Thallium oxide resembles lead peroxide in color; at a
strong heat it melts, becomes darker, and is converted into peroxide,
in which state it can be weighed.
_Silver._--All solutions of silver salts, except the nitrate, and
those containing a very large quantity of free nitric acid or
nitrates, deposit electrolytically merely metallic silver. In the
above mentioned exceptional cases there is formed a small quantity of
peroxide which adheres to the anode as a blackish-gray deposit. The
greatest quantity of peroxide is obtained on employing a concentrated,
strongly acid solution of the nitrate, and a strong current. If the
solution is very dilute we obtain no peroxide, or mere traces which
disappear again toward the end of the process. The peroxide is
deposited at first in small, dark, shining octahedral crystals;
subsequently, in an amorphous state. At 110 deg. it evolves oxygen
suddenly, and is converted into metallic silver. It dissolves in
ammonia with a violent escape of nitrogen. In nitric acid it dissolves
without decomposition and with a red color.
The author uses a galvanic current for reducing silver residues,
consisting of sulphocyanide. The salt is mixed with sulphuric acid in
a roomy platinum capsule, and a fine platinum wire gauze is used as
positive electrode.
_Bismuth._--The current resolves bismuth solutions into metal and
bismutic acid. The latter is deposited at the positive pole, and in
thin layers appears of a golden-yellow, but in thick strata is darker,
approaching to red.
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