208 
IOWA ACADEMY OF SCIENCE 
When the specimen of argillaceous limestone was first sent out 
for the co-operative analysis, about two and one-half years ago, 
we experienced no difficulty in obtaining 1 18% of silica, all that it 
contains, by a single evaporation. The specimen seems to have 
undergone a change and in recent months it has been impossible 
to secure all the silica even by two or three evaporations. We 
have been obliged to follow the method of Hillebrand 2 and seek 
for three or four per cent of the silica in the iron and aluminum 
precipitates. These are fused with acid potassium sulphate, and 
afterwards digested with sulphuric acid and heated until fumes 
are given off. When the silica in the specimen amounts to only 
a few per cent, the portion that persists in solution is necessarily 
small. It is usually greater when the silica is determined by an 
alkaline fusion. 
THE EFFECT OF DIFFERENT ACIDS AS SOLVENTS. 
Dolomite rock, and ores of iron and manganese were treated 
with different acids as solvents and the resulting insoluble residue 
was investigated. In some cases the nature of the residue other 
than the silica was examined. Each specimen studied was finely 
ground with agate mortar and pestle until the powder did not 
feel gritty when placed between the teeth, and it was then thor- 
oughly mixed. About one gram of the powder was used in each 
determination. 
SIDERITE. 
(a) A gram of the powder was dissolved in pure dilute hydro- 
chloric acid, and the insoluble residue at once filtered off. This 
was found to be 6.06%. When treated in the platinum crucible 
with sulphuric and hydrofluoric acids, the loss of weight represent- 
ing the silica was 1.44%. A blank test was made of the sulphuric 
and hydrofluoric acids and no residue was left on their evaporation. 
No residue was obtained by evaporating the filtrate from the in- 
soluble residue. 
(b) A portion of the powder evaporated in a porcelain dish 
on the water bath and stirred to a fine, dry powder gave an insol- 
uble residue of 6.07%. The treatment of this with hydrofluoric 
and sulphuric acids showed that 1.45% of silica was present. The 
residue in the crucible which had the appearance of iron was dis- 
1. Chem. News 92.61, Aug. 11, 1905. 
2. Journ. Am. Chem. Soc., Nov 1903. 
