400 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 2 



about 10 minutes after the arc has been started. For local treatment 

 a -water-cooled quartz mercury vapor arc light is frequently em- 

 ployed either with or without quartz compression lens or other quartz 

 applicators, varying with indications. 



Carhon arc. — The spectral components emitted by the carbon arc 

 are similar to sunlight, except for an additional band at 3,883 

 Angstrom units, but vary in intensity. The total radiation emission 

 and the relative intensity of some of its spectral components may be 

 altered by varying the voltage and amperage, by altering the 

 diameter of the carbons, and by impregnating the carbons with suit- 

 able metals or salts.^^ The plain carbon arc of low amperage (from 

 3 to 10 amperes) has rarely proved of clinical value in local applica- 

 tions; those of higher amperage (20 or more amperes), especially 

 those burning impregnated carbons, have been reported effective in 

 general body exposures. The high intensity arc has an output of 

 total energy closest to sunlight. Nickel, iron, titanium, aluminum, 

 and tungsten are all employed for impregnating the carbons.**^ 

 Groups of (from 20 to 30 amperes) carbon arc lamps are often used 

 for irradiation of several bedridden or ambulant patients; high am- 

 perage lamps (from 50 to 125 amperes) are, as a rule, used chiefly for 

 groups of patients. There are those utilizing 90 amperes that can 

 irradiate 12 or more patients at a time. The cost of installation, the 

 operation charges of large carbon arcs and the care necessary make 

 them useful chiefly for the handling of groups of subjects in 

 institutions. 



Of the ultra-violet rays, the plain carbon arc emits chiefly the 

 longer (near 400 millimicrons) ; that below 300 millimicrons is com- 

 paratively weak. Carbons with special impregnations or cores now 

 employed in carbon arc lamps emit additional radiation characteristic 

 of the metal or chemical emplo3^ed within the carbon. Carbons im- 

 pregnated with iron, tungsten, titanium, and nickel emit rich ultra- 

 violet zones down to about 220 millimicrons; in addition, carbon-arc 

 sources emit much infra-red and red radiation. With great energy 

 input, carbon arcs can emit a large quantity of radiation. For best 

 efficiency, a definite relationship must exist between the diameter of 

 the carbons and the amperage employed. 



The greater the amperage, the more heat is generated. A lower 

 amperage arc can be operated nearer to the patient because its 



^ Coblentz, W. W., read before Illuminating Engineers Society, Chicago, Oct. 14, 1927. 

 Luckiesh, Matthew, Ultra-Violet Radiation, New York, D. Van Nostrand Co., 1922. Grif- 

 fith, H. D., and Taylor, J. S., Journ. Hyg., vol. 25, p. 218, July, 1926; Radiology, vol. 

 10, p. 93, February, 1928. 



^Luckiesh (footnote 45). Coblentz, W. W., Sources of Radiation and Their Physical 

 Characteristics, Journ. Amer. Med. Assoc, vol. 95, p. 411, Aug. 9, 1930. Coblentz, W. 

 W., Dorcas, M. J., and Hughes, C. W., Radiometric Measurements on the Carbon Arc 

 and other Sources Used in Physical Therapy, idem, vol. 88, p. 390, Feb. 5, 1929. 



