The solution containing the ZnNa,O, is filtered, and the Zn is precipitated by passing HS gas through it.

ZnNa,O2+2H,S=ZnS + Na,S+ 2H2O

The hydrates of Mn, Ni and Co are then converted into chlorides by treating them with dilute HCl. The solution is nearly neutralised with NH,OH, and an excess of (NH)CH2O, is added, which converts the MnCl2 into the acetate, from which solution MnS is not precipitated by passing HS gas.

MnCl,+2(NH)C H,O,=Mn(C,H,O,),+2NH,CH

3

The solution of Mn(CHO), is then filtered off from sulphides of Ni and Co, and the Ma is precipitated as carbonate by the addition of Na,CO. Mn(C2H2O2)2 + Na ̧CO2 = MnCO ̧ + 2NaC2H ̧O2.

3

The NiS and CoS are converted into chlorides by treating with HCl and KCIO; Cl is boiled off, and the excess of acid is neutralised by the addition of NaCO3. An excess of KCN solution is then added, forming double cyanides of Ni and Co.

NiCl2 + 4KCN = 2KCN.Ni(CN)2 + 2KC1
CoCl2 + 6KCN = 4KCN.Co(CN)2 + 2KC1

To the solution containing the double cyanides is added an excess of NaOH and then Br water, which precipitates the Ni as the hydrated sesquioxide and oxidises the potassium cobalto-cyanide into the potassium cobalti-cyanide.

4

2

2K,Ni(CN), +2NaOH + Br2+ 4H,O= Ni(OH), +4KCN + 2NaBr + 4HCN 2K,Co(CN)+2NaOH + Br ̧ = 2K ̧Co(CN); + 2KOH + 2NaBr.

REACTIONS OF GROUP IIIc.

In this group the phosphates and hydrates are dissolved in HCl and the excess of acid is neutralised with Na2CO3, then a solution of NaC2H2O2 and CH COOH is added. Al, Cr, and Fe are precipitated as phosphates.

If there is excess of H3PO4 in solution, or none of the above bases are present, then Fe,Cl, is added, drop by drop, as long as a precipitate falls; when a yellow colour appears, ferric acetate is being formed, in which ferric phosphate is soluble, therefore care must be taken only to add sufficient FeCl to precipitate the H,PO, in solution. All the phosphoric acid being removed, chlorides of Groups III. and IV. only remain, and are treated as in the General Table.

4

REACTIONS OF GROUP IV.

In this group the carbonates of Ba, Sr and Ca are decomposed with HCl, and the solution is divided into two portions:

1st portion-CaSO4 solution is added to test for presence of Ba.

BaCl2 + CaSO, BaSO4 + CaCl2.

2nd portion.-NH,OH is added to neutralise excess of HCl, and then CH COOH in excess is added to convert to acetates.

From the solution of acetates, K,Cr2O, throws down BaCrO4.

2

2Ba(C2H2O2)2 + K2Cr2O, + H2O = 2BaCrO4 + 2KC,H2O2+2CH3COOH. Sr is then thrown down by the addition of K2SO4.

Sr(C2H2O2)2 + K2SO4 = SrSO4 + 2KC2H2O1⁄2·

To the remaining solution an excess of NH,OH is added and (NH1)2C2O1, when the Ca is precipitated as oxalate.

Ca(C2H2O2)2 + (NH4)2C2O1 = CaC2O1 + 2(NH1)C2H ̧O2

THE SPECTROSCOPE FOR QUALITATIVE ANALYSIS

51

PART II.

CHAPTER I.

THE SPECTROSCOPE FOR QUALITATIVE ANALYSIS.

FIG. 35 gives the student an idea of the spectroscope and of its different parts.

P is a flint glass prism, having a refracting angle of 60° and resting on a brass plate fixed on a brass support, S. The brass plate carries the collimator tube C, in the end of which nearest to the prism is fixed a lens, the other end being closed by a plate in which there is a vertical slit, which can be widened or narrowed as required by means of a small screw

T

S

FIG. 35.

