Kleinite, as announced in 1905, belongs to the so-called mercury ammonium compounds, but no probable formula can be deduced from the analyses. It may be a mixture of a mercury-ammonium chloride in great preponderance, NHg2Cl.1/3H2O, with an oxychloride and sulphate or oxysulphate of mercury. Terlinguaite is a mercuric-mercurous oxychloride, HgO.HgCl, the formula of Moses being confirmed and the mixed nature ascertained by tests. Eglestonite is a mercurous oxychloride, Hg2O.2HgCl, the first authentic instance of such a compound, either artificial or native, and not Hg6Cl3O2, as believed by Moses. Montroydite is mercuric oxide, as supposed by Moses, and proven now by direct determination of its oxygen content.