STUDIES IS PHOTOC"ElIIC'.IL TEC'HSIQI-E. P.1RT 111 The Quartz Mercury Lain11 in Vse BY P. TI-.
C U S L I F F E . R. G . FR.\SKLIT,
R . E. 77-. I\I.\DDI>OS .%l-D L. REET-E
_____
The use of the quartz mercury lamp in this lahoratory. extending over a period of several years, has resulted in a collection of data which is non- presented primarily t o illustrate the points discussed in the previous papers of this series.] The technique of the measurement of energy tlistriliution has already lieen tlescrihetl in the second paper. and i t appears necessary only t o state that, the liurners employed were all made by the Henitt Electric C'o.. London. The working conditions and ages of the lamps are given in Taliie I, while the percentage of the total radiation emitted Iiy each line in the n-nve length range examined, namely, 2 4 S p p - 5 7 9 p p . is recortletl in Tahle 11. -Illthough the mercury spectrum contains lines of shorter wave length than 24SgpL!the spectrometric apparatus n-hich TYCS use(I did not give any cert:iin indicztion of their presence. -1consideration of the optical system s h o w that this coiild not he due to the quartz whose ahsorption in the ultra-violet is inappreciable for w t v e lengths greater than 2 2 o p p . The mirror incorporated in the spectrometer. lion-ever, possesses i i i a r l d alisorption in this region of sh art, wave length, (we graph in second pa1:er of this series p. 7 1 4 ) and to this m a y partly be att8ributedthe non-detection of the?e lines. K i t h a perfectly n e v lamp any slight indication of the lines tlisnppenretl :>fteraljcut j o hours hurning. icf. Part, I of thi I t has lieen stated in an earlier p a l m that the radiation passing a I cni. quartz-n-ater cell in the region 5 79pp-14oopp is consit1er:il)le (see figures qiiotetl in Part 11. 13. 7 2 6 . ) hut as the nieans for carrying out the necessary niensiirements were. unfortunatelp not nvailahle! the energy tli?triliution nieasiirenients are to this extent incomplete. antl cease with the yellon line at 5 7 0 i * ~ * . ('onsidering the results given jn the tables. it is ceen thst the intensity of t3heshort ultra-violet radiation. 2 8 9 p p - 2 4 8 p p . is consiclera1)ly retliicetl during the first 5 0 0 hours of the life of the ianip. [For esampie. the 1nml;s 2 d . 5. 6 antl 7 of Tahle 11.) Khile this loss is not a:: i ~ ~ p iwith t l tlie lines helow 2$3pp3 it is siifficiently great t o necessitate a retleterminntion of the energy clistrihulion every 2 0 0 hours (say) when quantitat,ive ~ o r kis cerrietl out in this region. icf. Part I! 13. 55.) The vnlna1)le property of the mercury arc as 3 r a t h t o r of short w i v e lcngths is thus attended hy this inconvenience, h i t pencling the discovery of n more permanent source it ~i-oultleplienr that i t s continiied tis? is ~ieces:ary, prol:er iiwrautions \ping okervetl. An int'eresting resuit, n-hich has since been ronfirnietl. is presented by L m i p 2 . n-hich n-as accidentnlly liroken after lieing in use for ahout 500 hours. -- -~ ._ J. Phys. ChPm.. 29. 39. 713 ( 1 9 2 . 5 : .
14.8
P. TV. C ' C S L I F F E , R . G . F H A N K L I X , R . E . \T-. 1IADDIbON A S D L. HEEVE
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S T T D I E S IX PHOTOCHEJIICAL T E C H X I Q T E
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The lain1, \vas repaired hy a 11rocess involving the heating of the whole burner in a furnace, and identical ivith that employed in the manufacture of a new lamp. The energp tli.&bution 2c vas taken immediately after the repair of the lamp. that is joo hoiirs from its first use, and again joo hours o,fter repair. or I O O G hours from its fir+t w e . The figures in 2 c contain higher values for the ultra-Yiolet antl indicate that the lamp n-zs liehaving like a new one, although actually 500 hours oltl: while thc figures in 2 d are ahout normal for n lamp 1000h o ~ r soltl. The trcatment rcceiwtl hy the lamp during the repair thus gal-e a tein1:or:uy rejiivenztion hut did not increaFe its life 1:eyond the normal. For this laiiip the percentnge decrease in the intensity of the lines has alrentl>- lieen giren. (Part I. 1). j ~1 . I t may lie Ftatetl that the usefiilness of the niercury lamp does not diminish uniformly, and the time when i t may be said t o be of no further value for photo chemical purposes arrives sutltlenly. An approsirnation to the useful life of a lamp is 1000hours. liut occasionally one nil1 1a.t longer, as is seen with Lamp which lastecl about 1400 horn?. -4s the liiirner ages, the Filica tube connecting the two electrodes become coated v i t h a h o u - n film, which has been attributed to rarious causes, e. g . , the disintegration of the electrodes. Recendy it has been stated' that the filii1 dirapl:ears and the full activityof thelnmpinay lie restored liy henting the tube in a Bunsen flame. The production of this film undouhtedly influences the intensity of the rntlia,tion eniit.tetl hy tkic lamp antl it woultl he of interest to determine the effect of the heat treatment on the energy tlistriliution ant1 on the total energy.
;*
The cha.nge in the energ>-distribution of one lamp ( S o . 3 ) . produced by an increase i n the po\ver consumed is shown in the following table.
TABLE111 13vI:itivc intensity with :ipplietl voltage of 62 yolts 65 volts IO0
Sg . 2 8.;.2
IO0
92 95.7
(There was no material change in amperage) The remainder of the lines were hardly altered either in relative or un absolute intensity, the whole effect being in agreement with that previously observed. An idee of the absdute magnitude of the energ) in n beam from the quartz mercury lanip may be gathered from the following table which refers t o Lamp 2 c , disposed as tlescribetl in Part I1 (pp. j 1 5 - j z . ~and Figs. I and 6h) and burning under the conditions given in Table I. Baker ant1 Carlton. .J. Chem. Soc., 127, 1922 (1925)
+TI-DIF:,
1431
I N P H O T O C H E I I I C A L TECHSIQCE
The figures are for the energy in the heam emerging from the water cell.
TABLE ITAipertnrebefore I n n i p I ,8
cms.
1.4
1.0
’ ”
Intensity 2 1 ,?;.
H.K.
Ii.73
:’
11.63
”
One of the ol,,iecta in preFenting the (lata, in thi? paper is to give a general itlea of the magnitude t o be es1;ectetl in the energ>- ralues of definite wave lengths in the radiation from the quavtz niercurJ- arc lamp. The individuality of the lamps cntl the importance for quentitative photochemical ~ o r kof accurately tleterinining in z?holiite units (ergs per sq. cm. per see) the intensity of a given n a v e length with the lcmp h r n i n g under lye11 defined conditions gratef idly acknowledge the helpful criticism and advice giren by Prof. *\. J. Xllmand, 3I.C.’ D.Sc. under whose direction the n-ork was carried out. One of 11s (P. TI-.C.) ccknowledges his intlehtetlness t o the BritiRh Cotton Industry Research ;lFsociation for the n\~-ardof a bursary: and the imilarly aclinon-ledge the grants iiiatle them by the Xdvisory C’ouncil of the Department of Scientific and Industrial Research. l 7 r i i i , c r s i t y of Loiido,z. K i r i g ’ s C‘ollcqe. J i t l y 2;> 1512e
