STAINED GLASS. Under the head of GLASS PAINTING this sabject has been already noticed. The following details are additional. The blues of vitrified co lors are all obtained from the oxide of cobalt. Cobalt ore (snlphuret ) being well roasted at a dull red heat, to dissipate all the sulphur and arsenic, is dissolved in somewhat dilute nitric acid, and after the addition of much water to the saturated solution, the oxide is precipitated by car bonate of soda, then washed upon a filter, and dried. The powder is to be mixed with thrice its weight of saltpetre ; the mixture is to be deflagrated in a crucible, by applying a red-hot cinder to it, then exposed to the heat of ignition, washed, and dried. Three parts of this oxide are to be mixed with a flux, consisting of white sand, borax, nitre, and a little chalk, sub jected to fusion for an hour, and then ground down into an enamel powder for use. Blues of any shade or intensity may be obtained from the above, by mixing it with more or less flux.
The beautiful greenish yellow, of which color so many ornamental glass vessels have been lately imported from Germany, is made in Bohemia by the following pro cess. Ore of uranium, uran-ochre, or uran-glimmer, in tine powder, being roasted, and dissolved in nitric acid; the filtered solution is to be freed from any lead present in it, by the cautious addi tion of dilute sulphuric acid. The clear green solution is to be evaporated to dry ness, and the mass ignited till it becomes yellow. One part of this oxide is to be mixed with 8 or more parts of a flux, consisting of 4 parts of red lead and 1 of ground flints ; the whole fused together and then reduced to powder.
Chrome green.—Triturate together in a mortar equal parts of chromate of potash and flowers of sulphur; put the mixture into a crucible and fuse. Pour out the fluid mass; when cool, grind and wash well with water to remove the snlphuret of potash and to leave the beautiful green oxide of chrome. This is to be collected upon a filter, dried, rubbed down along with thrice its weight of a flux, consist ing of 4 parts of red lead and 1 part of ground flints fused into a transparent glass ; the whole is now to be melted and afterwards reduced to a fine powder.
Violet.—One part of calcined black ox ide of manganese, one of zaffre, ten parts of white glass pounded, and one of red lead, mixed, fused, and ground. Or gold
purple (Cassius's purpleprecipitateN with chloride of si lver previously fused, with ten times its weight of a flux, consisting of ground quartz, borax, and red lead, all melted together ; or, solution of tin being dropped into a large quantity of water, solution of nitrate of silver may be first added, and then solution of gold in aqua i reqia, in proper proportions. The preci pitate to be mixed with flux and fused. STARCH is a white pulverulent sub stance, composed of microscopic sphe roids, which are bags containing the amylaecous matter. It exists in a great many different plants, and varies merely in the form and size of its microscopic particles ; as found in some plants, it consists of spherical particles of an inch in diameter ; and in others of ovoid particles of or of of an inch. It occurs-1, in the seeds of all the acotyle dinous plants, among which arc the seve ral species of corns, and those of other graminece i 2, in the round perennial tap roots, which shoot up an annual stem ; in the tuberose roots, such as_potatoes, the Convoleulue batatas and edulis, the Reliant/las tuberosus, the ,Tatropha maui hot, &c., which contain a great quantity of it ; 3, in the stems of several monoco tyledinous plants, especially of the palm tribe, whence sago comes ; but it is very rarely found in the stems and branches of the dicotyledinons plants ; 4, it occurs in many species of lichen. Three kinds of starch have been distinguished by chemists ; that of wheat, that called is line, and lichen starch. These three agree in being insoluble in cold water, alcohol, ether, and oils, and in being con verted into sugar by either dilute sul phuric acid or diastase. The main differ ence between them consists in their habi tudes with water and iodine. The first forms with hot water a mucilaginous so lution, which constitutes, when cold, the paste of the laundress, and is tinged blue by iodine ; the second forms a granular precipitate, when its solution in boiling hot water is suffered to cool, which is tinged yellow by iodine; the third affords, by cooling the concentrated solution, a gelatinous mass, with a clear liquor float ing over it, that contains little starch.