FURTHER details are given in the latest Berichte, by Prof. Victor Meyer and Dr. Hartmann, concerning their recently discovered basic compounds of iodine. It will be remembered that the fundamental base from which these new substituted bases are derived is the hypothetical compound HO.IH2, and that the derivative had been isolated as a strongly alkaline substance readily soluble in water, and which forms salts with acids with elimination of water, exactly like ammonium hydroxide. For the parent substance, therefore, the name iodonium hydroxide is proposed. At the conclusion of their first paper, Prof. Meyer and Dr. Hartmann announced that they had just succeeded in isolating the simpler di-phenyl derivative OH.I (C6H5)2, and the present communication describes the strange mode of its genesis, and the character of the free base and its salts. The beautifully crystalline iodide was frequently obtained in small quantities during the whole course of Prof. Meyer's work with iodoso-benzene. It was observed that methyl iodide acts with great energy at the ordinary temperature upon the latter compound, and the product yields in contact with moist silver oxide a liquid from which potassium iodide precipitates crystals of the new iodide, I.I (C6H5)2. It was subsequently found that when iodoso-benzene itself is triturated with moist silver oxide, the filtered liquid likewise yields similar crystals of diphenyl-iodonium iodide upon the addition of potassium iodide. This discovery led to a systematic study of the conditions of the reaction, and it was eventually elicited that freshly prepared iodoso-benzene is incapable of so acting, bat that by a few days' exposure in a thin layer to daylight, or, better still, by heating for some hours to 60°, it is rendered capable of producing the new base when brought in contact with oxide of silver. Moreover, it was ascertained that potash or soda are likewise capable of bringing about the change, although owing to subsidiary decompositions, not so advantageously as moist oxide of silver. It has finally been proved that the reaction depends upon the fact that upon heating to 60° or exposure to sunlight iodoso-benzene, C6H5.IO2, is partially converted into the more highly oxidised compound C6H5.IO2, and by the action of moist silver oxide upon the mixture of the two diphenyl-iodonium hydroxide and silver iodate are produced, in accordance with the following equation:— C6H5.IO + C6H5.IO2 + AgOH = AgIO3 + HO.I(C6H5)2.