The student having now ascertained to which group the basic radical of the simple salt under examination belongs, must proceed to discover which member of the group is present. The groups above given are almost identical with the subdivisions of the basic radicals described in Part I., the chief differences being the reversion of their order, and the division of the hydrosulphuric acid (Subdivision IV.) and sulphide of ammonium (Subdivision III.) groups respectively into two. The reason for reversing the order is obvious-it being far easier to separate at first those bodies which form the larger number of insoluble compounds, whilst, in the study of the reactions, it is simpler to begin with those bodies which yield the smallest number of insoluble salts. The student may now proceed to examine the precipitates belonging to the various groups, somewhat according to the following Tables, in each case referring to the reactions given in Chapter VI. for confirmatory tests. TABLE FOR GROUP I. The precipitate produced by hydrochloric acid may contain PbCl, AgCl, or Hg, Cl. Collect on a filter, transfer the precipitate to a large test-tube, and heat with much water: if it entirely dissolves, the solution will contain PbCl. The presence If a residue is left (it may be either AgCl or Hg, Cl), collect on a filter, remove to a test-tube, add NH HOˇand warm: if the residue dissolves entirely, AgCl. of lead must the solution will contain Pb2SO4 indicates Pb. The presence of silver must Ag. If a black residue is left, it will consist of (Hg)2O. The presence of mercury must be confirmed by collecting the precipitate, drying it at 100° C., and mixing it with Na,CO, and heating in a bulb-tube (see p. 169); a sublimate of grey globules indicates Hg. TABLE FOR GROUP II. The precipitate produced by hydrosulphuric acid may be Hg2S, Bi,S,, PbS, CuS, CdS, Pd,S, SnS, SnS2, Sb,S,, Sb,S,, As,S,, As,S *PS, *AuS, or S (if a ferric salt or chromate were present). Collect on a filter, transfer to a test-tube, and boil with (NH4)2S for five minutes: if a residue remains, it indicates * A separate examination must be made for platinum and gold, according to the plan given on page 245. TABLE FOR GROUP III. The precipitate produced by hydrate of ammonium may be UrH03, Fe, H2O, Cr,H,O,, or AlH,O,; it may also be a phosphate or fluoride of Ba, Sr, Ca, or Mg, or a phosphate of Ur, Fe, Cr, or Al. The oxalates will have been destroyed by ignition; and the borates do not occur. It will be sufficient to ascertain the presence of the phosphoric radical by dissolving a small portion of the precipitate in the least possible quantity of dilute HNO, in a watch-glass, adding a trace of NH HO, to neutralize as far as possible the excess of HNO, without reprecipitating the salt dissolved, and then introducing a few drops of AgNO,: the presence of H.PO, is ascertained by the immediate precipitate of the yellow Ag, PO The mass of the precipitate is then treated with sesquicarbonate of ammonium in the cold: complete solution indicates the presence of Ur2H,O,. Evaporate to dryness; dissolve the yellow residue in HA, and add K,Cfy: a brownish red precipitate or colour indicates Ur. If a residue is left, it is to be examined for Fe, Cr, or Al. Boil for five minutes with H,O, to separate Ba, Sr, and Ca as oxalates; filter, allow to cool, and add excess of KHO. TABLE FOR GROUP III. a. The precipitate produced by sulphide of ammonium may be Zn,S, Mn,S, Ni,S, or Co,S. Dissolve it in concentrated HCl, adding one or two drops of concentrated HNO, when boiling. To the solution add excess of KHO. Perfect solution indicates the presence of Zn,S: add HS to the solution, a white precipitate of ZnS indicates Zn. A precipitate of a flesh colour consists of Mn,S; a black precipitate, of NiS or Co2S. Dissolve in concentrated HCl, add excess of KĀ, and pass H2S gas: the non-formation of a precipitate indicates the presence of Mn,S. Confirm by the addition of NH HO, which will form NH HS, and give a fleshcoloured or buff precipitate of Mn,S, indicating Mn. The occurrence of a precipitate proves the existence of NiS, or CoS. Dissolve in concentrated HCl; add one drop of concentrated HNO, when boiling, then KCy in excess. Boil the solution, and acidify with dilute HCl : a precipitate indicates the presence of TABLE FOR GROUP IV. The absence of a pre- The precipitate produced by carbonate of ammonium, in the presence of NH HO and NH, Cl, may be Ba, CO, Sr2SO, or CaCO3. Dissolve in the smallest quantity of dilute HCI, add KCrO, in solution: the formation of a precipitate, after the lapse of a few minutes, indicates the presence of Ba. The absence of any precipitate indicates the presence of strontium or calcium. Divide the solution into two parts, dilute it with a small quantity of water. 1. Add a saturated solution of 2. If no precipitate occurs in 1. TABLE FOR GROUP V. If the various group-tests have produced no precipitate in the solution under examination, either NH,, Mg, K, or Na is present. Of these basic radicals, NH, will have been already detected in the preliminary examination (p. 391). Divide the solution into two portions, one being thrice the bulk of the other. Having now considered the method of detecting the basic radical in a simple salt, we proceed to give the details of SECTION II.-The examination for the acid constituent. The student must have already perceived that, although compound basic radicals are extremely rare, the compound acidradicals which occur in the course of analysis are very numerous. The latter bodies, though easily detected if they yield characteristic products of decomposition, are, however, in many cases recognized with great difficulty, particularly when of very great complexity. The recognition of the basic radicals by means of the blowpipe is comparatively easy, because in the majority of cases the acid-radical of the salt is expelled, or its basic constituent is left in combination with oxygen only as an oxide, the characters of which are easily recognized; but when we wish to detect the acid-radical present by the same means, the ready decomposability of the latter forms an insuperable obstacle. We have, however, at our disposal a method of Preliminary Examination which is of the greatest service in enabling us to form an idea concerning the nature of the acid-radical present, and occasionally, indeed, affording us decisive proof of its exist |