JOHNS : EXPERIMENTAL PETROLOGY. 
467 
Using 
a solvent : 
a fused mass having the following composition as 
SiO, 
Fed 
Fe,0, 
AI3O; 
MnO 
CaO 
MgO 
53-68 
2004 
1- 86 
4-61 
14-62 
2- 50 
2-58 
Total 99-89 
with some CaO, it was found that silica was soluble in it in 
varying proportions at temperatures below that of the fusion 
point of silica itself. Magnetic oxide was soluble in the original 
silicate, and the surface film, so easily detached in the case 
of pure fused silica, was firmly adherent, and in the cold state 
could be seen to have diffused into the silicate mass for some 
distance. By adding silica in increasing quantities to the original 
silicate, and thus increasing its acidit}^ it was found that its 
power of dissolving magnetic oxide decreased. Solubility was 
therefore, at a temperature somewhat below 1,800° C, in the 
inverse ratio to the aciditj^ 
As the opportunity offers the experiments will be continued, 
using other silicates as solvents and varying the temperature, and 
also using other minerals as solutes. So far as they go the results 
seem to point to the varying solvent power of fused silicates on 
small quantities of minerals, such as magnetite, zircon, &c., 
during a progressive fall of temperature, as being the factor that 
determines their early separation in acid rocks like granite. 
