LECTURE DEMONSTRATION O F X-RAYS AND CATHODE RAYS CHARLES L. CHRIST
Wesleyon Uniuersity, Middletown, Connecticut
ALTHOUGH it is generally realized that well- tial of 80,000 volts and a current of 1 milliampere, the planned demonstrations of the production and proper- high voltage and current being controlled by means of ties of cathode rays and X-rays lend very effective aid an auto-transformer and a resistance, respectively, to the teaching of these subjects, many institutions connected in the primary circuit and housed in a control have had to forego these because of the prohibitive cost stand. The high tension lines may be carried safely by of the necessary apparatus. Such equipment, consist- clean wooden funnel supports, as shown. ing of an induction coil, X-ray tube, Crookes tubes, In this setup the Coolidge tube plays a dual role. It magnet and fluoroscope, all designed specifically for is used both for the production of X-rays and as a valve demonstration purposes, and obtained from the labora- tube for the rectification of the electron beams produced tory supply houses costs a t least $250. in the Crookes tubes. It was found that the electron To meet this difficulty, we have taken advantage of beams produced in this way were much sharper than the fact that obsolete X-ray medical equipment may be those produced through the use of an induction coil. obtained from X-ray dealers a t prices appreciably less In the X-ray experiments a square of Patterson Type B than that asked for new standard demonstration appa- fluorescent screen serves very well as a fluoroscope. ratus. The apparatus described below is, with the ex- Experiments showing the charge and the kinetic energy ception of the two Crookes tubes (low cost items), com- of the electron beams are carried out in the usual way.' posed entirely of such inexpensive obsolete pieces. I t It is a pleasure for the author to acknowledge his has been found to give highly satisfactory results. indebtedness to Mr. J. W. Moulton of the General The figure shows the setup, consisting of two Crookes Electric X-ray Corporation. Thanks are also due to tubes and a Coolidge type X-ray tube in series. The Dr. M. G. Burford, of this laboratory, for the photothree tubes are energized as a unit by a high-voltage graph used in this paper. oil-immersed transformer, which contains a built-in filament transformer for lighting the filament of the 1 ARTWR, "Lecture demonstrations in general chemistry," Coolidge tube. The apparatus is operated a t a poten- McGrsw-Hill Book Company, New York, 1939, p. 237.
