Components of an Igneous Rock — Williams 37 
SiO= 72.26 per cent. 
APO' 13 . 58 per cent. 
Fe'O^ 2.97 per cent. 
FeO 0.75 per cent. 
MgO . 034 per cent. 
CaO 1.24 per cent. 
Na^O 2.18 per cent. 
K'O 5 . 69 per cent. 
H^0+ . 57 per cent. 
H^O — 0.09 per cent. 
99.364 
Calculation from this analysis yields the following ap- 
proximate mineral composition : 
Quartz 35.90 percent. Biotite 0.255 percent. 
Orthoclase 34 . 48 per cent. R^agnetite 2 . 605 per cent. 
Albite 18.74 per cent. Hematite 1 . 10 per cent. 
Anorthite 6.25 per cent. ffO-t- . 095 per cent. 
H'O— . 577 per cent. 
Total 100.002 per cent. 
The small amount of biotite, which would not result 
directly in calculating the norm, it was found convenient 
to bring in to take care of a small excess of alumina and 
the little MgO that appears in the analysis. Inspection of 
these results shows a total feldspar percentage of 5947 of 
which 24.99 is plagioclase. The total for those minerals, 
viz., biotite, magnetite and hematite, which, in both micro- 
scopic and heavy solution analysis, are grouped as "iron 
ores," is here 3.96 per cent. 
(b). HEAVY SOLUTION METHOD 
Thoulet's* solution was used in the present experiments. 
It is made by dissolving in cold water potassium and mer- 
curic iodide, KI and Hgl", in the ratio i : 1.24. This gives 
a clear greenish-yellow liquid, the depth of color depending 
on the degree of concentration. Moderate heating does 
not afifect it, so that its density can be increased or dimin- 
ished to any desired point. 
A description of the apparatus employed in making 
separations may be found in Rosenbusch's work.i" The one 
*For details regarding this solution, see H. Rosenbusch's Mikrosco- 
pische Physiographie, ed. 1892, pp. 231-235; and the Englisli Translation 
by Iddings, pp. lOO-lOL 
'fSee also W. J. Sollas, Contributions to a Knowledge of the 
Granites of Leinster, Trans. Royal Irish Acad. Vol. xxix. pt. xiv. 
p. 427. 
