Zinc possesses some peculiar property which makes it very efficient for a spark-gap, and for this reason the electrodes of a spark-gap are usually zinc.
Fig. 222.—Small Spark Gaps.
The figure shows two different forms of electrodes. In one, they are made of zinc rods and provided with “electrose” handles. In the other gap, the zinc electrodes are in the shape of "tips" fitted on the ends of two short brass rods.
A one-inch spark coil will give very good results by connecting the spark-gap directly across the secondary of the coils. The aerial is connected to one side of the gap and the ground to the other.
The transmitter may be "tuned" and the range sometimes increased by using a condenser and a helix.
A condenser is most easily made by coating the inside and outside of a test-tube with tinfoil so as to form a miniature Leyden jar. The end of the tube is closed with a cork through which passes a brass rod connecting to the inner coating of tinfoil.
Fig. 223.—Diagram showing how to connect a Simple Transmitter.
If such a condenser is connected directly across the spark-gap, the spark will become very white and crackling.