Silica 51·21 Iron protoxide 20·72 Magnesia 6·16 Water 4·49 Alumina 7·25 Soda 6·21 Manganese protoxide trace. While a Cyprus earth showed:-- Per cent. Silica 51·5 Iron protoxide 20·5 Magnesia 1·5 Water 8·0 Potash 18·0 The presence of copper would point suspiciously to adulteration, and in any case should suffice to condemn the sample for use. Naturally there is considerable variety of tint among the many kinds of terre verte, but they all belong to the pale greyish class, and are more or less translucent, consequently their covering power is small. Their value lies in their durability, and the resistance they offer to the injurious effects of strong light and impure atmosphere. They can be employed either as oil or water colours. The only preparation to which the natural pigments are submitted is fine grinding and washing. TITANIUM GREEN.--An excellent dark green pigment, though rather costly, can be prepared from rutile or any titaniferous iron ore by the following method:-- The ore is dressed clean, and fused with twelve times its weight of acid sulphate of potash in a crucible. When cool, it is reduced to fine powder, and digested at 120° F. in dilute hydrochloric acid (half water) until solution is complete. The hot solution is filtered off from the residue and carefully evaporated down to a syrupy consistence, when the nearly pure titanic acid is allowed to cool in the dish and thrown on a filter. When sufficiently drained, it is boiled in a large volume of water containing a little ammonia, and the precipitated titanic acid is filtered and washed. If an ore is used containing carbonate of lime, it must first be treated with dilute hydrochloric acid before the sulphate of potash is applied. The titanic acid on the filter is next mixed with a concentrated solution of sal ammoniac, and again filtered. Then it is digested in dilute hydrochloric acid at 120° to 140° F. till the solution is complete. On adding ferrocyanide of potassium to the acid liquor, and bringing quickly to a boil, a precipitate of ferro-cyanide of titanium is thrown down. This is very carefully and slowly dried, at a temperature never exceeding 200° F. VERDIGRIS.--The chemical examination of verdigris shows it to be a basic hydrated acetate of copper, containing variable proportions of the bibasic and tribasic acetates.