As silica and titanic acid are the only two substances that produce a clear bead, the student, if he gets a clear bead, may almost conclude that he is experimenting with silica, titanic acid being a rare substance. When soda is heated with silica, a slight effervescence will be the first phenomenon noticed. This is the escape of the carbonic acid of the carbonate of soda, while the silicic acid takes its place, forming a glass with the soda. As titanic acid will not act in the same manner as silica, it can be easily distinguished by its bead not being perfectly pellucid. If the bead with which silica is fused should be tinted of a hyacinth or yellow color, this may be attributed to the presence of a small quantity of sulphur or a sulphate, and this sometimes happens from the fact of the flux containing sulphate of soda. The following metals, when exposed with carbonate of soda to the reducing flame, are wholly or partially reduced, viz. the oxides of all the noble metals, the oxides and acids of tungsten, molybdenum, arsenic, antimony, mercury, copper, tellurium, zinc, lead, bismuth, tin, cadmium, iron, nickel, and cobalt. Mercury and arsenic, as soon as they are reduced, are dissipated, while tellurium, bismuth, lead, antimony, cadmium, and zinc, are only partially volatilized, and, therefore, form sublimates on the charcoal. Those metals which are difficult of reduction should be fused with oxalate of potassa, instead of the carbonate of soda. The carbonic oxide formed from the combustion of the acid of this salt is very efficient in the reduction of these metals. Carbonate of soda is very efficient for the detection of minute quantities of manganese. The mixture of the carbonate of soda with a small addition of nitrate of potassa, and the mineral containing manganese, must be fused on platinum foil. The fused mass, when cooled, presents a fine blue color. * * * * * 1. The following minerals, according to Griffin, produce beads with soda, but do not fuse when heated alone: quartz, agalmatolyte, dioptase, hisingerite, sideroschilosite, leucite, rutile, pyrophyllite, wolckonskoite. 2. The following minerals produce only slags with soda: allophane, cymophane, polymignite, æschynite, oerstedtite, titaniferous iron, tantalite, oxides of iron, yttro-tantalite, oxides of manganese, peroxide of tin (is reduced), hydrate of alumina, hydrate of magnesia, spinel, gahnite, worthite, carbonate of zinc, pechuran, zircon, thorite, andalusite, staurolite, gehlenite, chlorite spar, chrome ochre, uwarowite, chromate of iron, carbonates of the earths, carbonates of the metallic oxides, basic phosphate of yttria, do. of alumina, do. of lime, persulphate of iron, sulphate of alumina, aluminite, alumstone, fluoride of cerium, yttrocerite, topaz, corundum, pleonaste, chondrodite.