Methods of Altering

1  Nature of Tubes.

I. Softening may be necessary to utilize an old tube, or to adapt any tube for a special purpose requiring a lower degree of penetration. This may be effected in various ways :

(a Use of regulators, as described above, is the preferable method.)

In the absence of a regulator—

(6) Baking the tube for Borne hours in an oven at a high temperature may somewhat soften a tube per- manently.

(c) Laying the tube aside for a year or more induces some degree of softening.

(d) Heating the tube carefully, by the flame of a spirit-lamp or before a fire, softens it temporarily, but on cooling the previous hardness is reassumed.

A tube may be thus softened while in the live circuit (that is, with current passing, or tending to pass, through it). Thus natural softening may be hastened, or the vacuum initially reduced, to allow discharge through the tube to commence. In such a case the spirit-lamp employed should be held on a long insu- lating handle, so as to protect the operator from shock or X-ray burn. Care must be taken in so heating a tube that no part is over-heated, as a dent may be readily produced in the softened glass by the atmospheric pressure outside acting against the much-reduced pressure within.

All softening processes should be carefully regulated, and must not be carried too far, since hardening is difficult, and always more or less injurious to the tube.

II. Hardening should never be called for where a graded stock of tubes is kept as advised, and where due care is exercised in use of the tubes or in any softening process called for. Where under special conditions hardening may be necessary, it is best done by—

(a) Sending the current through the tube in the inverse direction for a short time, the effect being similar to that described as causing the gradual harden- ing of tubes through continual use.

(b) Villard’s method, by heating an open tube or sleeve placed over an osmo-regulator, whereby the ordinary softening function of that arrangement is said to be reversed and hydrogen drawn out of the tube, is un- satisfactory in practical use. This method is illustrated in Fig. 9.

(c) The automatic side-tube regulator, represented in Fig. 7, is also said to be available for the purpose of hardening. To do so, it is advised to remove the positive wire from the anode of the X-ray tube, and to connect it to the terminal at that end of the side-tube, the negative wire being connected to the kathode ter- minal as in ordinary excitation of the X-ray tube. The side-wire of the regulator must be well separated from the kathode terminal, and current then passed through. We have not used this method frequently, nor do we recommend it.

On the rare occasions on which hardening has been called for, we have found the first-mentioned method the most serviceable.

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