180 TABLE 66. Pouarization In Heavy MIneRaL OIL ar —4 + 1°C Band edge, mu Compound 3. p-Bis(2-(5-phenyloxazolyl)]benzene (“POPOP’’) 6. 4,4’-Di(undecyloxy“-1)-1,1’-binaph- 395 360 thyl 7, 9,12-Di(n-oetadecyloxy }benz[e]- 440 acephenanthrylene Upperline: A,myu Lowerline: polarization (P), % 375 +43 350 360 +43 240 340 +43 330 320 +42 320 32k +26 310 300 +11 300 +41 +38 +25 +33 +33 +82 410 395 375 355 340 320 800 +32 +32 +28 +24 +13 +11 +17 300 +31 290 +20» 310 —15 300 —19 390 370 +45 340 +45 300 +43 9. Tetraphenyl ethylene 380 350 +41 330 +38 310 +35 430 11. Trans-1-(4-biphenylyl) -2-(1- 390 12. Trans-1-(4-biphenyly})-2-pheny]- 365 13. 1,3,6,8-Tetraphenylpyrene 425 naphthyl) -ethylene ethylene +32¢) +41 8. Dipheny!stilbene 10. 1,8-Diphenyl-1,3,5,7-octatetraene 290 +5 290 400 +41 380 +44 350 378 +40 365 +45 335 360 +40 350 +44 325 345 +41 335 +44 305 330 +38 320 +43 290 300 +26 305 +40 290 +42 +43 +43 +42 +439 400 +42 380 +41 370 +40 350 +35 330 +28 320 +18 ()} or butyloxy or octyloxy. 6) at 290 mu, absorption bythe solvent is appreciable (A = 0.3). Whetherthis affects the result is conjectural. Theory shows that if no depolarization takes place flow directly into the chamber, now flowsfirst through sion is (a) +50% when absorbing and emitting os- the chamber into temperature equilibrium with the gas in the chamber. Rapid temperature fluctua- between absorption and emission, and if there is no mixing of types, the degree of polarization P of emis- cillators are parallel, and (b) —3344% when per- pendicular to each other. If there is overlap, the result will be somewhere between the two extremes. De- polarization (the result of rotation during the lifetime of the excited state), of course, reduces the (absolute) value of the polarization, but its effect is easily distinguished from that being discussed. De- polarization affects the whole absorption spectrum, whereas the effect being discussed is a function of wavelength. A principal difficulty encountered originally, es- pecially as it affected the viscosity-effect study, was temperature instability. Through modifications of the apparatus, improved, though not completely satisfactory, temperature control has been obtained. A hollow jacket, thermally insulated on the outside, was added surrounding the cell chamber. The jacket, filled with an antifreeze solution, has in it also copper tubing coiled around the chamber. The cold nitrogen gas, which originally was allowed to the copper tubing in the jacket before entering the chamber, thus tending to bring the surroundings of tions in the chamber have been eliminated, but the aim of holding the temperature invariant has not been realized. It was thought that creation of slush in the jacket would assure constancy; however, it was found that even then there is a temperature gradient in the jacket. The possibility of using more effective insulation is being investigated. A distinct improvement has been made in connec- tion with the solvent used. A heavier mineral oil has been obtained (Fisher Paraffin Oil 0-120), of Saybolt 335/350, and an unexpected bonus has been its transparency. Because of the improvement in the latter, the range in which meaningful results can be obtained has been extended downwards to about 290 mp. The absorbance of this oil in the 1-cm cell does not reach 1.0 until 285 mp. The increased viscosity has lessened the depolarization so that higher values of polarization are now realized. The limita-