388 K T. Allen, F. K Wright and J. K. Clement— 



may be decomposed with hydrochloric acid, so that we expected 

 to be able to remove the excess of reagent from the silicate 

 without difficulty. The silicate and tellurite were therefore 

 mixed in about equal quantities (about 5 grams of each) and 

 heated in a covered platinum crucible by means of a resistance 

 furnace to prevent reduction of the tellurite. At 1000°-1100° 

 some monoclinic pyroxene was obtained, but the greater part 

 of the product proved to be fosterite, formed by "the decom- 

 position of the tellurite and the volatilization of tellurous acid, 

 which partly condensed on the cooler parts of the furnace. 

 The equations : 



MgTeO s + SiO a = TeO s + MgSiO,. 



2MgTeO, + tSi0 2 = 2Te0 2 + Mg 2 SiG 4 . 



represent these reactions. The crystals obtained by this 

 method are not well formed and it is difficult to remove the 

 tellurium completely. 



The above reaction led us to believe that magnesium silicate 

 might perhaps crystallize from molten tellurous oxide, but, 

 though well developed monoclinic prismatic crystals were occa- 

 sionally obtained, most of the silicate was apparently decom- 

 posed by this method. 



With Magnesium Vanadate. — In some earlier experiments 

 on wollastonite carried out in this laboratory,* it was found 

 that calcium silicate could be readily dissolved and recrystal- 

 lized from molten calcium vanadate, the excess of which could 

 be easily removed by alternate treatment with very dilute 

 hydrochloric acid and ammonia ; we therefore expected to be 

 more successful with magnesium vanadate than with tellurite. 

 The conditions followed in the beginning were similar to those 

 which had worked so well with calcium silicate, but as the first 

 results were not satisfactory, we eventually tried various pro- 

 portions of silicate and vanadate at temperatures ranging 

 from 800° to 1050°. At the lower temperature monoclinic 

 crystals of rather poor development were obtained, but at the 

 higher temperature a good deal of fosterite always accom- 

 panied it, and vanadic anhyride was evidently set free, as the 

 product was colored a dark brown. Most of the vanadate 

 and vanadic acid can be removed by cold dilute hydrochloric 

 acid and hot concentrated ammonia, but several per cent are 

 generally retained by the silicate. 



With Calcium Vanadate. — In spite of our apprehension of 



double decomposition with salts containing no common ion, 



we found that calcium vanadate dissolved and crystallized 



magnesium silicate unchanged in composition and sufficiently 



* Allen, White and Wright, this Journal (4), xxi, 97, 1906. 



