Ordinary samples are not
sufficiently accurate to allow the use of this method.
The methods of reducing with iron and titrating this with chromate of
potassa, etc., have given a constant average of from 98.60-99.01. These
results are fair, but hard to obtain expeditiously.
Of the methods of precipitating the compounds of the protoxide and
estimating the acid, that of the phosphate is by far the most accurate,
titrating with uranium solution; 99.82 is a nearly constant average
with me, much depending on the operator's familiarity with the uranium
process.
The methods of Lenssen, or ferricyanide of potassium method, yields very
widely differing results. I have found the figures of Fresenius about
the same as my own in this case; that is from 98.00-100.10.
B.--On the Separation. First, from its soluble simple combinations with
the acids or bases containing no iron or cobalt; if they are present, it
is treated as is noted later. If sulphuric acid is present it must be
separated by treating the solution of the compound with barium chloride
and filtering. A nearly neutral solution is prepared in water or
hydrochloric acid and placed in a flask.
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