30. PHOTOCHEMISTRY OF NUCLEIC ACIDS 47 



lines. The most convenient type of source is the low-pressure quartz mer- 

 cury resonance lamp with maximum emission at 253.7 mix; included in this 

 class are also the familiar germicidal lamps with special glass envelopes. A 

 wide variety of resonance lamps 33 is available from a number of firms who 

 usually supply data regarding emission intensities at different wavelengths, 

 the fractional intensity of which, at 253.7 m/x, may be well over 90%. Ac- 

 cording to Peel, 34 the British Thermal Syndicate lamp emits 97% of the 

 total intensity at 253.7 mix, about 2.7% above 300 mix and a few tenths of 

 1 % at wavelengths below 300 mix, excluding the 253.7 line. 



Many resonance lamps emit traces of radiation at wavelengths to the 

 violet of 253.7 mix and occasionally as much as 1 % or more of the total out- 

 put at 184.9 mix. Despite the fact that this latter line is strongly absorbed 

 in air (50% absorption in 2-3 cm. air), its much greater photochemical ef- 

 fectiveness may be troublesome. Santer 35 presents data on the amount of 

 184.9 mxx radiation emitted by various resonance lamps as well as a method 

 for the measurement of the intensity of this line. By far the simplest pro- 

 cedure, however, is to filter out such radiation with a layer of 25-50 % acetic 

 acid. Surprisingly enough, even some germicidal lamps may emit traces of 

 184.9 radiation; 33 ' 36 while some lamps (cold-cathode Sterilamps) are made 

 in a number of different glasses so as to transmit desired intensities of the 

 184.9 line. 33 



For experiments where high doses are necessary, it has become common practice 

 to use batteries of as many as 6-12 germicidal lamps, the irradiated solution being in 

 shallow pans or in a series of quartz tubes. A much simpler and more convenient ar- 

 rangement, which has been in use in this laboratory for over a year, is that shown in 

 Fig. 3. The solution to be irradiated and introduced at A is contained between the 

 germicidal lamp L and the glass tube T, to the latter of which is sealed a water jacket 

 for temperature control. The diameter of the tube T is from 2-10 mm. larger than 

 that of the lamp, depending on individual requirements; it is tapered at the bottom 

 and cemented to the lamp surface at S by means of a plastic spacer and some plastic 

 cement ; it is centered at the top by several plastic spacers P. The stopcock C is sealed 

 to T through a capillary tube by means of which the solution may be stirred during 

 irradiation by passage of a stream of air or nitrogen. During the course of the reac- 

 tion samples may be drawn off via C or by means of a fine drawn-out glass capillary 

 inserted at A. Should the lamp contain troublesome radiation below 253.7 nnz, it may 

 be necessary to insert an additional (quartz) tube between T and L so as to supply a 

 layer of liquid filter; without this modification, however, we have found this source 

 suitable for preparing sizeable quantities of photo-products of pyrimidine deriva- 

 tives. 



33 L. J. Buttolph, in "Radiation Biology" (A. Hollaender, ed.), Vol. II. McGraw- 

 Hill, New York, 1955. 



34 G. N. Peel, Brit. J. Radiol. 12, 99 (1939). 



35 E. Santer, Z. angew. Phijs. 9, 105 (1957). 



36 A. Canzanelli, R. Guild, and D. Rapport, Am. J. Physiol. 167, 364 (1951). 



