ELECTRICAL CONDUCTIVITY OF SOLUTIONS 83A careful study of the laboratory experiments and a working
out of the problems in the following sections should give one an
understanding of the theory of ionization, a theory which is of the
greatest service in interpreting the chemistry of solutions. Al-
though the experiments are printed consecutively in one section
and the problems in the next, the two sections should be studied
together.
Experiments- Osmotic Pressure. The formation of osmotic membranes,
as well as the existence of osmotic pressure, may be qualitatively
shown by what may be called the mineral garden, prepared as
follows: small lumps or crystals of certain very soluble salts, such
as ferric chloride, copper chloride, nickel nitrate, cobalt chloride,
and manganese sulphate, are dropped into 50 cc. of a solution of
sodium silicate, or water glass (sp. gr. 1.1), in a small beaker.
The success of the experiment depends on using small, distinct
fragments of the salts. Their behavior resembles that of grow-
ing seeds, as they appear to sprout immediately and to send up
shoots toward the surface of the liquid, which grow with a visible
rapidity.
Record this experiment in the note book, giving a description
and an explanation in your own words. Wash the beaker im-
mediately after the experiment, as the sodium silicate solution
will etch the glass.
ELECTRICAL CONDUCTIVITY OF SUBSTANCES IN SOLUTION
Use the conductivity apparatus found on the ends of the desks, a
diagram of which is given in Fig. 17.
Electrodes A consist of copper rods set so that they will pass into
the two arms of a U-tube when it is raised from underneath. A
lamp of high wattage should be used with these electrodes, which
are designed to show differences in conductivity among good
conductors.
Electrodes B consist of fine platinum wires supported upon glass
rods, and are to be used with a lamp of about 15 watts. They
are to be used in testing the conductivity of solutions of weak
electrolytes in a 3-inch vial. This vial may be raised until the
electrodes are immersed in the liquid. Before testing the conduc-
tivity of any given solution rinse the platinum electrodes with