EXPERIMENTS 345crystals, and wash them with a little distilled water. Dry them
thoroughly at room temperature with white paper towels. Do
not expose the crystals to direct sunlight or to temperatures higher
than that of the room. Discolored crystals may be washed with
a little distilled water and dried as before.
QUESTIONS- If an unacidified solution of ferrous sulphate is oxidized by
the oxygen of the air, what products are formed? Equation?
Compare the equation for the oxidation of ferrous sulphate as
carried out in this preparation. - Experiment: Prepare a solution of a ferrous salt by dissolv-
ing 2 grams of ferrous ammonium sulphate in 20 cc. of water,
adding a little dilute sulphuric acid and a piece of iron wire.
Test both this solution and a solution of a ferric salt (nitrate or
chloride) with potassium ferrocyanide, potassium ferricyanide, and
potassium sulphocyanate. Tabulate the results. These consti-
tute the standard tests for ferrous and ferric salts. Write equation.
Experiments
The elements of the alkali and alkaline earth families show a
uniform valence in all their compounds. Proceeding in the order
in which the elements have been taken up in this book, a con-
stantly increasing tendency has been shown to display two or
more valences. In fact, the most important chemical properties
of the elements considered in the present chapter depend on their
ability to change their valence. When the valence changes to a
lower one the element acts as an oxidizing agent. Examples of
compounds of chromium and manganese acting as oxidizing agents
are shown in Experiments 10 and 23, pages 164 and 176.- Stability of Carbonates of Metals in Divalent State.
Heat about 1 gram of dry, light green nickel carbonate in a
dry test tube by shaking it a little distance above a small
flame. The powder turns black, and the gas that comes off
clouds a drop of lime water. Treat a second sample of nickel
carbonate with dilute HC1. It dissolves with effervescence to
give an apple green solution; no odor of chlorine is manifest.
Treat the black residue with dilute HC1. It dissolves to give an
apple green solution, and a strong odor of chlorine is manifest-