Dr. Gibbs's Contributions to Analytical Chemistry. 205 
3. The presence of an excess of nitric acid prevents the pre- 
cipitation of the manganese, since, as Crum long since showed, 
ypermanganic acid is formed and remains in solution. 
Tartaric acid and those organic substances which are burned 
at the expense of the peroxyd of lead, do not interfere with the 
precipitation of the manganese. ‘The organic matter is first de- 
stroyed by the oxygen of the peroxyd of lead, and afterward the 
manganese is precipitated by the excess of the peroxyd added. 
When the quantity of organic matter present is large it is always 
better to separate the manganese by means of sulphydrate of 
ammonium in the usual manner. 
5. When, however, oxalic acid is present, we may avoid the 
use either of an inconvenient quantity of peroxyd of lead, or of 
sulphydrate of ammonium, by means of: chlorine or bromine. 
Either ofthese agents readily converts oxalates into carbonates 
by a well known reaction, RO, C203-+Br=RrB+2002. pe 
6. The presence of an excess of free acetic or succinic acid 
does not prevent the complete precipitation of manganese by per- 
oxyd of lead. ‘ 
_7. The same observation applies to the presence of sulphate, 
hitrate, and chlorid of ammonium, and therefore, probably, to all 
ammoniacal salts. 
anes : 
added to the neutral solution of the three bases in ehlorhydnic, 
hitric or sulphuric acid ; the whole is then to be digested upon 
the sandbath for an hour at a temperature of 85° C., care being 
taken to agitate the solution frequently and thoroughly with a 
glass rod. For every gramme of matter analyzed it is well to 
oughly washed with hot water. The’ filtrate contains the alka- 
line bases and lead, but is absolutely free from manganese. 
be separa 
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