OF ARTS AND SCIENCES. 109 



VI. 



RESEARCHES ON THE COMPLEX INORGANIC ACIDS. 

 By Wolcott Gibbs, M. D., 



Rumford Professor in Harvard University. 



(Continued from Vol. XV. p. 21, June, 1879.) 



Presented June 25th, 1880. 



PHOSPHO-TUNGSTATES. 



The phospho-tungstates, as already stated, were discovered by Scheibler, 

 who gave provisional formulas for several different compounds. As 

 the German chemist has published nothing farther upon the subject 

 for six years, and as the study of these compounds seemed to be a 

 necessary preliminary to that of other complex inorganic acids, I have 

 devoted much time and labor to them. The investigation has proved 

 very difficult and tedious, but has yielded results which, if not in all 

 cases perfectly definite and conclusive, are yet as I think valuable 

 and interesting. The difficulties met with in the study of this class 

 of salts are in some respects analogous to those which present them- 

 selves in the case of the alkaline tungstates. They are mainly as 

 follows : — 



1. The normal alkaline phospho-tungstates are readily decomposed 

 by water, yielding acid salts which are often very complex. These 

 acid salts are very slightly soluble, and cannot in general be recrystal- 

 lized for analysis. They are formed in greater or less proportion 

 whenever we attempt to purify the neutral or less acid salts by re- 

 crystallization. In many cases the ratio of tungstic and phosphoric 

 oxides in the neutral salt is changed when the acid salt is formed, so 

 that we can draw no certain conclusion from the constitution of one 

 salt as to that of the other. It is usually very difficult, or even impos- 

 sible, to pass from the acid back to the primitive normal or neutral 

 salt, because the addition of an alkali produces new compounds. 



2. It is difficult by any analytical method which has been devised 

 to determine the percentage of phosphoric oxide with great accuracy, 



