A very pretty and instructive experiment may be performed by arranging
the apparatus as shown in Fig. 10, with the copper strips, H H,
inserted in clean water and the galvanometer placed in the circuit.
The deflection of the galvanometer needle will be very slight, showing
that the resistance of clean water is considerable. A few drops of
sulphuric acid or even vinegar will increase the conductivity of the
water so as to produce a marked deflection of the galvanometer needle.
Common salt added to the water will produce the same effect.