252 PROCEEDINGS OP THE AMERICAN ACADEMY. 



unless a rather large excess of platinic hydrate is employed. When 

 this is the case a greater or less quantity of a deep orange-red solution 

 is sometimes formed, which on standing deposits a dark tarry mass in 

 case the sodic tungstate is employed. In place of sodic hydrate I have 

 also used baric hydrate in prejjaring a soluble form of the platinum 

 compound, but in this case also the platinic hydrate, according to 

 varying conditions, varied very much in solubility. 



When platinic hydrate is boiled with a solution of 10:4 sodic tung- 

 state the latter being in large excess, yellow solutions are sometimes 

 formed which on evaporation and standing yield large crystalline 

 masses with a fine yellow color and strong lustre. These crystals con- 

 sist essentially of the 10 : 4 sodic salt, 10 WO3 . 4 NagO + 23 aq., but 

 they contain a greater or less proportion of a platinic compound 

 which — water of crystallization apart — has probably the formula 

 10 WO3. PtOa . 4 Na^O, and which appears to be isomorphous with 

 the tungstate. A compound of this kind gave on analysis figures which 

 corresponded very closely with the formula, 



10 WO3 . PtOa . 4 Na.O + 2 {10 WO, . 4 NagO} + 72 aq. 



We may have here a combination of two isomorphous salts, hav- 

 ing respectively the formulae, IOWO3. PtOg . 4 Na^O + 26 aq., and 

 10 WO3 . 4 NaoO + 23 aq. The analyses of two different preparations 

 of the salts correspond very closely. 



The difficulty of obtaining definite compounds by direct solution of 

 platinic hydrate led me to another method, which may be used with 

 much advantage. Pure crystallized sodic tungstate is to be dissolved 

 in water, a rather large excess of sodic hydrate added, and a neutral or 

 nearly neutral solution of platinic chloride added to the boiling solution 

 in small portions at a time. Platinic hydrate is formed and instantly 

 dissolved. The chloride is to be added until a distinct excess of 

 Pt(0H)4 is present. Acetic acid is then to be added in small excess. 

 Alcohol then often throws down a dark tarry mass which contains one 

 or more saturated platino-tungstates. When the projjortion of platinic 

 chloride necessary happens to be exact, a beautiful orange-colored 

 clear solution is formed which on cooling or evaporation deposits an 

 abundance of beautiful yellow needles or prisms easily purified by 

 recrystallization. By this process a definite salt may be prepared in a 

 very short time and in large quantity. Different salts are, however, 

 formed under different conditions, and further investigations must show 

 whether it is possible by using definite quantities of platinic chloride 

 and of sodic tungstate to obtain uniform results as regards the constitu- 



