Ammonic nitrate added 1 gram 5 grams 10 grams 20 grams
Cyanide required 21.2 c.c. 22.1 c.c. 23.1 c.c. 24.1 c.c.
These show that combined ammonia seriously affects the titration, and
that the principle sometimes recommended of neutralising the acid with
ammonia, and then adding a constant quantity of ammonia, is not a good
one, because there is then an interference both by the ammonia and by
the variable quantity of ammonic salts.
The same quantity of combined ammonia has the same effect, whether it is
present as sulphate, nitrate, chloride, or acetate, as the following
experiments show. Four lots of 20 c.c. of "copper nitrate" were taken,
and 20 c.c. of dilute ammonia added to each. These were carefully
neutralised with the respective acids, rendered alkaline with 30 c.c.
more of ammonia, cooled, diluted to bulk, and titrated. The results
were:--
With sulphuric acid 22.5 c.c. of cyanide
" nitric acid 22.6 " "
" hydrochloric acid 22.6 " "
" acetic acid 22.5 " "
~Effect of Foreign Salts.~--Sulphates, nitrates and chlorides of sodium
or potassium have no action, whilst the hydrates, carbonates,
bicarbonates, sulphites, and nitrites have an important effect. The
interference of ammonic salts has already been shown.
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