A noteworthy process is due to Liebig. Saltpetre is melted in a crucible, and heated to a temperature below that at which oxygen is evolved. Dry chrome yellow is introduced so long as effervescence occurs; the fused mass appears, whilst liquid, deep black. As soon as it is in quiet fusion it is poured on a cold plate. In consequence of the rapid cooling it becomes brittle and can be easily powdered. The hot mass is broken up and boiled with water, potassium chromate going into solution. The chrome red made by this process is little inferior in brilliance to vermilion. According to Prinveault a handsome chrome red is obtained by treating 25 grammes of neutral lead carbonate with 10 grammes of yellow potassium chromate dissolved in 5 litres of water, boiling for half an hour, washing the violet precipitate, and finally treating with 1 gramme of sulphuric acid diluted with 100 grammes of water. =Cobalt Red= consists of cobalt phosphate. It was first recommended by Salvetat. It is obtained by precipitating a solution of a cobalt salt by sodium phosphate. After drying at the ordinary temperature the precipitate has a beautiful rose-red colour. By careful heating, the shade becomes more violet according to the temperature used. =Cobalt-Magnesia Red.=—When magnesia is moistened with the solution of a cobalt salt and strongly heated, a rose-red mass is obtained which can be used as an extremely durable artists’ colour. It probably consists of a compound of cobalt oxide with magnesia. The method of preparation is as follows: Magnesium carbonate is mixed to a thin paste with a dilute solution of cobalt nitrate; this is heated and stirred until quite dry, when the residue is strongly heated in a covered crucible. In the manufacture of this and other cobalt pigments it is of particular importance to prevent the entry of the fire gases into the crucible. Unless this is done a product of good colour is not obtained. =Cobalt Arsenate.=—By precipitating a cobalt salt with sodium arsenate, a violet-red precipitate is obtained which leaves a fine durable red on heating. The mineral erythrite has a similar composition and colour. This pigment has a bright shade, is permanent, and although it contains arsenic is not particularly poisonous, since after fusion it is little soluble. =Chromium Stannate.=—This artists’ pigment, which may be used in oil and porcelain painting, is made in the following manner (Gentele): 1 kilogramme of tin is converted by strong nitric acid into metastannic acid, 50 grammes of potassium chromate are dissolved in 1 litre of water, the solution mixed with 2 kilogrammes of chalk and 1 kilogramme of powdered quartz, and finally with the metastannic acid. The mixture is dried and strongly heated. The temperature must be raised to a white heat, at which the mass sinters and acquires a dark rose-red colour. It is then completely extracted with boiling water, when a fine powder is left.