X-Rays, Apparatus and Methods Page 18

paratively trivial differences in procedure make all the difference between success and failure. We describe here the method which we follow and which allows us to count with certainty upon securing at least nine successful plates for every ten exposures.

General Adjustment. — First see that the coil is working smoothly and so as to give a uniform discharge in the primary. The secondary spark points should be separated by the distance given by the makers as proper for the tube. The coil must then be adjusted either by changing the E.M.F. at the primary or by variation of the vibrator adjusting springs, so as just not to spark over this air gap. The tube should then be joined in parallel with this secondary spark gap. The coil may then be started up, using the fluoroscope to show whether direction of discharge is right. If not, the primary current should be reversed. If X-rays are not now profuse, the secondary discharge points should be further separated and the vibrator springs tightened so as to produce correspondingly greater discharge. Continue this until either X-rays are secured as desired, or the tube becomes too hot, or possibly bluish or pink in color. Blue denotes too low a vacuum to expect X-rays, but often a gentle running of the tube for ten or fifteen minutes, while in this condition, will raise the vacuum to a suitable value. Pink denotes a very low vacuum and usually means, in a tube which has ever been right, a puncture or leak; such a tube can only be made good by re-exhaustion and repair. With many tubes a vivid green fluorescence is the sign of the X-ray vacuum. With the Bowdoin tubes, as also with many others, the most efficient condition is with the platinum reflector plate at cherry-red heat over an area of one-half or two-thirds that of the little finger nail.

Sometimes the vacuum will be too high for the production of X-rays with any length of secondary discharge. It may be reduced by gentle warming of the tube by a spirit-lamp flame. Sometimes reversal of the current in the tube will answer, but this is apt to blacken.

Sticking of the Vibrator must be guarded against — it is often fatal to the tube. This is because of the much larger