In the study of the physical properties of non-aqueous solvates considerable work has been done on the systems magnesium bromide-diethyl ether (1-3) and zinc bromide-diethyl ether (4). It is planned to extend these studies to the bromides of other elements in the same periodic group as well as to related compounds. One of the authors (R) during a study of the three component system, water-diethyl ether-magnesium bromide, tried to determine the amount of water in a sample of ether solution by use of the drying agent Dehydrite, which is anhydrous magnesium perchlorate. It was noted that the magnesium perchlorate appeared to retain considerable ether even when heated. Since other magnesium compounds form etherates, especially the halides, it was decided to investigate this phenomenon further by means of solubility measurements of anhydrous magnesium perchlorate in diethyl ether. Willard and Smith (5) had previously determined the solubility of this compound in numerous solvents including diethyl ether at 25°. The present work was done at 0°, 15° and 25°