The tube E has also on the end nearest the prism a lens, and at the other end a reduced photographic millimetre scale which can be seen through the telescope T. At the end of E is placed an ordinary gas burner, a little distance from the photographic scale. Right opposite the slit in the collimator tube C is placed an ordinary bunsen flame, in which the substance to be tested is placed in the loop of a platinum wire. E is adjusted so that the image of the illuminated scale can be seen through

the telescope T, and the divisions are focussed by means of a small screw on E. All extraneous rays of light are shut off by covering up the apparatus with a black cloth or experimenting in a dark room.

Fig. 36 gives the spectra of the alkalis and alkaline earths, and with

care

seen.

The chlorides of these metals are used for the analysis, but in the case of potassium the solid KNO, is recommended to be used in the Pt. loop, as this brings out the violet line more distinctly.

The student should take all these salts in the order given, and in his note-book draw to scale each spectrum, only putting in the lines observed, then compare them with the chart.

TESTS FOR SOME OF THE RARER METALS.

Thallium. Soluble in HNO. TO is very soluble in H2O. HƠI (conc.) precipitates TICI (ous), white p'p't, from aqueous solutions, slightly soluble in HO, insoluble in NH,OH, but soluble in H2SO.

HS gives no p'p't from mineral acid solutions, but from an acetic acid solution a brown p'p't of TlS is thrown down. (NH4)2S also p'p'tes TlS. PtCl, p'p'tes from solutions of thallous salts, a yellow p'p't of Tl,PtCi. Tungsten. Insoluble in HCl or HSO4, slowly soluble in HNO3 or aqua regia. Mineral generally fused with Na,CO, and NaNO, when tungstates of the alkalis are formed which are soluble in HO. HCl in excess in an aqueous solution cold, gives a white p'p't of

H WOH2O; hot, a yellow p'p't of H2WO.

HS gives no p'p't in acid solutions, but turns the solution a blue colour. A solution of a tungstate with Zn, Sn, or SnCl2, and an excess of HCI, gives a characteristic blue colour.

Gold and Platinum are insoluble in HCl, HNO3, or H2SO, but soluble in aqua regia, yielding chlorides AuCl, and PtCl.

HS gives black p'p'tes of AuS and PtS, from chloride solutions in the cold, insoluble in HCl or HNO, but soluble in aqua regia and (NH4)2S. (PtS is only partially dissolved in (NH4)2S in the presence of other sulphides.) In boiling solutions metallic Au is p'p'ted and not AuS. From the (NH),S solution, AuS and PtS, are p'p'ted by the addition of HCl. FeSO gives a brownish p'p't of metallic Au with AuCl solution. AuCl solution is weak, a bluish coloration only is seen. Pt is p'p'ted by FeSO, only after boiling for some time.

If

SnCl, gives a purple p'p't (purple of cassius) in dilute solutions of AuCl,.

NHC with AuCl, and PtCl forms chloroaurates and chloroplatinates (NH,AuCl, and (NH),PtCl).

CH2O4 p'p'tes Au but not Pt from chloride solutions.

To solution of AuCl + PtCl add CH2O4

P'p't = Au. Solution. Evaporate down with NH4Cl = yellow p'pt (NH4) PtCl

Rhodium.-Alloyed with other metals Rh is soluble in aqua regia. H2S. From a hot solution of its salts, p'p'tes a sulphide insoluble in alkali sulphides.

Fused with KHSO1, and the fused mass treated with H2O, a pink Fused with KOH and KNO, gives RhO, insoluble in

solution is obtained.

acids and alkalis.

Melted with Zn and the alloy boiled with an acid, Rh is left as a black powder.

Palladium. Slowly soluble in HCl or HSO,; dissolves in the cold in HNO, forming Pd (NO3)2. Soluble in aqua regia, forming PdC14.

HS p'p'tes it as PdS, insoluble in (NH4)2S. PdCl is very unstable,