. Radiography, X-ray therapeutics and radium therapy . wire should beplaced well back from the cathode—say, at a distance of 6 or 7 point is emphasised in another portion of this work. There are exceptions to this rule in the manipulationof those tubes which work best with the regulator at a fixed distance fromthe cathode, according to the hardness of the particular tube and thepurpose for which it is being used. The current may now be switched on, starting with all resistance in,and gradually cutting this out until the tube fluoresces brightly and the tube is inclined t
. Radiography, X-ray therapeutics and radium therapy . wire should beplaced well back from the cathode—say, at a distance of 6 or 7 point is emphasised in another portion of this work. There are exceptions to this rule in the manipulationof those tubes which work best with the regulator at a fixed distance fromthe cathode, according to the hardness of the particular tube and thepurpose for which it is being used. The current may now be switched on, starting with all resistance in,and gradually cutting this out until the tube fluoresces brightly and the tube is inclined to spark over, bring the regulator to within adistance of 4 or 5 inches of the cathode, so as to provide a kind of safety-valve action. This will allow of the sparks passing between the regulatorrod and the cathode, and tend to reduce the vacuum of the tube and so avoidthe tube becoming punctured. Before deciding that a tube needs regulation, allow it to run for a minuteor two to give it an opportunity of finding its balance. Often it will be found. Fig. 39. -Connection of the X-ray tubes to tube on positive pole. 44 RADIOGRAPHY that a tube so treated will settle down after a short run. In other words,do not be in too great a hurry to regulate the tube. A little more or a littleless current passing for a short time may successfully regulate the vacuumand allow of good work being done. If regulation is necessary, proceed to adjust the regulating rod at adistance which will allow sparks to pass between the rod and the cathodeuntil the tube works smoothly, and then remove the regulating rod awayfrom the cathode and test the tube again. Hardening the tube can only be satisfactorily done by gradually workinga soft tube up through using it for very light work or for light treatmentuntil it attains the necessary degree of hardness. Hardening by meansof reversing the current is a method which should never be resorted a tube becomes hopelessly soft, the only satisfac
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