98 Allen and White — Polymorphic Forms of 



larger quantity. The mass thus formed is scarcely pasty at 

 the highest temperature of an ordinary Bunsen burner, yet the 

 yellow color shows that the silicate is completely permeated by 

 the vanadate. If one desires as large crystals as possible, it is 

 well to take more vanadate and heat for a longer time. To 

 get the silicate in pure condition, it is best to break up the 

 fused mass in a mortar, with a little water, cover it with, say, 

 50 to 100- cc. cold water, and then add a few drops of dilute 

 hydrochloric acid, stirring thoroughly. After a few minutes, 

 pour off the water and repeat the treatment until the water is 

 no longer colored yellow. In this way the calcium vanadate 

 is decomposed and removed more readily than with water 

 alone, while if one keeps the acid cold and very dilute, the sili- 

 cate is not decomposed to any extent, and the microscope 

 shows the product to be unmixed with foreign matter. It 

 consists, as stated above, entirely of wollastonite in beautiful 

 transparent crystals of short prismatic habit, with sliarp edges 

 and well developed faces. The largest were about 0*2 mm long. 



This formation of wollastonite could hardly be anything else 

 than a true reversion. It is well known that such transforma- 

 tions in solid bodies may be facilitated by the use of solvents 

 which probably overcome resistance to molecular movement. 

 In this case, at the temperature of 800 to 900°, wollastonite 

 should be the more stable polymorph, possessing a lower vapor 

 pressure and a lower solubility. Given a nucleus of this form, 

 therefore, the other should pass into solution and continually 

 precipitate in the form of wollastonite. That this is really 

 what happens, we proved hy stopping the transformation 

 before it was complete (5 grams silicate to 1 gram vanadate 

 heated three hours). Large grains of pseudo-wollastonite 

 remained unchanged except for a rounding of corners and 

 edges, and side by side with them appeared small well-formed 

 crystals of wollastonite. 



As these crystals, on account of their freedom from bubbles 

 or pores, seemed especially adapted for the determination of 

 density, two separate preparations were made for this purpose. 



Prep. I. Prep. II. 



Sp. gr. 2-914. Sp. gr. 2-912. 



Analysis. Analysis. Cal. for CaSi0 3 



Si0 2 51-94 52-00 51-86 



CaO 47-69 47-46 48-14 



Fe o 0, etc -19 -18 



Vfi* -38 -49 



* Both preparations had a pale blue tint, which led ns to suspect that the 

 vanadium had been reduced in the process of heating over the gas flame to 

 the blue oxide V2O4. 



