GIBBS. — COMPLEX INORGANIC ACIDS. 251 



XI. 



RESEARCHES ON THE COMPLEX INORGANIC ACIDS. 



By Wolcott Gibbs, M. D., 



Rumford Professor Emeritus in Harvard University. 



Presented August 1, 1894. 

 (Continued from Vol. XXI., page 128.) 



Platino-Tdngstates. 



In a notice of these and corresponding compounds of molybdenum 

 published some years since,* and intended to be only preliminary, I 

 pointed out the analogy between them and the silico-tungstates of 

 Marignac. The notice in question requires correction in several par- 

 ticulars, and I shall here give the results of a more complete investiga- 

 tion, conducted with better facilities for work and with a much wider 

 acquaintance with the whole class of complex acids. 



Platiuic hydrate, like silicic hydrate, dissolves when boiled with 

 solutions of alkaline tungstates belonging to the meta-tungstic series. 

 Platiuo-tungstates are formed under these circumstances, but various 

 conditions require to be considered. In general I have been accus- 

 tomed to prepare the hydrate Pt(OH)^ by Fremy's method, that is, by 

 boiling a solution of platinic chloride with a large excess of sodic 

 hydrate for some time and then adding acetic acid in small excess, 

 when the platinic hydrate separates as a pale buff-yellow slimy com- 

 pound to be washed by repeated decantation with cold water. When 

 the last portions of saline matter have been removed the wash-water 

 becomes turbid and settles only after very long standing. The hydrate 

 obtained in this way sometimes dissolves very readily in hot solutions 

 of alkaline tnngstates, sometimes only after long boiling, and sometimes 

 IS almost insoluble. The process is therefore an uncertain one at best. 

 The platino-tungstates formed have a yellow or orange-yellow color 

 and in many cases crystallize well. By the process which I have 

 given it is usually difficult to obtain perfectly saturated compounds 



* Berichte der deutschen chemischen Gesellscliaft, X. 1384. 1877. 



