Day and Shepherd — Lime-Silica Series of Minerals. 283 



cooled specimen plunged from white heat into mercury, disin- 

 tegration is immediate. This phenomenon was further veri- 

 fied by fusing the material and dropping it into a furnace held 

 at about 1200° C. After a few moments the charge was then 

 removed and quickly plunged into mercury. Treated in this 

 way, all of a goes over into /?, which in turn will disintegrate 

 completely with little or no delay after reaching the /3 ^ > y 

 inversion temperature. One will sometimes get the a-form 

 by slow cooling, but never the /3-form. 



The 7-form of the orthosilicate crystallizes in the monoclinic 

 system. Its density, determined in turpentine, by the pic- 

 nometer method, is 



2-973 

 2975 



Mean, 2-974 



The difference in volume between the 7 and a or ft forms is 

 therefore nearly 10 per cent, and since the a and particularly 

 the /3-form goes over into the 7 at low temperatures with the 

 greatest readiness, the disintegration of the fused orthosilicate 

 is readily explained. 



Neighboring mixtures containing the orthosilicate as a com- 

 ponent disintegrate beginning with compositions containing 

 only 51 per cent of lime. The disintegration of this prepara- 

 tion is, however, very slow, and usually does not take place at 

 all unless the mixture has been held for some time at a rela- 

 tively high temperature. The 54 per cent mixture can also be 

 readily obtained without disintegration, but with more than 

 54 per cent of CaO, disintegration always occurs under the 

 ordinary conditions of preparation. 



If the orthosilicate be heated to temperatures only slightly 

 above QR (fig. 3) so as to produce the j8-form without sinter- 

 ing, disintegration does not appear on cooling for the reason 

 that the change in volume is not apparent in the powdered 

 material. If the charge be heated to about 1400°, or above 

 1410° where the a modification appears, it sinters tightly 

 together and the disintegration phenomenon is again observed. 

 Charges sintered together at 1400° to 1500° and held continu- 

 ously at any temperature above QR do not disintegrate so 

 long as this temperature is maintained, but as soon as the 

 temperature drops below QR, disintegration recurs, but not 

 at a constant temperature nor at any characteristic rate, the 

 change being very dependent upon the conditions obtaining 

 at the time. 



The orthosilicate is easily attacked by water, giving an alkaline 

 reaction, even when the water is cold, while with boiling water 



