c. tube,
whether 1/4 c.c. should be deducted or not.
[Illustration: FIG. 66.]
It is better to add dilute sulphuric acid, and to watch for the
appearance of a precipitate in the test tube, than to add baric chloride
and to look for its non-appearance; besides, baric chloride is much less
likely to be present in a test tube as impurity than sulphates are. In
this way the chance of error from what are termed "accidental causes" is
diminished.
The following experiments show the effect of variation in the conditions
of titration:--
Make _a standard solution of sulphuric acid_ by diluting 43.65 grams of
sulphuric acid (sp. g. 1.6165) to 1 litre: 100 c.c. will contain 1 gram
of sulphur. An equivalent solution may be made by dissolving 100.62
grams of sodium sulphate crystals (Na_{2}SO_{4}.10H_{2}O), or 86.88
grams of ferrous sulphate (FeSO_{4}.7H_{2}O), in water (oxidising the
latter), and diluting to 1 litre.
The order in which these experiments are given is that in which they
were made in an investigation into the conditions under which the
titration could most accurately be effected.
~Effect of Hydrochloric and Nitric Acids.~--The titrations were
performed in the manner already described, but sodic acetate and acetic
acid were absent. Twenty c.c. of the standard solution of sulphuric acid
were used.
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