. Elementary and dental radiography . ent work only a part ofthe condenser is used, with the lever arm on the button marked highfrequency. Second, cut out all the resistance of the rheostat, separate the slidingrod or rods to the maximum spark gap—usually about 6 inches—andturn on the current. Third, widen and narrow the regulating spark gap until the cur- MAKING PliNTAL RADIOGRAPHS 131 rent is as high in milHampcrage as it can be and still jump the terminalspark gap. It will be remembered that widening the regulating sparkgap (up to a certain point) increases the voltage of the output current
. Elementary and dental radiography . ent work only a part ofthe condenser is used, with the lever arm on the button marked highfrequency. Second, cut out all the resistance of the rheostat, separate the slidingrod or rods to the maximum spark gap—usually about 6 inches—andturn on the current. Third, widen and narrow the regulating spark gap until the cur- MAKING PliNTAL RADIOGRAPHS 131 rent is as high in milHampcrage as it can be and still jump the terminalspark gap. It will be remembered that widening the regulating sparkgap (up to a certain point) increases the voltage of the output currentat the expense of the milliamperage, and that narrowing it increases themilliamperage at the expense of the voltage. Alter the regulating sparkgap to get as heavy a spark as possible. It should require but a few sec-onds to accomplish this regulation. Sometimes it is impossible to obtainas fuzzy a spark as you know the machine is capable of giving. This isdue to the fact that the little approximating metal studs at the regulating. Fig. 117. Radiograph by Peabody, of South Orange, N. J. spark gap are dirty. Place a piece of emery cloth between the studs,screw them together until they hold the cloth loosely, then draw thecloth back and forth over the face of the stud. Clean both studs in thisway. Fourth, place a piece of plate glass between the terminals in orderthat a high vacuum tube, one w^ith a resistance equivalent to 6 or moreinches of parallel spark, may be used. Fifth, connect the tube to the coil, set the tube-regulating spark forabout 5 inches, turn on the current and see that the tube lights up O. K. I recall and shall here set forth an experienceJin TnstructlPC I ^lad while making a radiograph on a large plate experience. with a small, high-frequency C(^il. I had followed the technic given above, posed my patient, andturned on the current for a one-minute exposure. For the first thirty-five seconds the tube maintained a good light. Then suddenly the cur-rent cease
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