. Dental and oral radiography; a textbook for students and practitioners of dentistry . ching the negativewire directly to the regulating chamber and passing asmall amount of current through the circuit. These manipulations should be carried out with the 112 DENTAL AND ORAL RADIOGRAPHY greatest caution, for a tube is an extremely delicate andsensitive piece of apparatus and ivill not stand careless operator can quite easily reduce the vac-uum to such a degree that the tube is useless. Such atube has a purple appearance when the current is passedthrough it. If such a tube has not been t
. Dental and oral radiography; a textbook for students and practitioners of dentistry . ching the negativewire directly to the regulating chamber and passing asmall amount of current through the circuit. These manipulations should be carried out with the 112 DENTAL AND ORAL RADIOGRAPHY greatest caution, for a tube is an extremely delicate andsensitive piece of apparatus and ivill not stand careless operator can quite easily reduce the vac-uum to such a degree that the tube is useless. Such atube has a purple appearance when the current is passedthrough it. If such a tube has not been too greatlyabused, it will often regain its vacuum if given a rest. Ifthis does not bring the vacuum up, it can often be broughtback in the following way: The spiral spring (Fig. 59)connecting the anode and assistant anode should be re-moved and the positive wire from the machine attached A—Anode. U--Assistant Anode C—Cathode r-RegulaiinB Ad-juster G—Hemispluie H-Conneclion WireI-Assistani AnodeCap K-Anode fa|. l^Cathode Call M—Cathode Stream N-Focal Ioint. Fig. 59. to the assistant anode (/). The negative wire is at-tached as usual (at L) and a light current is run throughthe tube for a minute or two at a time. If this is doneonce or twice a day for several days, the vacuum willusually come up. Any increase in vacuum will be indi-cated by the milliampere readings dropping off, or bythe increased length of spark gap the tube will back up. If a tube does not respond to this treatment but con-tinues to be purple while operating, it indicates that itis practically nonvacuous or punctured. It is thenuseless and should be sent back to the manufacturer for DENTAL AND ORAL RADIOGRAPHY TECHNIC 113 repairs. In the event a tnhe is completely punctured,the current in passing through it simply jumps the gap])etween the anode and cathode, and is evident as a lineof white sparks. One tube complication not yet mentioned is sometimesencountered in the use of inductio
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