c. of nitric acid diluted with water. Leave the
apparatus in the balance-box for a few minutes and weigh. Introduce into
the flask (through A) about 1 gram of the powdered substance and again
weigh to find the exact amount added. Allow the acid to run gradually on
to the carbonate, and when solution is complete, heat and aspirate. Cool
and again weigh; the loss in weight is the carbonic acid.
For _Example_:--
Weight of apparatus and acids 85.494 grams
" " marble 86.879 "
------
Equal to marble taken 1.385 "
Weight of apparatus and marble 86.879 grams
" " minus carbonic acid 86.2692 "
-------
Equal to carbonic acid 0.6098 "
1.385 : 100 :: 0.6098 : _x_
_x_ = 44.03 per cent.
The substance contains 44.03 per cent. of carbonic acid; a duplicate
experiment gave 43.73 per cent.
This method is quicker, but less exact, than the direct gravimetric
determination.
VOLUMETRIC METHOD.
This, which is of somewhat limited application, is based upon the
determination of the quantity of acid required to decompose the
carbonate. It consists in adding to a weighed quantity of the mineral a
known amount of standard solution of acid which is in excess of that
required to effect the decomposition.
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