The photochemical production of gold sols using artificial light.

Twenty years ago (Fowweather, 1928) a method for the preparation of gold sols for the Lange test on cerebrospinal fluids was published in which gold potassium bromide is reduced by potassium oxalate under the action of daylight. Temperature and light intensity were found to be complementary to some extent; thus it was found advisable to carry out the reaction at a somewhat raised temperature in winter, when daylight intensity is comparatively low. Hoess (1931) advocated the use of a " vitalux" lamp, and Herrmann (1935) measured the light intensity by a light meter and adjusted the temperature to the intensity of light. The modifications were not entirely satisfactory, and the search for a satisfactory light source which should be reasonably constant during the course of a preparation continued; two methods were successfully developed during 1940, and one or other has been in use here ever since. The first uses an ultra-violet lamp and the second a high-power electric lamp of conventional pattern.