Evening twilight airglow emissions of OH (7,2) band and Li 6708 A are observed by DunwManring type photometer and following important results are obtained.(i) Intensity of OH (7,2) and Li (6708 A) decrease exponentially during evening twilight period. (ii) OH (7,2) band covaries with Li (6708 A) during evening twilight period. (iii) Empirical equations of OH (7,2) band with time is obtained. (iv) Possible explanations of such type of variations is also presented.

The light scattering properties of Acacia Catechuic Acid (ACA) was studied -in aqueous mixture of ethanol containing 0.02 mole/l. KC1. There was hardly any effect upto 25% alcohol, above which the molecular weight appeared to increase gradually till 50% alcohol in the mixture and at 55% there was precipitation of the acid.The root mean square end-to-end distance remained almost unaffected at lower concentration and reached a minimum value at about 25 yo (3052 A) beyond which there was considerable increase reaching up t o a maximum limit of 3597 A at 50% (as against 3270 A in water). This interesting behaviour of ACA in the above mentioned system could be explained in the light of the FLORY-FOX equation in conjunction with association of molecules by their hydrophobic groups which was favoured by addition of alcohol. Alcohol, however, at low concentrations did not appear to affect the character of the solvent to a great degree but beyond about 25%, the solvent behaved as a poor one. ZUSAMMENFASSUNG: Die Lichtstreuung von Akazien-Catechu-Saure (ACA) in waDrig-athanolischen Losungen (mit 0,02 mol/Z. KCl) wurde untersucht. Bis zu 25 yo Athanolkonzentration in der Losung war praktisch keine Wirkung zu erkennen. Bei hoheren Alkoholkonzentr ationen (bis 50 yo) beobachtet man eine stetige Zunahme des Molekulargewichts, und bei 55 V O~. -~~ fallt die Saure aus. Die Wurzel aus dem Quadrat des mittleren Fadenendenabstandes war bei niedrigen Alkbholkonzentrationen konstant (3270 A), fie1 dann bis zn einem Minimum bei 25% Alkohol ab (3052 A), nm dann wieder bis zu einem Grenzwert von 3597 A bei 50% hithanol zu steigen.Dieses interessante Verhalten der ACA laDt sich an Hand der Gleichung von FLORY und FOX erklaren, wenn man aul3erdem beriicksichtigt, daD die ACA-Molekule uber ihre hydrophoben Gruppen assoziieren konnen, was durch die Zugabe des Alkohols begiinstigt wird ; Losungen mit mehr als 25 yo Alkohol sind schlechte Losungsmittel fur ACA.

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