Note. -The evaporation to dryness with HCl removes HBO,* and HF, which volatilise, whilst H,SiO, is left insoluble in HCl and therefore remains as an insoluble powder on afterwards warming with HC; this residue of SiO, also remains however if HF was present, being caused by the corrosion of the dish; since however HF if present has already been found, no notice will then be taken of the residue. 342. Examination for Group IV. To a portion of the original solution add AmCl, AmHO in excess, and then Am,CO, solution; warm gently:— forms:Absence of Ba, Sr, Ca. A white precipitate forms, which may consist of No precipitate BaCO3, SrCO3, CaCO3. Heat and filter, or let stand for a time and decant: dissolve the precipitate by pouring upon it a little hot dilute HCl, Pass on to (344). and proceed to examine the solution by (343). 343. Dip a loop of platinum wire into the HCl solution, and hold the wire in the Bunsen flame. If the flame coloration thus obtained is not decisive, employ the tests placed at the foot of each column as confirmatory : A red flame, appearing dingy-green through the indigo-prism:— Presence of Ca. Confirmatory.--Add CaSO4 To another portion add Presence of Ca. *Several evaporations are necessary in order to remove HBO, entirely if it is present in large quantity; but its presence interferes only with the flame colorations of Ba, Sr, and Ca, and not with the liquid tests, and is therefore not of serious consequence. A brilliant green coloration may be seen following a yellowish-green or red coloration, it is due to the presence of HBO. 344. Examination for Group V. To the liquid, in which Am,CO, has produced no precipitate, add Na,HPO4, and if a precipitate does not form at once warm the liquid gently, shake or stir it well, and let it stand for some time: a white crystalline precipitate shows presence of Mg. If no precipitate forms even after standing, Mg is absent; proceed to (345). 345. Into a portion of the original solution, acidified (if not already acid) with HCl, dip a loop of platinum wire, and hold it in the Bunsen flame; if no distinct coloration is obtained, boil down some of the original solution in a porcelain dish nearly to dryness, add a few drops of HCl, and again try the flame coloration :— flame: which shows no red or violet colour through the indigo-prism: Presence of Na. A pale violet flame (sometimes tinged yellow by a Intense yellow trace of Na), which appears violet or red through the indigo-prism:-Presence of K. Confirm by stirring some of the original solution, boiled down if very dilute, with PtCl and a few drops of HCl a yellow precipitate shows presence of K. Addition of alcohol much aids the formation of the precipitate. [NaHT may be substituted for PtCl, as being more economical.] Note. If the preceding examination has not detected a metal, no commonly occurring metal can be present in any quantity. EXAMINATION FOR THE ACID-RADICLE IN A SOLID 346. Several acid-radicles will usually have been already detected during the examination for the metal. Thus, on acidifying with HCl and warming (336) the acid-radicles mentioned in (349) would be detected. 346a. On adding HS-water and warming (337), the following acid-radicles will have been detected by the fol 4 'MnO4: a purple so- "SnO3 a dingy - yellow precipitate, usually forming only when heat is applied. "AsOg: a bright-yellow precipitate, forming at once in the cold. "AsO4: a bright-yellow precipitate, forming at once if the liquid is boiled; but only after a long time in the cold solution. "SbO4: an orange-red precipitate. Also PO BO3, F, O, SiO,, may have been detected, if in combination with Ba, Sr, Ca, or Mg (339-341). If any one of the above acid-radicles has been found and confirmed by a special test, together with the metal with which it is combined, any further examination for an acidradicle is unnecessary. If no acid-radicle has yet been found, proceed according to (347 et seq.) 347. Since the metal present has been detected already, the examination for the acid-radicle may be usually much simplified by considering the solubility in water or in acids of the different saline compounds of this metal. Thus a salt of the metal which is insoluble in water cannot possibly be present in a neutral solution; a salt insoluble in water and acids cannot be present in a liquid with either acid or neutral reaction. A reference to the Table of Solubilities (455–458, p. 252) will thus frequently limit very considerably the number of acid-radicles that can possibly be present; and in cases where this number is very small, the analyst may dispense with the full analytical course drawn out below, and proceed at once to detect the acid-radicle by trying special tests for those acid-radicles only which can possibly be present. PRELIMINARY EXAMINA 348. Pour dilute H2SO4 in excess upon the substance in a test-tube, 349. A gas is evolved, shown by the occurrence of effervescence or 350. Add strong H2SO4 in small quantity to a fresh portion of the of the results enumerated below occurs;* if none of them is noticed 3. Acid fumes are given off, but the liquid is not coloured: drop in some small pieces of Cu and heat to boiling, reddish-brown fumes are evolved: Presence of a nitrate. Confirmatory.—Add to the liquidt in a test-tube about an equal volume of strong H2SO4, cool thoroughly, then pour a little strong FeSO4 solution gently down the inside of the tube so as to form a distinct layer on the surface of the acid liquid, a brown ring at the surface of contact of the two layers shows Presence of a nitrate. 351. After heating the tube containing the strong H2SO4 and subthoroughly; if it is seen to be corroded and dimmed :-Presence of a here, requires no confirmation. * If Pb, Ba, Sr, or Ca is present the addition of H2SO4 causes a precipitate of the may be disregarded. Obtained by boiling the substance if a solid with water, and filtering or decant |