Five
milligrams of silver in solution (5 c.c.) is then added, and the assay
proceeded with in the usual way; 5 milligrams of silver being deducted
from the amount found.
There is required for the assay a _standard solution of sodium
chloride_, which is prepared by dissolving 5.4162 grams of the salt
(made by neutralizing carbonate of soda with hydrochloric acid) in water
and diluting to one litre. 100 c.c. of this is equivalent to 1 gram of
silver.
The weaker solution of salt is made by diluting 100 c.c. of the stronger
one to one litre. One c.c. of this will equal 1 milligram of silver, or
0.1 c.c. of the stronger solution.
A _standard solution of silver_ equivalent to the dilute salt solution
is made by dissolving 1 gram of fine silver in 10 c.c. of dilute nitric
acid, and diluting with water to one litre.
[Illustration: FIG. 44.]
The solution of salt is standardised as follows:--Weigh up 1.003 gram of
fine silver and dissolve in 25 c.c. of dilute nitric acid in a bottle
provided with a well-fitting flat-headed stopper. Heat on the water bath
to assist solution, resting the bottle in an inclined position. When
dissolved blow out the nitrous fumes with the help of a glass tube bent
at right angles. Run in from a stoppered pipette (as shown in fig. 44)
100 c.c. of the standard salt solution, and shake vigorously until the
solution clears.
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