because I think that with all its defects it 

 is by far the simplest and most comprehensive yet proposed. But 1 

 regard the particular structural formulas which I 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 cobaltamines, which are chiefly 

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

 that some of the cobaltamines 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 hexatoraic 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 determining 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 cobaltamines themselves still form 

 an extensive and most attractive field of labor. With all that has been 

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

 patient and conscientious labor. 



Cambridge, June 8, 1875. 



