867 



Li,SiO„ can be indicated thus at 11944 ± 12 M. V. or 1201° C. 

 + 1°. The nieltingpoint can be localised so sharply on the heating- 

 curves, that the coniponnd can be used vvitli success for calibration 

 purposes; the temperatuie of equilibrium is here really ^dependent 

 of the speed of healing-, in very wide limits. 



Uy means of the method of immersion, the retractive indices for 

 sodiumlight were determined on : 



;?x> = 1,609 + 0,004, for vibrations parallel to the direction ot 

 elongation of the needles, 



nj) :r= 1^584 + 0.002, for vibrations, orientated perpendicularly 

 to the first direction. 



The birefringence is strong and of positive character, l)eing about 

 0,025. The specific gravity at 25° C. was : d, = 2,520. Tn fig. 2 

 a microjihotograph of the crystallized nieta-silicate between crossed 

 nicols is given while this is immersed in a liquid of about (he same 

 refractive index. 



With the aid of the method of quenching, used in this laboratory 

 with substances, heated at a constant temperature during a long 

 time, we were able to ger some glass of the metasilicate. As the 

 compound crystallizes extraordinarily rapidly, it was only possible to 

 succeed by using very small quantities of the silicate, about 0,05 

 to 0,1 gram, wrapped in platinum-folium, and suddenly chilling 

 them by means of cold mercury. The refractive index of this glass was 

 found to be : nn - 1,548 Hi 0,002 at 25° C; thus it appears to be 

 appreciably less than the smallest index of the crystallised substance. 

 The specific gravity of the glass was determined at : d^ = 2,330, thus 

 being at 25° C. also much lower than for the crystallized substance. 



§ 7. We found no indication whatever of an inversion tempera- 

 ture in heating and cooling our preparation; also in the microscopical 

 work we were not able to find any other modification of the meta- 

 silicate than the one just described. 



However G. Friedel ^) described in 1901 another form of lithi- 

 ummetasilicate, which he claimed to be trigonal and, strangely enough, 

 to be homeomorphous with phenakite. He obtained this form ot' Li^SiO^ 

 by heating the product, obtained by the reaction between Li.JJ, 

 SiO^, and rauscovite in solution at 540° C under pressure. His 

 results do not agree with those of Margottet and Haltefeuilek -), 

 who used LiSi as a flux, and obtained needles, to which they 

 attribute rhombic symmetry, with [)seudo-hexagonal character. 



n G. Friedel, Bull, de la Soc. Miner, dc France. 24, 147 (1901). 



-) Hautefeuille and Margottet, ibid. 4, 241 (1881); Gompl. leud., loco cit. 



