PRELIMINARY EXAMINATION-continued. Observation or experiment to be made. VI. Make a clear borax bead in a platinum wire loop (31); dip it into a small quantity of the liquid contained in a watch-glass, then fuse it in the outer and inner blowpipe flames; observe the colour of the bead carefully both whilst hot and when cold. VI a. Confirmatory — The presenee of Cr. and Mn may be con Result of observation or experiment. Inference to be drawn from the result. The bead is colourless both hot and cold, after Absence of the metals having been heated in both flames The bead is coloured: In outer flame. purple, hot; light In inner flame. Grey or black and cold. A yellow mass on cooling (105) firmed, if detected A bluish-green mass on cooling (119) by the borax bead, by moistening a below. mixture of a little solid Na2CO3, and KNO3 on platinum foil with a few drops of the original solution, drying by gently heating it at a short distance above the flame, and then fusing by directing the blowpipe flame on the lower surface of the foil. EXAMINATION FOR THE METAL. 335. If the original liquid leaves a residue on evaporation (334, III.), and is neutral or acid to litmus-paper (334, II.), examine as directed under I. (336 et seq.); if it is alkaline work by II. (359). The method of analysis given below will be best understood by a reference to the Table of Analytical Classification of the metals (pp. 168, 169): the list of metals possibly present, which is entered here at the head of each Group Table, will be seen to correspond with the groups in that table. * If the solution is very dilute, a portion of it should be evaporated nearly to dryness in a small porcelain dish before the bead is dipped into it; if after dipping the bead once and fusing, no colour is seen, it should be wetted once more with the solution and dried in the flame, and this process should be several times repeated before again fusing the bead. † Cr, if present as a chromate, gives a bead brown while hot after having been fused in the outer blowpipe flame, but becoming permanently green in both flames after having been heated in the inner flame. I. THE LIQUID IS NEUTRAL OR ACID TO LITMUS. 336. Examination for Group I. (Pb, Ag, Hg').—To a portion of the liquid add HCl in excess (35 a), and note any change which occurs (see note 1). If a white precipitate forms,* add more HCl and heat for a moment to boiling, then cool at once: if any precipitate remains, work as directed under the left-hand column; if no precipitate remains, refer to the right-hand column (note 2). A white precipitate forms (see note 3), and is either not dissolved when boiled | No precipitate forms, with HCl, or dissolves and reappears on cooling the liquid (showing the Presence of Pb). The precipitate may consist of AgCl, PbCl2, Hg2Cl2. Let the precipitate settle and decant the liquid (see note 4): boil the precipitate in the test-tube with AmHO (see note 5): 1. The precipitate dis- 2. The precipitate does not dissolve:- Presence of Ag. Confirm by adding excess of HNO3 to the AmHO solution, a milkiness appears: Presence of Ag. Note. Coagulated AgCl often dissolves only slowly in AmHO. The colour of the precipi- The precipitate becomes Presence of Pb. Presence of Pb. black:- white and or a precipitate forms in the cold, but disappears on boiling after addition of more HCl, and does not reappear on cooling the liquid:Absence of Ag, and probably of Pb and Hg. Note 1.-Effervescence may be noticed on the addition of HCl, owing to certain gases being evolved, a list of which will be found in (349) : some of them are readily detected by their smell or colour, but special tests need not be tried, as they will be afterwards used in the Preliminary Examination for acid-radicles (345 et seq.): the fact that a gas is evolved should however always be noted down, even if the nature of the gas is not ascertained. A yellow liquid whose colour is due to the presence of a neutral chromate turns reddish-yellow on addition of HCl : this confirms the presence of a chromate. Note 2.-A white precipitate which disappears on boiling after addi tion of more HCl, and does not reappear on cooling, may consist of BiOCl or Sbocl. A little of the milky liquid produced by the first * Yellow S may separate from a theiosulphate (see 349, 2): this pre cipitate requires no further examination. addition of HCl should be mixed with H,T solution, if the precipitate consists of SbOCl it will disappear, BiOCl is not thus dissolved. Note 3.-A colourless, gelatinous precipitate of hydrated SiO, may form here confirm the presence of SiO, by evaporating a portion of the original solution to dryness with HCl, and warming the residue with HC1: a residue insoluble in HCl proves the presence of SiO2; filter or decant from the residue of SiO2, and employ the HCl solution to detect the metal present by (337 et seq.) Note 4.-In this and all subsequent places where decantation of the liquid is recommended, it should be understood that a precipitate will usually settle if the liquid is well shaken or heated and allowed to stand for several minutes. (See 23 b.) Note 5.-In case the liquid cannot be completely decanted, add the AmHO in excess to the liquid in which the precipitate is suspended. 