Abstract
Approximate data are given on the vapour pressures, in the range 10−1 to 10−3 mm. of mercury, of many of the cerium group of rare‐earth halides. The vapour pressures were determined by the method of molecular effusion. Also, a method is described for dehydrating these halides such that in their anhydrous form they are free from any basic salts and are 100% volatile in vacuo.