. Radiography and radio-therapeutics . k being done. If regulation is necessary,proceed to adjust the regulatingrod at a distance which will allow sparks to pass between the rod andthe cathode until the tube works smoothly, and then remove the regulatingrod away from 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 superficial X-raytreatment until it attains the necessary degree of hardness. Hardeningby means of reversing the current is a method which should never beresorted to
. Radiography and radio-therapeutics . k being done. If regulation is necessary,proceed to adjust the regulatingrod at a distance which will allow sparks to pass between the rod andthe cathode until the tube works smoothly, and then remove the regulatingrod away from 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 superficial X-raytreatment until it attains the necessary degree of hardness. Hardeningby means of reversing the current is a method which should never beresorted to. When a tube becomes hopelessly soft, the only satisfactorything to do is to have it re-exhausted. When work is finished, if the tube is not kept permanently in position,it should be removed from its shield with great care, particularly whilewarm. If possible, it should then be placed upon a padded rack. Description of Methods used for Reg-eneration of the Vacuumof the X-Ray Tube.—All tubes (excepting those of very simple construc-. FiG. 58. -Connectiou of the X-ray tubes to tube on positive pole. 76 RADIOGRAPHY tion) are fitted with a device for lowering at will the vacuum or internalresistance of the tube. The provision of this regulator materially increasesthe Hfe of the tube. It should, however, be always borne in mind thatregulation is to be regarded as the ultimate process, and not as incidentalto the working of the tube. The number and variety of the regulators of X-ray tubes is a strikingdemonstration of the fact that the perfect regulator has yet to be of the present-day regulators are efficient up to a certain point. A fewof the most commonly used will be described. The Mica Regulator.—This consists of a small auxiliary chamber, inwhich is placed an electrode supporting a series of discs of mica. Facingthe discs is a small metal knob which has no utihty other than that of pre-venting a possible puncture of the tube, while regulation is
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