BROWN MINERAL PIGMENTS. =Lead Brown.=—When red lead is treated with nitric acid, lead monoxide is dissolved, whilst deep brown lead peroxide remains. When the action of the nitric acid is finished the residue is well washed and dried. Lead peroxide is now extensively used for lucifer matches; it readily gives up oxygen on heating, and thus accelerates the ignition of the composition. Brown match-heads owe their colour to lead peroxide. =Manganese Brown= consists of manganic oxide; it occurs in nature, but seldom in a state of sufficient purity to be used as a pigment; it is, therefore, generally made artificially. The process is very simple. A solution of manganese sulphate is precipitated by caustic soda solution, the manganous hydroxide produced is quickly changed by the action of the air into manganic hydroxide. The colour is most rapidly developed when the precipitate is spread out in thin layers; it is well washed after it has changed to brown. =Pyrolusite Brown= is manganese peroxide in a state of fine division. It can be made from the residual liquors of the preparation of chlorine by adding sodium hypochlorite. A brown precipitate results, which is kept in contact with the liquid until it no longer changes in colour. It is then washed with water slightly acidified with sulphuric acid, and finally with pure water. When finely powdered, manganese peroxide has a very fine brown colour. It is quite unaltered by the air and thus, in consideration of its cheapness, deserves a much greater use than it has yet found. =Prussian Brown.=—When Prussian blue is heated in air it soon begins to glow, and is converted into a brown mass, the shade of which depends on the amount of impurity in the Prussian blue. It is desirable to use Prussian blue quite free from impurities, so that a brown of the same shade is always obtained. The brown obtained can be shaded by additions of indifferent substances. =Iron Brown.=—By igniting a mixture of 100 parts of finely levigated natural yellow ochre with 5 parts of common salt a brown product is obtained, which is pale or deep according to the temperature used. It is a cheap and durable colour. =Copper Brown.=—According to Cartheuser solutions of 2 parts of copper sulphate and 1 part of Epsom salts are mixed, and a strong solution of potassium carbonate gradually added so long as a precipitate forms. The precipitate is washed, dried and ignited, when copper brown is obtained as a brown powder of great permanence in air. According to Schreger solutions of 2 parts of copper sulphate, 2 parts of alum and 0·5 to 1 part of ferrous sulphate are mixed, potassium carbonate solution added, the precipitate dried and ignited. The redness of the shade is proportional to the quantity of ferrous sulphate.