The following thermal data have been measured f or some of t he compounds and metals of cerium and neodymiumz (1) the heats of solution and dilution of the anhydr ous chlorides i n aqueous solution; (2) the changes in heat capacities of solution and dilution of the anhydrous chlorides in aqueous solution; (3) the heats of solution of the anhydrous chlorides and metals in aqueous hydrochloric acid; (4) the heats of solution of the hydrated chlorides in aqueous solution; ( 5) the heats of precipitation of the oxalates in aqueous oxalic acid solution; and (6) the heat capacity of neodymium metal in the temperature range of 0° to 250°C. In addition, the heats of solution and dilution of potassium chloride and oxalic acid hydrate in aqueous solution, and the heat capacity of tantalum metal from 0°C to 425°C have been measured.