surface over an area 100 feet wide and 350 feet long. T h e instrument will also detect variation in potassium content in rocks; hence it may .be able to tract contacts between acid and basic rocks under overburden.
CHEMICAL W O R L D THIS WEEK*
RESEARCH P R O G R E S S Looking for uranium? A gamma ray detector has been built to w o r k on the same principle as that of ultraviolet light causing mineral fluorescence
allegedly far superior to the conventional Geiger counter, has been described recently by George M. Brownell, professor of geology, University of Manitoba. Called the "scintillometer," it has several advantages over the Geiger counter, according to Prof. Brownell, distinguishing for one thing between uranium and thorium radiation. Tests have already been made in three important mineralized fields in Canada and results to date seem to give good promise for this instrument. The scintillometer incorporates the latest development in photoinultiplier tubes which multiply the effect of crystal scintillations by nearly a million times. This makes it capable of detecting even to an accuracy of 100% the gamma rays that enter the crystal and of measuring their effect quantitatively to a high degree of accuracy. In the case of the Geiger tube 99 to 99.9% of all the gamma rays that strike such tubes pass through without causing any effect. In contrast, the scintillometer, employing a dense crystal, records scintil-
lations from nearly every gamma ray that penetrates it. In one recent test three single-tube Geiger counters gave, respectively, 28, 70, and 105 counts per >
