KOLTHOFF (J. Amer. Chem. Soc., 1926, 48, 1447) states that he has been unable to confirm our statement (Jour. Chem. Soc., 1925, 127, 150) that fused borax loses sodium oxide. He reports that “even after the substance had been heated for two hours at 800° the weight did not change”. His experiments, however, appear to be scarcely precise enough to prove that borax on heating (1) is not volatile, and (2) does not change in composition; as a matter of fact the volatility of borax at high temperatures is well established, having been observed by Hoskyns-Abrahall (Jour. Chem. Soc., 1892, 61, 650), Leonard (Chem. News, 1898, 77, 104), and Smith and Van Haagen (“The Atomic Weights of Boron and Fluorine”, Carnegie Inst. Washington, Publication No. 267, 1918).