M. Scheibler on the Tungstates. 375 



Tungstate of Soda, 3NaO, 7W0 3 + 16 Aq, crystallized in the 

 cold, and 3NaO, 7W0 3 + 14Aq, crystallized in the water-bath, 

 forms beautiful large monoclinic prisms. 



Tungstate of Potass, 3KO, 7W0 3 + 6Aq, crystallizes in small, 

 difficultly soluble, scaly crystals. 



Tungstate ofLithia, 3LiO, 7W0 3 + 16Aq, crystallizes in easily 

 soluble, very beautiful large monoclinic prisms. 



Metatungstates. — The only salt of this class hitherto described 

 is the ammonia salt discovered by Margueritte. 



The solutions of these salts are not decomposed by acids with 

 separation of a yellow or white hydrate of tungstic acid. The 

 metatungstates are formed from the tungstates by adding a 

 strong acid to their solutions as long as the precipitate redissolves, 

 — or better still, by continuously boiling the tungstates with an 

 excess of hydrate of tungstic acid. This hydrate is obtained by 

 the double decomposition of tungstate of soda with chloride of 

 calcium, and digesting the precipitate which is formed with 

 hydrochloric acid. 



The metatungstates are very soluble, and crystallize only when 

 the solution is very concentrated. The alkaline salts crystallize 

 in octahedra. The ammonia salt melts in water like phos- 

 phorus ; its solution is strongly refracting. Its formula is NH 4 0, 

 4W0 3 + 9Aq. The potash and soda salts are similar. On 

 mixing a warm concentrated solution of metatungstate of 

 ammonia with solution of chloride of barium, no precipitate is 

 formed, but on cooling there is deposited 



Metatungstate of Baryta, BaO, 4W0 3 -f 9 Aq. — It crystallizes in 

 large fatty crystals, which are a combination of the octahedron 

 with the prism. The crystals have a considerable specific 

 gravity, and are readily soluble in hot water. 



When a warm concentrated solution of metatungstate of 

 baryta is treated with an equivalent quantity of sulphuric acid, 

 the liquor, after filtration from the sulphate of baryta, deposits, 

 on evaporation in vacuo, small quadratic octahedra of meta- 

 tungstic acid, which apparently have the composition 2HO, 

 4W0 3 + 7Aq. It is a strong acid, and expels nitric and hydro- 

 chloric acid from their combinations. Its solution can be boiled 

 for some time without change, and can be evaporated to the con- 

 sistence of syrup in the water-bath ; but if it be further concen- 

 trated, it passes into the insoluble modification. 



Metatungstic acid is an admirable reagent for nitrogenous 

 bases, which are all precipitated by it in white flakes ; it exceeds 

 phosphomolybdic acid in delicacy. Acid solutions which only 

 contain 2 00 1 000 of quinine or strychnine are made distinctly turbid, 

 and after twenty-four hours small flakes are deposited on the 

 bottom of the vessel. The free metatungstic acid itself is not 



