OF PHOSPHATES IN GROUP III. Table (419) after precipitating Groups I. and II., and a precipitate the latter in slight excess, to the HCl solution; it is then gently filtrate Am,S is added in excess and the solution boiled, then filtered, Transfer the two precipitates yielded by AmHO and Am,S to a porceExamine the precipitate by the following Table :— present Fe, Zn, Mn, Ni, Co, one or more were present as phosphates. Ba, Sr, Ca, Mg as phosphates; Fe, Zn, Mn, Ni, Co as sulphides; dilute HCl in a porcelain dish. If this does not dissolve it, drop dryness. Filter off S if necessary (note 1); then add a solution of Heat gently, and filter while hot : : Precipitate may consist of FePO4, AIPO4, CrPO4 (note 4). Dry the precipitate on the filter, and fuse it for a short time with finely powdered SiO2 and fusion-mixture, adding a little KNO3, in a platinum crucible or on platinum-foil. When cold, dissolve by boiling with a little distilled water, add Am2CO3, allow to stand for a short time, stirring occasionally; let the precipitate subside, filter: Filtrate: add HÃ until the solution is acid, boil for a short time, then add PbA2: yellow precipitate of PbCrO4. Presence of Cr, (as phosphate). Note. A white precipitate on addition of PbA2 may be disregarded. Precipitate may contain H4SiO4, Fe and Al as silicates, and Fe,Ho6. Acidify with HCl, evaporate to dryness, and heat the dry residue gently. Warm with a few drops of strong HCl, add hot water, and filter: Filtrate: add pure NaHO in excess, boil and Filtrate, acidify with (as Phosphate). Precipitate is brown Residue is SiO2 and may be neglected. a test-tube and warm gently; if no yellow precipitate forms even after standing be present in the solution, which may therefore be at once examined by Table filtrate and heated; if it causes no precipitate, (PO4)"" and therefore Ba, Sr, Ca, and once added, and the precipitate examined by Table III. c. (464, 465) or the may be examined either by adding AmCl, AmHO, and Am,S together and III. B. separately by AmCl and AmHO and then Am,S, and examining the pre by boiling with excess of NaHO, and filtering; AlPO4 will be in solution, and is gelatinous precipitate; Fe,Ho, remains as a precipitate and is detected by dissolv B. b. THE SUBSTANCE POSSESSES METALLIC LUSTRE, AND IS PROBABLY A METAL OR ALLOY. After making the Preliminary Examination in (467-469), either of the two methods given below (470, 471) may be adopted. The first method is by far the most ready and certain for the examination of a metal or alloy of unknown composition, since all metals, even when present in small quantity only, may thus be detected. In making the solution by the second method, Sn, Sb, Au, and Pt are left undissolved, all other metals passing into solution; it is not however to be recommended as a general process for examination of metals and alloys, since the following complications are apt to occur :-If As is present with Sn, a part or the whole of the As may remain in the residue; Pt, if present with a sufficient quantity of Ag, may pass entirely into solution; and Sb will always partly dissolve. The process however is useful in cases where an alloy, known to contain a large proportion of Sn or Sb, has to be examined for other metals, which are thus dissolved away at once from the bulk of the Sn or Sb: but care must be taken that As is not passed over in the presence of Sn. PRELIMINARY EXAMINATION. 467. Note its colour, and smell, if any, when rubbed with the hand; also whether it is crystalline or not. Note also the hardness of the metal, by seeing if it can be scratched or cut by a steel knife; also whether on being struck smartly with a hammer it breaks to powder (brittle), or flattens out (malleable). Then try the following experiments: Experiment. 468. I.-Heat a small portion on 469. II.-Heat a portion in a small The results obtained by (403) The inference will be found A yellow sublimate melting to Presence of Hg, Cd, As, Presence of S. from a sulphide. PROCESSES FOR SOLUTION AND EXAMINATION OF A METAL OR ALLOY. 470. METHOD I.-Pour some rather dilute HCl upon the powdered metal in a small flask covered with a watch-glass with its concave surface upwards, and heat for some time just short of boiling; if the metal dissolves readily, continue heating until the metal is completely dissolved, and examine the HCl solution according to the General Table (419). Frequently HCl alone does not effect complete solution, two or three drops of strong HNO3 should then be poured in, and more HNO, and HCl added occasionally when the action ceases or when red fumes are no longer given off. When the metal has entirely disappeared, add a little more strong HCl and boil as long as any Cl or reddish fumes are given off; then dilute with a little water, heat to boiling, and cool; filter if there is any white residue : Residue, if crystalline, is probably PbCl,, and will be found to dissolve entirely if washed with sufficient boiling water. In this solution the presence of Pb is confirmed by adding | K,CrO4, which gives a yellow precipitate soluble in excess of KHO: Presence of Pb. Filtrate (note 1): dilute largely with H2O (see note 2), and whether this causes a precipitate or not, pass H2S to saturation into the solution; examine any precipitate thus produced by Table II. (435), and proceed to examine the filtrate for Groups III., IV., and V., as directed in the General Table (419). If any residue is left after washing well with boiling water, it is pro- Note 1.