Group 2. All the silver present being as sumed to be removed in the first group, the mixed sulphides of Group 2 are washed until the wash water ceases to redden blue litmus paper, and are then boiled with a small quantity of nitric acid. Lead, bismuth, calmium and copper pass into solution in the form of nitrates, while mercury sulphide remains unchanged, and may be isolated by filtration. The, filtrate, con taining the mixed nitrates, is evaporated to a small volume, and sulphuric acid is added. This precipitates lead sulphate, which appears as a whitish precipitate, removable by filtration. The filtrate from this last operation may contain the nitrates of bismuth, cadmium and copper. If it is made alkaline by the addition of am monia water, any bismuth that it contains will be thrown clown in the form of the hydrate. The cadmium and copper nitrates are simul taneously reduced to the form of hydrates, which, however, remain in solution. Upon pass ing sulphuretted hydrogen through the solution containing them, a precipitate consisting of cad mium sulphide and copper sulphide is thrown down. If this is boiled with dilute sulphuric acid the copper sulphide remains unaffected, while the cadmium sulphide passes into solution. From the solution, sulphide of cadmium may be again thrown down by adding ammonia till the reaction is alkaline, and then passing sulphuret ted hydrogen through the solution. If cadmium is its sulphide is thrown down as a bright yellow precipitate.
Group 3. When the sulphidesof Group 3 have been isolated, some information may be had at once from the color of the precipitate. Thus arsenic sulphide is yellow, antimony sulphide is red and tin sulphide is black. If only one of these elements is present, it may therefore be detected by the color of its sulphide. If more than one are present, the mixed sulphides are treated with a solution of ammonium carbonate The sulphides of antimony and tin are unaffected, but the sulphide of arsenic passes into solution, and after filtration it may be again thrown down by the addition of hydrochloric acid. The mixed sulphides of antimony and tin are trans ferred to a porcelain dish, and heated with a small quantity of hydrochloric acid, to which a few crystals of chlorate of potash have been added. By this treatment they are reduced to the form of chlorides. The solution containing the mixed chlorides of antimony and tin should then be somewhat diluted, and a piece of plati num foil wrapped in zinc should be added. By the electrolytic action so set up, antimony and tin are thrown down, in the metallic state, upon the platinum foil ; and the foil will be blackened in spots, if antimony be present. In any case the foil should he washed and boiled with hydrochloric acid diluted with its own bulk of water. In this way any tin that may be present is brought into the form of the chloride, which dissolves; the antimony remaining unaffected. The presence of tin chloride in solution may be readily demonstrated by the addition of a solu tion of corrosive sublimate. The tin is thereby reduced to the form of a higher chloride, and a precipitate of Hg:C1, (calomel) is thrown down. If no tin is present, this precipitate is not formed.
Group 4. The metals of Group 4 are ob tained, in the general scheme of separation out lined above, in the form of sulphides and hy drates. The precipitate containing them is to be treated in a porcelain dish with cold dilute nitro-hydrochloric acid. The sulphides of nickel
and cobalt remain unaffected, and may be re moved by filtration, since the other metals pass into solution. The precipitate that is undis solved should be tested in a borax bead before the blowpipe. (See BLOWPIPE ANALYSIS).
Cobalt gives a blue bead, while nickel gives a reddish-brown one. If both metals are present, the color is intermediate between these two. In the reducing flame the reddish-brown color due to nickel changes to a gray, while the blue of the cobalt remains unaltered; hence the reducing flame should be tried, if no decided indication of cobalt is obtained in the oxidizing flame. For other and more exact tests for dis tinguishing cobalt from nickel, special treatises on qualitative analysis should be consulted. (For example, Scott's (Standard Methods of Chemical Analysis'). Nickel and cobalt being removed from the metals of Group 4 by the means indicated above, the filtrate contain ing the remaining members of the group is boiled until all the sulphuretted hydrogen is ex pelled. A little nitric acid is then added, and the solution is again boiled until the greater part of the acid is driven off, when the remain ing solution is diluted with water. The small amount of free acid that is still present is neutralized with sodium carbonate, care being taken that no permanent precipitate is formed. The solution is allowed to cool, barium car bonate is added in the cold and the whole is allowed to stand for 15 minutes. The precipitate contains the aluminum, chromium and iron in the form of hydrates, and also the excess of barium carbonate. The filtrate contains manganese and zinc. The precipitate is removed by filtration, dissolved in dilute hydrochloric acid, gently warmed and made alkaline by ammonia. By this process the hy drates of aluminum, chromium and iron are thrown down, free from barium. This precipi tate of the hydrates is collected on a filter, dried, transferred to a porcelain dish and dis solved in concentrated nitric acid. A few crys tals of potassium chlorate are then added, and the solution is boiled for several minutes. Upon adding sodium hydrate in excess, the iron is thrown down in the form of hydrate, the alu minum and chromium remaining in solution. The iron being removed by filtration, the filtrate is divided into two portions. One of these por tions is made acid with nitric acid, and am monia is added in excess. Aluminum hydrate is thrown down, if aluminum is present. The other portion of the filtrate is made acid with acetic acid, and lead acetate is added. If chro mium is present, a yellow precipitate of chro mate of lead, PbCrO., is thrown down. The filtrate from the treatment with barium car bonate, which may contain zinc and magnesium, is heated to boiling, and the barium that it con tains is completely precipitated with dilute sul phuric acid. Theprecipitate of barium sulphate is removed by filtration, and the filtrate is boiled, after addition of sodium hydrate in ex cess. If manganese is present, it is precipitated in the form of the hydrate, and may be removed by filtration. The filtrate from this operation is acidified with acetic acid, and treated with sul phuretted hydrogen gas. If zinc is present, it is thrown down in the form of a white precipi tate of zinc sulphide, ZnS.