OF ARTS AND SCIENCES. 69 



0.0432 gr. NH, and H 2 

 = 7.31% 

 1.7158 gr. gave 0.1027 gr. P,CUIg 2 = 3.83% P 2 0. 

 0.9806 gr. " 0.0567 gr. P 2 7 Mg, = 3.70% P 2 5 

 1.8903 gr. " 0.1321 gr. NH 4 C1 " = 3.20% (NH 4 ) a O 



In these analyses, the first determination of the phosphoric oxide 

 was made by double precipitation only, without subsequent treatment 

 with amnionic sulphide ; but in the second, this reagent was employed 

 in the manner above described. The ratio of AloO, to P 2 5 is almost 

 precisely 24 : 1, and the analyses correspond closely with the formula 



Acid salts of similar type occur frequently in the class of phospho- 

 molybdates, as in that of phospho-tungstates. 



24:1 Croceo-cobalt Salt. — The disposition of the cobaltamines to 

 form highly crystalline compounds, together with their well-defined and 

 various degrees of basicity, led me to study the relations of these bases 

 to the phospho-molybdic acids. This had already been done to a cer- 

 tain extent with the 5 : 1 atom series by Jbrgensen, whose results I 

 shall cite in connection witli that series. Neither roseo-cobalt nor 

 luteo-cobalt forms well-defined salts with 24 : 1 phospho-molybdic acid. 

 I had therefore recourse to croceo-cobalt,* the oxide of which may be 

 written 



Co,(NH 3 ) S (N0 2 ) 4 0, or, briefly, CcO. 



The chloride of this series gives no precipitate with solutions of 7 : 3 

 amnionic molybdate, or of hydro-disodic phosphate ; but in an acid solu- 

 tion of these two salts a solution of the chloride throws down a beau- 

 tiful bright yellow highly crystalline salt, which may be washed with 

 cold water. The portion analyzed was dried on woollen paper only. 

 Of this salt, — 



* Proceedings of American Academy, Vol. X. p. 1. 



