mNERALOGY; WITH A CLASSIFICATION OF SILICATES. 8S 



It was in 1861 that Marignac made known the existence of two types of silieotuugstates, in 

 which one molecide of SiO. is nnited respectively with ten and twelve molecules of "WO.. 

 Subsequent studies by Scheibler, made us acquainted with series of phosphotungstates 

 in which six molecules and twenty molecules of WO,j are united with one of P.O.-, ; while 

 Henri Ste-Claire Deville and Debray made known analogous phosphomolybdates. Wolcott 

 Gibbs has resumed the study of these various compounds, designated by him "Complex 

 Inorganic Acids," and has greatly extended our knowledge of them. He now recognizes a 

 series of metatungstates, the lowest of which, considered as an acid, is 4W0;j. H2O, and the 

 highest 16W0.i. TH.O ; while he finds not less than ten phosphotungstates, constituting a 

 homologous series ; " the homologizing term " being 2'WO.,,, the extremes 6W0,. P,0.-,. 

 6H2O, and 24W0;,. P2O.,. GH.O, and the salts apparently 12-basic. Similar series are got 

 for molybdenum, and arsenic, vanadic and antimonic oxyds may replace the phosphoric 

 oxyd in these compounds. Hypophosphorous and phosphorous and metaphosphoric acids 

 may also take the place of phosphoric acid in these complex salts, and portions of the 

 oxygen in molybdic and tungstic oxyds may be replaced by fluorine, while hydro- 

 carbon radicals like ethyl, methyl, and phenyl, appear also to be capable of entering into 

 the compounds. 



§ llY. The silieotuugstates of Marignac haA'e also been the subject of farther general- 

 ization by Gribbs, and it is found that the molecule of silica therein may be replaced by the 

 oxyds of platinum, selenium and tellurium, etc. The oxyds of tin, titanium, zirconium, 

 niobium and tantalum also appear to form similar combinations with the tungstates and 

 molj^bdates. All of these series of salts are soluble in water and crystallizable, generally 

 assuming cliuoi'hombic or anisometric forms. Nor are these complex salts confined to the 

 compounds of tungsten and molybdenum ; Gribbs has found several new series made up 

 from vanadic with phosphoric or arsenic acid, one of which he represents by 2OV2O-,. 

 P.Ov 6H0O+53 ÏL.O, and he concludes that " these complex iiiorgauic acids form a new 

 department of inorganic chemistry, and not a series of isolated compounds." 



§ 118. "With regard to all such complex species, Gibbs justly remarks, " we have no 

 positive knowledge of the composition of these salts, their molecular weights being, as in 

 the case of most inorganic compounds, entirely unknown." He adds, that the progress of 

 science "tends constantly to show that the structure of inorganic molecules is more com- 

 plex than we formerly supposed," ' and illustrates the great complexity in these com- 

 pounds by a phosphotungstate including vanadium and barium, represented by the for- 

 mula GOAVO,. 3PA- 2VA- VO,. 18BaO + 144H.,0, and having in his opinion " the highest 

 molecular weight yet observed, 200')8." He describes another similar compound, GOWO.i. 

 3PA- "V,0-„ YO,. 18BaO + 1.50H.O, of which he says, " it is almost certainly a double or 

 triple salt, l>\rt still shows how five different oxyds may exist in a single well-defined and 

 beautifully crystallized compound." Besides these soluble and hydrous species, all pro- 

 duced in the moist way, is the curious gold-colored insoluble anhydrous crystalline body 

 discovered by "Wohler, which is formed at a red heat, and is generally described as a 

 tungstate of tuugstous oxyd and soda. This, Gibbs suggests, may possibly be represented 

 by IG'WOa. 4"W02, "TNaO, which corresponds to a unit-weight of 5002. 



' Wolcott Gibbs on Complex Inorganic Acids ; Amer. Jour. Science, 1877, xiv. 61 ; also in abstract Proc. Brit. 

 Assoc. Adv. Science, Montreal, 1884, p. 667, and more fully in Anier. Jour. Cliemistry, 1S70-1S8.% i. 1, 217; ii. 217, 

 281 ; iii. 31 7, 402 ; iv. 377 ; v. 301, .391. 



