Probably the most well known form is the electrolytic detector which consists of an exceedingly fine platinum wire dipping into a cup of dilute nitric acid far enough to just touch the surface of the liquid. The telephone receivers are connected to the detector, in series with a battery. The current from the detector causes bubbles to continuously form on the end of the wire and insulate it from the liquid so that the current cannot flow. When the aerial is struck by a wave, the feeble alternating currents break down the bubbles and permit the currents to flow, causing a sound in the telephone receivers.
The detectors in most common use to-day are of the crystal or rectifying type. There are a great many different forms of this type of detector, each one of which possesses certain features making it peculiarly adaptable under certain circumstances.
FIG. 46. Silicon Detector.
The silicon detector consists of a flat surface of highly polished silicon upon which rests a brass point.
The Pyron detector is composed of a crystal of iron pyrites embedded in a cup of fusible metal. A small wire spring bears against the surface of the crystal. The Pyron detector is somewhat harder to adjust than other forms of crystal detector, but remains in a sensitive condition much longer.
FIG. 47. Perikon Detector.
The Perikon detector consists of a cup of fusible alloy in which are imbedded several pieces of a mineral called zincite. Another cup containing a fragment of chalcopyrites or bornite is held in a cup carried on the end of a rotating rod. The chalcopyrites is brought into contact with one of the crystals of zincite and the pressure adjusted by means of a spring. The Perikon detector will operate without a battery, but that latter is necessary in order to obtain the best results when receiving faint or far away signals.
