The mixture of salts was heated to remove water of crystallization, the purpose of the ammonium iodide being to prevent hydrolysis of the calcium iodide. The dehydration was carried out either by heating in vacuo, first at 200 then at a higher temperature until anhydrous and molten;or by heating small batches of the mixture in an evaporating dish in the strong draft of a fume cupboard to remove ammonium iodide and water. Anhydrous salt mixtures of melting points between 350 and 375 were thus obtained.nThe calcium iodide/potassium iodide solids were stored in a desiccators above silica gel until required. As they were extremely hygroscopic it was found difficult in practice, to exclude a small amount of water pickup during subsequent transfer to the reaction vessel. The salt system was selected because its melt is a good solvent for calcium metal and its melting point is reasonably low.
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