WHITE ANTIMONY PIGMENTS. Antimony forms a number of white compounds which can be made by a simple and inexpensive process, and might, therefore, be used as pigments. Two antimony compounds in particular are so used—antimony trioxide and oxychloride (powder of algaroth). =Antimony Trioxide= occurs ready formed in nature as white antimony or antimony bloom. It is very simply prepared by burning the metal in air, when it forms soft needles with a silvery lustre. It is only necessary to heat melted antimony to a little above its melting point in a crucible placed in a slanting position, when the metal takes fire and burns with a blue flame. Nitric acid converts metallic antimony very quickly into antimony oxide with a copious evolution of brown fumes. Antimony trioxide may be more cheaply prepared from antimony sulphide, artificial or natural (stibnite), by finely powdering, moistening with water, and gently warming on plates. Oxidation takes place, the sulphur is converted into sulphur dioxide and the antimony to trioxide. The heating should not be carried too far, or the antimony takes up further oxygen and forms the tetroxide. =Antimony Oxychloride, or Powder of Algaroth=, is obtained by dissolving stibnite in strong hydrochloric acid, the operation being performed under a chimney to carry off the sulphuretted hydrogen. The solution of antimony trichloride, when the impurities have settled, is poured into a large vessel of water. At once a pure white precipitate is formed, which quickly sinks; it is washed with water until the washings have no acid reaction. Washing should not be continued too long or the oxychloride will be further decomposed; by washing with hot water it is almost entirely changed to antimony trioxide. The precipitate, after washing with cold water, has generally the composition expressed by the formula SbOCl. Antimony oxide and oxychloride are both very crystalline powders, and have in consequence small covering power. =Bismuth White= is not used as a painters’ pigment; it has no advantage over the white pigments previously described, and is much more expensive. Its only use as a pigment is for the preparation of white cosmetics, and even for this purpose zinc white is now frequently used; it is cheaper and quite as satisfactory. Bismuth white is prepared by treating metallic bismuth with fuming nitric acid. The white precipitate at first formed completely dissolves in an excess of acid, and when the solution is poured into a large quantity of water, basic bismuth nitrate—bismuth white—separates. Pure bismuth white is a soft, heavy powder, brilliantly white; it must be preserved in air-tight vessels as soon as it is dry, otherwise it acquires a yellowish tinge. Bismuth compounds are, if possible, more susceptible to the action of sulphuretted hydrogen than lead compounds. The yellow colouration, turning to black in the course of time, is due to black bismuth sulphide.