206 
IOWA ACADEMY OF SCIENCE 
finely pulverized. After dissolving the fused mass, the boric 
oxide is completely volatilized with methyl chloride. An advan- 
tage of this and the lead oxide method is that they do not introduce 
alkalies into the substance to be analyzed. 
FUSION WITH BISMUTH SUBNITRATE. 
Hempel and Koch have obtained satisfactory results by fusing 
with bismuth subnitrate. A half gram of the powdered silicate is 
fused with ten grams of the subnitrate. On diluting the filtrate 
from the Si0 2 with water, a greater part of the bismuth is pre- 
cipitated as oxychloride, and the remainder is afterwards removed 
with sulphuretted hydrogen. A silicate can also be fused with 
borax. It must, nevertheless, be said that the different fluxes 
mentioned, with the exception of the alkaline carbonates, will an- 
swer in certain cases, but they are not of universal application. 
SOME EXPERIMENTS IN ESTIMATING SILICA. 
1. The Niagara dolomites of Eastern Iowa. 
The silica was determined by two methods : 
(a) A gram of the finely powdered rock was placed in a small 
beaker, and covered with a watch glass, a small quantity of hydro- 
chloric acid was added, and the carbonates were dissolved by care- 
fully heating to the boiling point. The insoluble portion was fil- 
tered off and its weight determined. 
(b) A gram of the powder was dissolved in a porcelain evap- 
orating dish, evaporated and stirred to a fine powder, and treated 
with hydrochloric acid and water in the usual way. The insoluble 
residue was finally filtered and weighed. The results of the two 
methods are as follows: 
(a) .78% Si0 2 (b) .75% 
.76% Si0 2 I .73% 
.81% Si0 2 .85% 
.87% Si0 2 .87% 
The residues were tested with sulphuric and hydrochloric acids 
and found to be practically pure silica. Most of the layers of this 
rock in the vicinity of Mount Vernon will leave a residue on treat- 
ment with the sulphuric and hydrochloric acids. The insoluble 
residue from hydrochloric acid in this particular layer must have 
been grains of fine, pure sand, or pure quartz crystals. 
In the various layers of the rock which we have studied, whether 
the insoluble residue is pure silica or not, the treatment described 
