Alumina in a state suitable for the preparation of the pigments known as “lakes” may be produced in the following manner:--Dissolve 1 lb. of alum in ½ gallon of water, and add 75 grains of sulphate of copper, and about ¼ lb. of zinc turnings; leave the mixture for three days in a warm place, renewing the water lost by evaporation. The copper is first deposited upon the zinc, the two metals thus forming a voltaic couple sufficiently strong. Hydrogen is disengaged, sulphate of zinc is formed, and the alumina gradually separates in the state of a very fine powder; the action is allowed to continue until there is no more alumina left in solution, or until ammonia ceases to give a precipitate. If the reaction is prolonged beyond this point, oxide of iron will precipitate if present. The alumina washes easily, and does not contract upon drying. BRAZIL-WOOD LAKE.--(_a_) Digest 1 lb. ground Brazil-wood in 4 gal. water for 24 hours, boil ½ hour, and add 1½ lb. alum dissolved in a little water; mix, decant, strain, add ½ lb. tin solution, again mix well, and filter; to the clear liquid cautiously add a solution of carbonate of soda while a precipitate forms, avoiding excess; collect, wash, and dry. The shade will vary according as the precipitate is collected. (_b_) Add washed and recently-precipitated alumina to a strong filtered decoction of Brazil-wood. CARMINATED LAKE.--(_a_) The cochineal residue left in making carmine is boiled with repeated portions of water till exhausted; the liquor is mixed with that decanted off the carmine, and at once filtered; some recently-precipitated alumina is added, and the whole is gently heated, and well agitated for a short time. As soon as the alumina has absorbed enough colour, the mixture is allowed to settle, the clear portion is decanted, and the lake is collected on a filter, washed, and dried. The decanted liquor, if still coloured, is treated with fresh alumina till exhausted, and thus a lake of second quality is obtained. (_b_) To the coloured liquor obtained from the carmine and cochineal as just stated, a solution of alum is added, the filtered liquor is precipitated with a solution of carbonate of potash, and the lake is collected and treated as before. The colour is brightened by addition of tin solution. CARMINE.--Boil 1 lb. cochineal and 4 dr. carbonate of potash in 7½ gal. water for ¼ hour. Remove from the fire, and stir in 8 dr. powdered alum, and allow to settle for 20 to 30 minutes. Pour the liquid into another vessel, and mix in a strained solution of 4 dr. isinglass in 1 pint water; when a skin has formed upon the surface, remove from the fire, stir rapidly, and allow to settle for ½ hour, when the deposited carmine is carefully collected, drained, and dried.