-If Au and Pt may be bably AgCl; confirm the pre-present, they must be tested for in sence of Ag by pouring upon the the HS precipitate, according to residue hot AmHO, it dissolves the directions in (472-474). completely but is reprecipitated on adding HNO3 in excess :Presence of Ag. Note 2.-A white precipitate appearing on dilution is due to the presence of Bi, Sb, or Sn. 471. METHOD II.-Pour upon the finely divided metal some strong HNO3,* and heat in a small flask covered with a * If Hg is found in the preliminary examination and small quantities of Ag have to be tested for, the Hg should be expelled by heating the substance strongly in a porcelain crucible before dissolving in acid, as Hg (NO3)2 tends to prevent the precipitation of Ag by HCl in Group I. watch-glass as long as any red fumes appear. One of two results will occur : Note 1.-The solution is liable to contain small quantities of these metals, which must always be tested for in a careful analysis. Note 2.-BiOCl will often precipitate on dilution, but the precipitate will disappear on adding HCl and boiling, being thus easily distinguished from the Group I. precipitate. Note 3.-If much residue is obtained a small quantity of it may be heated in a test-tube with HCl adding KC1O,, if it dissolves entirely dissolve the whole of the residue, then examine the solution by Table II., commencing at (435b): if it refuses to dissolve proceed with the rest of the residue as directed below. If the residue is small in quantity examine it at once as directed below. Examination of the Non-metallic Residue insoluble in HNO-Dry the residue on the filter at a gentle heat, mix it thoroughly with about an equal quantity of powdered Na,CO, and NaNO,, and fuse the mixture in a porcelain crucible for some time; then pour the melted substance out into a porcelain dish; allow it to cool, and pour upon it cold water; let it stand for some time. After crushing the mass with a pestle and stirring it occasionally, filter, and wash the residue on the filter with dilute alcohol, throwing away the washings: Residue may contain Sn, Sb, Pt, Au. Place it in a small porcelain dish, pour in a little HCl and heat, then add water; whether the residue has dissolved or not place in the liquid a slip of Pt-foil and drop upon it a piece of pure Zn; H-gas is given off; wait until this ceases, taking care that there is some Zn left undissolved, and adding more Zn if the first piece has entirely dissolved. Now remove the platinum strip; if it is stained black Sb is present. The residue in the dish may consist of Sn, Au, and Pt; remove the Zn, rinsing off any substance adhering to it into the dish, stir the liquid in the dish well, then pour off the liquid, carefully leaving the residue; pour in water, stir well, and again pour off carefully. Boil the residue for some time with strong HCl in a testtube, dilute, decant, add HgCl2, a white precipitate forms:-Presence of Sn. Residue dissolve by warming with HCl and HNO3, and examine the solution for Au and Pt by (474), using only the left hand portion. Filtrate may contain (AsO4): add HNO3 until the solution is acid and boil, evaporating the liquid in a dish if very bulky. Pour in AgNO3 as long as it gives any precipitate, and add gradually AmHO diluted with 10 or 12 times its bulk of water, a brown precipitate shows:-Presence of As. SEPARATION AND DETECTION OF Au AND Pt. 472. Au and Pt will, in the ordinary course of analysis, be entirely precipitated as sulphides in the Second Group, if HS is passed for some time into the hot HCl-solution; and since these sulphides are soluble in KHO and in Am,S, on examining the HS precipitate by Table II. (435), the Au and Pt will pass into the filtrate when the precipitate is boiled with KHO or Am2S. No modification of the process described in Table II. is required for the detection of these two metals until the examination of the residue in the hydrogen-flask is commenced. The Au and Pt will be present in this residue, associated with Sn if it be present, and usually also with at least a part of the Sb (if present), since Zn and Pt if in contact in an acid liquid cause the separation of metallic Sb (193). Accordingly when Au and Pt have to be tested for, the ordinary course of analysis is to be followed until the residue in the hydrogen-flask is obtained; and this is examined as directed below (473). |