The lead should be melted first and then the bismuth, tin and cadmium added in the order named.
Perikon Detector.—The Perikon detector is one of the latest types to come into extensive use. It consists of two crystals, zincite and chalcopyrites,[4] set in cups in the manner just described and placed in contact with each other. The minerals are mounted similar to those in Fig. 105. The zincite should present a rather flat surface with the grain of the crystal parallel to the sides of the cup so that the top surface corresponds to the end of a stick of wood sawed at right angles to the grain. More than one crystal of zincite is usually set in the same cup. The chalcopyrites should present a rather blunt point. The cup containing the chalcopyrites is the smaller and is bored and threaded to fit a thumbscrew which passes through the collar in the spring, S, of the "universal" detector. The bottom of the cup containing the zincite is brightened so as to insure a good contact and then placed on the bed plated under the cup containing the chalcopyrites which is fastened to the thumbscrew. The zincite may then be moved around until the most sensitive portion is found. The chalcopyrites is lowered until it comes into contact with the zincite and then the pressure regulated by means of the large adjusting screw.
Fig. 109. Perikon Detector Elements.
The Perikon detector gives excellent results without a battery and is preferably used in that manner. If a battery is used, a potentiometer to lower the voltage is necessary.
When adjusting this or the carborundum detector where a battery is used, the pressure must be very carefully regulated until it is found to be the best. When the pressure is light the signals in the phones are due to an imperfect contact, and when it is slightly increased the rectifying properties of the crystal are brought into play.
The Perikon detector illustrated in Fig. 110 is somewhat similar to that used for commercial work.
The standards or posts supporting the cups which contain the elements are brass rods 1/2 inch square and 1 1/2 inches high. A hole is bored in the bottom of each and threaded with an 8-32 tap to receive a machine screw which passes through the base and holds them in an upright position. A hole is bored 1 1/8 inches from the bottom, in the face of one standard and threaded with an 8-32 tap. A brass rod 1 1/4 inches long, carrying at one end a cup 1 inch in diameter and 3/8 inch deep, is threaded to fit in the hole in the standard. The zincite is mounted in this cup.
