Platinum is necessary because the sparking would soon corrode other metals, but it is very expensive. To test for platinum put a tiny drop of nitric acid on the suspected metal. If bubbles or smoke appear it is not platinum. After applying this test in any case however, carefully wash off and remove all traces of the acid, as it will corrode the metal into which the platinum is riveted.
Dirty contacts will decrease the current in the bell coils and it will not work well, if at all.
Loose contact screws and wires also give trouble. The adjusting of the contact screw is of the utmost importance, and should never be attempted unless it is clearly necessary.
Faults in Line.
In looking for a fault in a bell circuit make sure the battery is working; if only one or two cells, put the ends of two wires attached to the terminals on the tongue: a metallic taste will indicate current.
Then see that the circuit wires are firmly clamped in the terminals and no dirt or corrosion on the connections.
Next examine the push button and see that the wire connections at the springs are perfect.
If there is no movement of the bell at all when the push is pressed in, take a pocket knife or screw driver, and touch the blade across the push springs. If there is current flowing sparks will be seen when the blade breaks contact between the springs. If there are no sparks, detach the wires from the bell and twist the bare ends together. Then try again for sparks—they may now be very minute. The tongue test is good here.
If current is detected, examine the bell for the defects first mentioned.
But if no current is found at the push now the wires are broken somewhere.