THE evidence in favour of the view that the hydroxyl radical is present in flames has been summarised recently by Bonhoeffer and Haber (Z. Phys. Chem., 137, 263; 1928). There is no doubt that this radical is the emitter of the 3064 A. band, present in the spectra of hydrogen flames, and Hulthen and Zumstein, and Bonhoeffer have shown that this band occurs in absorption when water vapour is heated to high temperatures. The discovery of the existence of this radical in flames has an important bearing on the development of our knowledge of mechanisms of the reactions occurring in hydrogen and hydrocarbon flames.