902 
isotropous glass was obtained. However the substance will erystallise 
so easily, that also here some crystalline particles always appear 
to be present. The refractive index of the glass was: np = 1.618 + 
+ 0.002; in the immersion liquid used it produced a beautiful pink 
colour (monochrome-effect). At 25°.2 U. the glass possesses a specific 
weight of: d,.— 3.540; the specific volume thus being greater than 
that of the crystalline substance. On carefully heating the glass 
becomes gradually opaque under transformation into a microcrys- 
talline mass. 
§ 5. Barium-Metasilicate: basi, 
This compound was prepared in a quite analogous way as in the 
case of the strontium-salt. It may be remarked here, that the purest 
bariumsilicates of commerce, e.g. the product of KAHLBAUM, always 
contain an appreciable quantity of water (11 or 12°/,); if this is 
eliminated, the substance appears furthermore never to contain more 
than about 70°/, of BaO, i.e. about 1.8°/, less than corresponds 
with the theoretical composition. Often also some sodium is found 
as an impurity. 
The heated mixtures of the components were melted three times 
at 1650° C., ground, sieved and again melted. The thus obtained 
product, with refractive indices of about 1.666 to 1.669, was 
analysed. The numbers found are : 
Observed : Calculated : 
SiO, - 29,48 °/; 29,44 °/, 2812219 
BaO 10:50 fe 70,53 °/, (ee ftcha A 
In the case of this substance the meltingpoint was determined 
several times with the aid of thermo-element IV. The following 
values were found : 
16799 M.V., with a furnace-gradient of 30 M.V. per min. 
16783 ,, i353 5 5 Ns 26° 5, Sa oe 
16812 „ a >» 
16799 „ OE a 55 ALO iO 
Mean: 16799 M.V. +13 M.V. (uncorr,). 
The correction for this thermoelement at this temperature being 
—8 M.V., the melting-point of this product can be fixed upon : 
16791 M.V. + 13 M.V., corresponding with 603° + 1°C. on the 
nitrogen-gasthermometer. 
Because the substance could not yet be considered as a perfectly 
pure BaSiO,, it was improved by addition of BaCO,, repeatedly 
heated and then analysed. We found the following numbers : 
