8 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS to Group II (see Table I) were stable for periods up to 5 months, and the remaining four (two of Group III and two of Group IV) were stable for anything between a fortnight and four or five weeks. ULTRA-VIOLET IRRADIATION OF LIQUID PARAFFIN The ageing of liquid paraffin can be speeded up considerably by exposing it to ultra-violet irradiation. For this purpose quartz containers must be used so that the ultra-violet light has access to the liquid paraffin. It was found that although the spectra of stable liquid paraffins remained unaffected •vhen these materials were exposed in glass bottles to a mercury vapour discharge for periods of several weeks, this irradiation produced significant changes when the same "stable" materials were contained in quartz vessels (Fig. 4). 0.08 0 07 006 0O5 •00a OO3 002 o Ol ooo 2,400 2,500 2,6'00 2,700 2,800. Ultra-violet irradiation--mercury vapour lamp (125 W.) 45 cm distance. O -- Starting material No. 1. A -- Exposed in glass vessel for 643 hours. B -- Exposed in glass vessel for 1353 hours. C -- Exposed in glass vessel for 230 hours. D -- Exposed in quartz vessel for 643 hours. E -- Exposed in quartz vessel for 1353 hours. F -- Exposed in quartz vessel for 230 hours. Fig. 4. Effect of ultra-violet irradiation on two portions of a medicinal liquid paraffin. No appreciable change was obtained when the •naterial was kept in a glass vessel, whereas there was a significant increase in absorption intensity, particularly in the region of 2490 A, of the material in a quartz vessel.

SPECTROPHOTOMETRY AND MEDICINAL LIQUID PARAFFIN 9 The largest increase in absorption intensity was always found at 2490 A, even in the case of extremely pure liquid paraffins whose spectra, showed no band structure (Fig. 5). A similar type of increase of absorption intensity, though at a slower rate, was found in the neighbourhood of 2710 A (Fig. 6). / X"•-• 5 a[ler 575 hrs. in 0.09[ X ', 0,04 ••• •'x• 2,400 2 5• 256• 2 7• 2,8 Change in ultra-violet absorption on irradiation by mercury vapour lamp. Fig. 5. The largest increase in absorption intensity as the result of ultra- violet irradiation is always around 2490/• irrespective of the initial quality of the liquid paraffin.