YELLOWS. Chrome Yellow.—(a) Add a filtered solution of nitrate or acetate of lead to a filtered solution of neutral chromate of potash so long as a precipitate falls ; collect this, wash with snit wster, aud dry in security from sulphur-tainted air. et) Dissolve acetate of lead in warm water, and add sufficient sulphuric acid to convert it into sulphate ; decant the clear liquid, wash the residue with soft water, and digest with agitation in a bet solution of yellow (neutral) chromate of potash, containing 1 part of this salt for every 3 parts sulphate of lead ; decant the liquid, and drain, wash, and dry the precipitate.
(fambaic (Fn., Gommc Gutte ; GER., Gutti, Gummijutt).— Gamboge is a product of several trees of E. Asia: viz., Garcinia Morella var. 0. pedi,ellata [G. Hanburyi2, a native of Cambodia, the province of Chantibun in Siam, the Wands ou the E. coast of the Gulf of Siam, aud the S. parts of Cochin China ; G. Morella, growing in the moist forests of Ceylon and S. India; and G. pictoril, of S. India, by some considered identical with G. Morella. G. travancorica, of the aouthern forests of Travancore and the Tinnovelly Ghfits, is capable of affording small supplies of the pigment for local use, but not for export. (See also Resinous and Gummy Substances—Gamboge.) When the raday season has set in, parties of natives start in search of gamboge-trees, and select those which are sufficiently matured. A spiral incision is mado in the bark on two sides of the tree, and joints of bamboo are plueed at the base of the incision so as to catch the gum-resin as it exudes with extreme slownesa during a period of several months. It iasues aa a ellowish fluid, but gradually assumes a viscous and finally a aolid atate in the bamboo receptacle. It is very commonly adulterated with rice-flour, and the powdered bark of the tree, but the latter imparts a greenish tint. Sand is occasionally added. The product from a good tree may fill three bamboo joints, each 18-20 in. long and in. in diameter. The trees flourish on both high and low land. Annual tapping ie said to shorten their lives, but if the guln-resin is only drawn in alternate years, the trees do not seem to suffer, and last for many years. Dr. Jamie, of Singapore, who has gamboge
trees growing on his estate, says that they flourish most luxuriantly in the dense jungles. He considers tbe best time for cutting to be February-April. The filled bamboos are rotated near a fire till the moisture in the gamboge has evaporated sufficiently to permit the bembee to be atripped from the hardened gum-resin. The gamboge is secreted by the tree chiefly in numerous ducts io the middle layer of the bark, bestides a little in the dotted vessels of the outermost layer of the wood, and in the pith. It arrives in commerce in the form of cylinders, 4-8 in. long and 1-2i in. in diameter, often more or less rendered shapeless. When good, it is dense, homogeneous, brittle, shaming conchoidal fracture, scarcely translucent, and of rich brownish-orange colour. Inferior qualities show rough, granular fracture, and brownish hue, and are sometimes still soft. The pigment consists of a mixture of 15-20 per cent. gum with 85-80 per cent. resin. It reaches Europe from Cambodia by way of Bangkok, Saigon, and Sing,apore. The exports from Singapore in 1877 were 240 picas (of 1331 lb.); from Bangkok in 1875, 346 piculs; from Saigon annually, 30-40 piculs. Saigon, in 1879, received 27 picu/s, valued at 12/. a cwt., from Cambodia.
Naples Yellow,—(a) Mix 3 lb. powdered metallic antimony, 1 lb. oxide of zinc, and 2 lb. red-lead ; calcine, grind fine, and fuse in a cloaed crucible; grind the fused mass to fine powder, and wash well. (b) Grind I part washed antimony with 2 parts red-lead to a stiff paste with water, and expoae to red heat for 4-5 hours.
Olpiment or King's Yellow and Realgar.—See pp. 339-340.
Yellow Lakes.—(a) Boil 1 lb. Persian berries, quercitron-bark, or turmeric, and 1 oz. cream of tartar, in 1 gal. water till reduced to half ; strain the decoction, and precipitate by solution of alum. (6) Boil 1 lb. of the dyestuff with lb. alum ia 1 gal. water, and precipitate by solution of carbonate of potash. (c) Boil 4 oz. annatto and 12 oz. pearlash in 1 gal. water for hour ; strain, precipitate strain, and dry.