When the amount of
manganese is small, the separation of the two elements takes place very
rapidly, and the results are accurate. If the amount of manganese is
more than double that of iron, the separation of the latter will take a
much longer time. Then, in order to effect a complete separation of the
two elements, it is necessary to redissolve the deposited manganese in
oxalic acid (the acid is added, without interrupting the current, until
the liquid becomes red), and the current is allowed to continue its
action.
It was found desirable, in effecting this separation, not to employ
too strong a current (two Bunsen elements will suffice), and only
to increase the strength of the current when it is necessary, in
consequence of a large amount of manganese being present, to redissolve
the peroxide.
When the process is completed, it is not advisable to allow the current
to act any longer, for otherwise some of the peroxide may adhere firmly
to the iron, and the latter (after previously having poured off the
liquid) must be redissolved in oxalic acid, that is to say, the
electrolysis must be repeated. As has been already mentioned in the
determination of manganese as peroxide, its precipitation from ammonium
oxalate is not complete. The solution which contains the greater portion
of manganese, suspended as peroxide, must first, therefore, be boiled to
decompose the ammonium carbonate; the remainder of the ammonium oxalate
is neutralized with nitric acid, and the manganese converted into the
sulphide by ammonium sulphide.
Pages:
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124