=Nickel Yellow= consists of nickel phosphate. It is obtained by adding sodium phosphate to a solution of nickel sulphate or nitrate, and heating the pale green precipitate to redness. Nickel yellow has a pleasing shade, and is distinguished by great permanence. Up to the present it has found little use as an artists’ colour, but on account of its permanence, which does not distinguish many yellow pigments, its use is to be recommended. =Mercury Yellow or Turpeth Mineral= is a basic mercuric sulphate of the formula Hg₃SO₆. It is obtained by heating 10 parts of mercury with 15 parts of sulphuric acid in a porcelain dish in a good draught, until a white crystalline mass of neutral mercury sulphate remains. This salt, HgSO₄, is decomposed in contact with water into free sulphuric acid and a basic salt of the above composition. The decomposition is effected by treating the finely powdered neutral sulphate with hot water so long as the washings are acid, when a handsome lemon yellow substance remains. The wash waters contain acid mercuric sulphate. They are allowed to stand with mercuric oxide so long as this is dissolved, and the solution then used to prepare new quantities of mercury yellow. Turpeth mineral has a very bright shade and great covering power, but it has little permanence. Sunlight soon turns it grey, and air containing sulphuretted hydrogen in a short time turns it quite black, mercury sulphide being formed. =Yellow Arsenic Pigments.=—The extremely poisonous character of arsenic pigments has practically banished these handsome and cheap colours from use. In many countries their use is justly illegal. The majority of arsenic pigments have, therefore, merely historic interest. The two yellow arsenic pigments are found in nature as realgar and orpiment; though these are not rare minerals, the artificial products were generally used as pigments, and when they were in common use they were generally made in metallurgical works, in which minerals containing arsenic were treated. Realgar, As₂S₂, has an orange red colour, whilst orpiment, As₂S₃, is a pure yellow. When these substances were used as pigments they had the same drawbacks in regard to mixing with other pigments as other sulphur compounds. King’s yellow is finely powdered natural or artificial orpiment. =Lead Arsenite= is a permanent deep yellow, but extremely poisonous. It can be made by fusing an intimate mixture of 100 parts of white arsenic with 75 parts of gold litharge, grinding and levigating the mass. Cadmium yellow, which has still more permanence and is less poisonous, replaces this pigment.