(3) Make one solution of 10 lb. of yellow prussiate, and another of 8 lb. of green copperas, water being the solvent in both cases. Mix these two solutions together and give them an hour’s boiling. Add 3 lb. of a mixture of nitro-sulphuric acid, containing 2 parts of the former to 1 of the latter. Boil for another hour. Let the solid pigment precipitate itself thoroughly, and then filter, wash, and dry as in the other cases. (4) Dissolve about 1 cwt. of perchloride of iron and 10 lb. of sulphate of soda in water. Also dissolve in another vessel 2 cwt. of yellow prussiate and 10 lb. of sulphate of soda. Pour the first solution into the second (never the contrary) and take care that the prussiate solution is always preponderant. The Glauber’s salt is useful in rendering the precipitation of the blue pigment more complete by reason of the insolubility of the latter in saline fluids. When the blue sediment is all thrown down it is drained off on a filter, and repeatedly washed till a blue tint appears in the wash-waters, when it is dried for use. TURNBULL’S BLUE.--This is an old-fashioned name often applied, like the term Paris blue, to the violet shades of Prussian blue which have been prepared with red prussiate. =Ultramarine.=--According to Rowland Williams, F.C.S., natural ultramarine is, perhaps, the most beautiful blue pigment known. It was formerly, and is now to a small extent, manufactured (chiefly for artists’ use) from lapis lazuli, a blue mineral which occurs, intermixed with limestone and iron pyrites, in Siberia, Thibet, and China. In order to obtain ultramarine from lapis lazuli, the roughly pulverised mineral is ignited, dipped into vinegar to remove carbonate of lime, and then reduced to the finest possible state of division. The powder is next mixed with a cement composed of rosin, linseed oil, white wax, and Burgundy pitch, and the resultant paste is worked under water until all the ultramarine is separated. The ultramarine is washed several times with water, and afterwards with alcohol, which removes any of the resinous compound which may have adhered. When treated in this manner, lapis lazuli yields from 2 to 3 per cent. of ultramarine. According to Clement and Desormes, lapis lazuli has the following composition:-- Per cent. Soda 23·2 Alumina 34·8 Silica 35·8 Sulphur 3·1 Carbonate of lime 3·1 ----- 100·0