APPLICATIONS AND SOURCES OF ULTRAVIOLKT 55 



closely woven textile gloves, but these gloves should be tested before long- 

 time use. 



The discomfort from ultraviolet-irritated eyes may be relieved by 

 exposing them for 15-20 min to as high an intensity of heat as can com- 

 fortably be borne from a heat lamp or from an ordinary 50- to 60- watt 

 incandescent lamp held close to the eyes; the treatment is effective 

 through closed eyelids (author's personal experience). In extreme cases, 

 a doctor should be consulted, but when this is impracticable, the usual 

 first-aid treatment is the application of ice packs. In any case, the irri- 

 tation produced by the ultraviolet may disappear within a day or two and 

 much more quickly than a corresponding degree of irritation from a longer 

 wave ultraviolet source. A severe conjunctivitis may, however, make 

 the eyes susceptible to secondary infection until the lesions are healed. 



COMMERCIAL SOURCES OF ULTRAVIOLET 



Mercury-vapor sources of ultraviolet for practical and experimental 

 uses may be grouped as (1) commercially available low-pressure (0.004- 

 0.02 mm of Hg) germicidal lamps, (2) high-pressure (400-60,000 mm of 

 Hg or 0.5-75 atm) photochemical, therapeutic, and filtered sunlamps, and 

 (3) special experimental lamps of limited availability. The character- 

 istics of all but the low-pressure lamps are discussed later in this chapter. 



Arc lamps with rare-earth cored carbons provide powerful sources of 

 energy for many photochemical, photographic, and photocopying appli- 

 cations of the ultraviolet. For various reasons their biological applica- 

 tions have been rather limited and are not discussed in this chapter. 



HIGH- AND LOW-PRESSURE MERCURY ARCS 



As indicated graphically in Fig. 2-5, low-pressure mercury arcs are 5- 

 10 times more efficient in germicidal action than high-pressure arcs in 

 envelopes of the same transmission. It should be noted that high-pres- 

 sure quartz-mercury arcs may be of practical use, regardless of efficiency, 

 in places where it is impossible to provide the essential ultraviolet inten- 

 .sities from the much more bulky low-pressure lamps. For example, the 

 germicidal effect per unit of total volume of a 360-watt high-pressure arc 

 in quartz is 5-10 times that from low-pressure arcs, but the germicidal 

 efficiency of the high-pressure arc is one-fifth to one-tenth that of the low. 

 For another example, the germicidal effectiveness of the radiating part of 

 the UA-3 and UA-11 high-pressure mercury arcs of Table 2-6 can be 

 duplicated only by 8-12 times the radiating length of the more efficient 

 low-pressure lamps. 



ULTRAVIOLET OF WAVE LENGTH 2537 A 

 INHERENTLY LOW EMISSION INTENSITY OF SOURCES OF 2537 A 



The possibility of a source of 2537 A ultraviolet with the high power 

 output per unit of source area, or radiant-flux density, of the high-pressure 



