GIBBS. — COMPLEX INORGANIC ACIDS. 253 



tion of the salt formed. It is indispensable to employ pure platinic 

 chloride or chlorplatinates. Even traces of iridium give a greenish 

 tint to the platino-tungstates formed, a fact which misled me in my 

 earlier experiments. Contrary to my preliminary statement, I now 

 find, on more prolonged study, no isomeric platino-tungstates. 



10:1:6 Sodic Platino-tung state. 12:5 sodic tungstate very readily 

 dissolves platinic hydrate in its soluble form, and gives a fine deep 

 orange-colored solution which on standing yields a mass of ill defined 

 dull orange crystals. These may be redissolved, recrystallized, and 

 dried on woollen paper. Of these crystals : 



1.1460 grams gave 0.8430 gram Pt + WO3 — 73.56 per cent. 

 1.1806 grams gave 0.0686 gram Pt + WO3 = 73.57 " 

 1.1806 grams gave 0.0706 gram platinum = 5.98 " 

 1.1460 grams gave 0.8695 gram platinum ^= 6.06 " 

 1.8770 grams gave 0.7774 gram WO3 = 67.83 



0.8770 gram lost on ignition 0.1397 gram oxygen and water, 

 = 15.93 per cent. 



The analyses lead to the formula, 



10 WO3 . PtOa. 6 NaaO + 28 aq., 

 which requires : — 



Calculated. Mean. Found. 



10 WO3 2320 67.79^ 67.65) 67.56 67.83 



\ 74.40 } 74.65 



PtOa 226.5 6.61 ) 7.00 j 6.96 



6 Na.O 372 10.87 ) 10.51 



V- 25.60 

 28 H2O 504 14.73 ) 14.94 



3422.5 100.00 



The soda being estimated by difference. It is remarkable that this 

 salt contains six molecules of base instead of four, all known silico- 

 tungstates being tetrabasic. The solution of this salt when shaken 

 with a solution of potaSsic bromide gives an amorphous pasty mass 

 with a deep orange-red color. In the analysis of this class of com- 

 pounds it is best to determine the platinum by ignition with sodic 

 carbonate. On treatment of the fused mass with water, the plati- 

 num remains as metal, and the tungsten may then be determined 

 in the filtrate in the usual manner. Nearly all the analyses were 

 made in this way, sodic oxide being determined by difference. In 

 some cases, however, tungstic and platinic oxides were precipitated 

 together by mercurous nitrate and mercuric oxide. 



