. Dental and oral radiography : a textbook for students and practitioners of dentistry . be, shown in Fig. 27, is radically dif-ferent in design from the other tubes already described,and is different in operation, in that it is energized bytwo independent currents, one of high voltage, and theother of low voltage. For this reason, certain auxiliary REQUISITES OF DENTAL X-RAY LABORATORY 69 apparatus must be used with it, in addition to the hightension current generator. This auxiliary apparatusconsists of a loiv voltage transformer and regulator, andan insulated stand or shelf for holding the
. Dental and oral radiography : a textbook for students and practitioners of dentistry . be, shown in Fig. 27, is radically dif-ferent in design from the other tubes already described,and is different in operation, in that it is energized bytwo independent currents, one of high voltage, and theother of low voltage. For this reason, certain auxiliary REQUISITES OF DENTAL X-RAY LABORATORY 69 apparatus must be used with it, in addition to the hightension current generator. This auxiliary apparatusconsists of a loiv voltage transformer and regulator, andan insulated stand or shelf for holding the transformer,and an ammeter. The low voltage current serves thepurpose of heating electrically a spiral filament of flat,closely wound tungsten wire located within a cylinder onthe cathode. This electrically heated filament serves theimportant function of controlling the milliamperage ofthe current passing through the tube. The higher thefilament temperature, the larger the number of milliam-peres can be made to pass through the tube and hence theshorter will be the exposure Fig. 27.—The Coolidge x-ray tube. This tube is fast becoming popular, due to the fact thatit is rugged of construction, will stand hard and continu-ous service, and because of its ease of control, will giveuniform results. It is safe to assert that its adventmarked the most distinct advance in the field of roent-genology of recent years. A discussion of its use in ourwork will be continued later in Chapter VII. Tube Stand The tube stand, which serves the purpose of holdingthe tube, should be sufficiently heavy to support it againstmotion and vibration, and should be sufficiently adjust- 70 DENTAL AND ORAL EADTOGRATII Y
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