. A text-book of radiology . soon befound that the vacuum is getting too low. It can besaved if the current is reduced at once, or cut offentirely so as to let the tube cool. If this is not done intime considerable shortening of the useful life of thetube will take place. On the other hand, if at first it is only used forradiography of the thinner parts as hands and toes, or ifin treatment, care is taken to pass but a very smallcurrent, the tube will not only be found to remainsteady or even rise in vacuum, but concurrently itgradually develops an increasing degree of stability. 52 TEXT-BOOK O
. A text-book of radiology . soon befound that the vacuum is getting too low. It can besaved if the current is reduced at once, or cut offentirely so as to let the tube cool. If this is not done intime considerable shortening of the useful life of thetube will take place. On the other hand, if at first it is only used forradiography of the thinner parts as hands and toes, or ifin treatment, care is taken to pass but a very smallcurrent, the tube will not only be found to remainsteady or even rise in vacuum, but concurrently itgradually develops an increasing degree of stability. 52 TEXT-BOOK OF RADIOLOGY. A stage may eventually arise when it will not onlyeasily stand double or treble the amount of current, butwill do so for more or less prolonged periods of time. A tube in this condition is said to have become seasoned. This seasoning of a tube is an art, but awell-seasoned tube is a joy to possess and repays anytrouble it has taken to get it into this condition. Figures 17 and 19 are varieties of the heavy anode. Fig. 20. Tungsten-faced Anti-Cathode. type of X-ray tube. In the first one the block of metalis mounted on the end of a strong iron tube which is agood fit in the glass stem of the bulb. These heavyanode tubes are very popular among X-ray 16 has a water-cooled anti-cathode, but calls forno further description. Lately, the metal tungsten has been introduced forfacing the anti-cathodes of X-ray tubes, and such tubes,either air or water-cooled, are now obtainable. In addition to the very high melting point of tungsten,which makes fusion practically impossible in an X-ray CHOICE OF X-RAY TUBES. 53 tube under usual conditious of working*, we have seenthat a target of this metal makes a more efficient producerof X-ray energy than metals of lower atomic these reasons tungsten is becoming very generallyused, and with the great improvements in exhaustion ofthe bulbs the present-day tungsten-faced, heavy anodeX-ray tube is a vast improvemen
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