337. Examination for Group II. (Hg, Pb, Bi, Cu, Cd, Sn, As, Sb). To the above portion of the solution, made acid with HCl and boiled until free from Cl or SO, if these gases are evolved on heating, add water; a milkiness due to precipitation of BiOCl or SbOCl may result, SbOCl being distinguished from BiOCl by a few drops of the liquid becoming clear on addition of HT solution. Whether a milkiness has been produced or not by water, add strong H,S-water or pass HS until the liquid after having been well shaken smells strongly of the gas, and heat gently (see note 1 below): if no precipitate forms, heat to boiling, since Sn (as stannicum) and As (as arsenicum) are only precipitated by HS on boiling; if a precipitate has formed examine it by the following Table; if none has appeared, or only a white milkiness due to precipitation of sulphur (see note 2 below), the absence of Hg, Pb, Bi, Cu, Cd, Sn, As, and Sb is proved: pass on to (338). Note 1.Certain changes in the colour of the precipitate may be noticed if the H2S is slowly added: thus Hg" gives a precipitate which is at first white, then yellow, brown, and ultimately black; Pb, in strongly-acid solutions, gives a red precipitate, becoming black on addition of water and more H2S. Note 2.-Characteristic changes of colour of the solution often accompany the separation of sulphur; thus A reddish-yellow solution changing to pale green indicates a ferric salt. chromate. A reddish-yellow manganate. permanganate. The precipitated S need not be examined. Note the colour of the precipitate yielded by H2S, and examine it according to 1, 2, or 3, below: 1. The precipitate is dark-brown or black; it may consist of SnS, CuS, HgS, Bi2S3, PbS. Add pure NaHO in excess to the liquid and precipitate, or to the precipitate alone after decanting the liquid if possible (see note 4, p. 180), and boil: The precipitate dis- The precipitate does not dissolve: it may consist of CuS, HgS, Bi2S3. PbS. a. The original solution is blue or green, and becomes intensely blue on addition of excess of AmHO:-Presence of Cu. Confirm by adding a few drops of H2SO4 to the original solution, and dipping into it a bright knife blade or piece of steel, a red film of Cu deposits:-Presence of Cu. Note. To detect small quantities of Cu the K4Cfy test (in 163) should be used. B. The original solution is colourless. Test in separate portions for Hg, Bi, Pb by the following special tests: 2. The precipitate is yellow: it may consist of CdS, As2S3, SnS2:- The precipitate does not dissolve: it is bright yellow and pulverulentPresence of Cd. The presence of Cd may be confirmed by showing that the precipitate produced by H2S dissolves on being boiled with dilute H2SO4.] The precipitate dissolves: it may consist of As2S3 or SnS2; examine portions of the original solution as directed below: Acidify a portion with HCl, and place in Presence of Sniv. Acidify a portion with strong HCl, immerse in it some pieces of bright Cu and boil, a black film is deposited on the Cu: Presence of As. Note. If the yellow precipitate formed by H2S appeared at once in the cold, the As is present as Arsenosum; if it formed only on boiling, Arsenicum is present. 3. The precipitate is orange-red: it may consist of Sb2S3. Confirm by acidifying a portion of the original solution with HCl, and immersing in it a piece of Zn resting on a slip of platinum-foil, a black stain on the platinum (193):— Presence of Sb. Note.-It occasionally happens, if the solution has not been sufficiently diluted, that H2S gives a reddish precipitate with Pb-solution; such a precipitate, however, becomes black on adding more H2S-water. 338.-Examination for Group III. (Al, Fe, Cr; Zn, Mn, Ni, Co; Ba, Sr, Ca, Mg as phosphate, fluoride, or oxalate; BaCro1). Caution. It is of the greatest importance to remember that if an organic salt-more especially a tartrate—has been detected in the preliminary examination, and it has not been proved to be a salt of Ba, Sr, Ca, Mg, K, or Na, and must therefore be a salt of one of the metals of Group III., the detection of the metal by the directions given below may be hindered or prevented. It is therefore necessary to destroy the organic acid-radicle by evaporating some of the substance to dryness after adding a little strong HNO, and then gently igniting the residue. The residue, when cool, is dissolved by warming with a few drops of HCl, the solution diluted and this solution is to be substituted for the original solution in the examination for Group III. To another portion of the original solution add first AmCl solution, then AmHO in excess; note carefully the colour and appearance of any precipitate (which is probably due to Al, Fe or Cr, but if white or nearly so may be a phosphate, oxalate, &c.), or the colour of the liquid if no precipitate forms (Ni yields a violet coloured liquid); then whether a precipitate has been produced or not, add Am2S or better H2S, and boil. (See note below.) Note.-If no precipitate forms on addition of AmCl and AmHO, or of Am,S, until the liquid is boiled, when a pale-green precipitate is produced, this precipitate is due to the presence of a chromate, which will have been already detected by the liquid turning from yellow to green on addition of H2S. The pale green precipitate need not be further examined, but its formation should be noted as confirmatory of the presence of a chromate. Proceed to examine for the metal present by (342). If a precipitate forms examine it by the table below.* If * White S, separated from the Am,S by the action of a ferricyanide or other oxidiser, may here render the liquid milky: it is recognised by |