NEW CRYSTAL DETECTORS.
Silicon Detector.—The silicon detector is always interesting because it was one of the first mineral rectifiers to come into extended use. The photograph shown below illustrates one of the latest forms of the silicon detector.
Fig. 162. Silicon Detector.
The large cup supported by the left-hand standard contacts several pieces of fused silicon embedded in fusible alloy. The right-hand standard supports a movable "offset" cup the same as that used on the Perikon type of Detector. A small piece of arsenic is mounted in this cup and may be brought to bear against any portion of any of the silicon crystals.
Pyron Detector.—The Pyron detector is not new, but the photograph shows a very simple and efficient form in which a fine wire is brought to bear against a crystal of iron pyrites mounted in a small cup.
Fig. 163. Pyron Detector.
Galena Detector.—Although galena is named in the list of sensitive minerals on page 132 it has come into such extensive use as a detector since the first edition of this book to be worthy of special attention. Galena detectors are often spoken of as "cat-whisker" detectors because of the long fine wire used to secure a delicate contact with the mineral.
The mineral is usually placed in a cup and held in position by imbedding in fusible alloy or clamped with a set screw. The best surface of the mineral should be selected by testing previous to imbedding it in the cup. Contact is made with the surface of the mineral by means of a piece of No. 30 phosphor bronze wire mounted on the end of a short brass rod fitted with an adjusting screw so that by turning or twisting the surface of the mineral may be "searched" and the tension varied.