ELEMENTS OF QUALITATIVE CHEMICAL ANALYSIS. Camirftrge: FEINTED BY C. J. CLAY, M.A. AT THE UNIVERSITY PRESS. ELEMENTS OF QUALITATIVE CHEMICAL ANALYSIS. BY . H. SPENCEE, B.A. FELLOW OF THE CAMBKIDGE PHILOSOPHICAL SOCIETY. ULonUon anti = -ic salt, e. g. Feme Chloride Fe CL. to the greatest number of equivalents of acid radical j 13 BEHAVIOUR OF BASIC RADICALS WITH REAGENTS IN THE DRY WAY. N.B. The Blowpipe is to be used in all the following experiments, unless the contrary is stated. GROUP I. SILVER Nitrate of Silver. LEAD Acetate of Lead. MERCURY Mercurous Salts Subnitrate of Mercury. Mercuric Salts Chloride of Mercury. Heated on Charcoal. i. In the outer flame. In the inner flame with Na 2 C0 3 . non-volatile. Dark-red incrustation 1 . White metallic globules 5 malleable. non-volatile. Coloured incrustation. Orange (hot). Yellow (cold). Metallic globules. malleable 1 . With yellow incrustation 2 - volatile, Dense white incrustation. Fused with Carbonate of Sodium. In a glass bulb-tube, or tube closed at one end. Grey sublimate, on cool part of the tube 1 . 1 This does not occur with all ar- gentic salts. 2 The best way_ to render reduced metallic grains visible, as well as to test their malleability, in all cases, is to scrape off the reduced mass from the charcoal, arJ. wash it by tritu- rating in a small mortar with dis- tilled water, when the metal becomes distinctly visible. 1 The metal may be easily reduced without the aid of carbonate of sodium. 2 This incrustation is produced. because metallic lead is volatile at a red heat, and the oxide itself at a still higher temperature. The outer flame in this experi- ment acquires a blue colour, distin- guishing between lead and bismuth. i The salt is decomposed, the me- tal volatilizes and condenses upon the cooler neck of the tribe. 2HgCl + Na 2 C0 3 = Hg 2 CO 3 + 2NaCl and Hg 2 CDs = 2Hg. + CO 2 + O volatile The mercury salt must be anhydrous, and therefore should be dried, and the carbonate of sodium ignited, before use: with certain salts how- ever (chlorides) which are volatile without decomposition, the mixture must be moistened with water, and then expelled by gentle heat, before applying the blowpipe flame. 22 14 ^1 8 so SECTION i. ARSENIC. Araenioua Acid. O TIN. Stannous Salts rotochloride of Tin. Stannic Salts Bichloride of Tin. ta '& J=t o ^ & 00 1 9 ^3 != 0> S 1 2 S T3 S o. i 3V o i a ft s l M o> 2 1 ?li m " JSa Volatile. White incrustation. (distant.) Odour of garlic. Vhite crystalline subli- mate 1 in cool part of tube. Garlic odour. Mostly volatilize un- changed 2 . Black deposit if the substance is uncom- bined Arsenic). Yellow deposit (if a Sulphide). led crystalline deposit (if an Iodide). si -2 g-g i The crystals are minute octa- edra. 2 The current of air being ex- uded when the metal volati- zes, oxidation cannot take lace, hence the results in this tperiment (a) depend on the sub- ;ance with which the metal is jmbined. . K" O HH A 3a&a5aJ5 A , il 4 rt . 03 -2 3 O o >> oS O nj CQ i^a +3 -n r* " * t e .1 1 ol ll 1 If ^^ rt -iT| 'S'oj u < O-i lyS ^3 "S o-g >p fl.2 .5,5 13*3 " QtB "* 8'J3^ ^^ ^"~* "~fe* ^* CO "Q ^ S2 . 1 43 4s o ^i S le s 1 i B S |6 !ii!f - *> il -|S 03 "-> *> o-j .1-1 ^"S 00 S f4 I o a 03 & S i Metallic globules. malleable 1 . Salts of tin for the most rt, especially stannous chlo- e, are reduced without the aid fluxes. This should be tried, success denotes proficiency in s use of the blow-pipe. Che globules, dissolved in hy- jchloric acid and treated with ircuric chloride, give a white t. (See Group II. Sect. i. Tin.iv.) PQ P ~ ftfloSS -SSft a % 8 | | ^ 1 . 3 I ej a d d <* " W w | ^i | i J |1 B s |f|j ''ta^-S W "* acr 1 . d lH F- P ^^ -111 15 GKOUP II. SECTION n. BISMUTH. Subnitrate of Bismuth. CADMIUM. Chloride of Cadmium. COPPER. Sulphate of Copper. Heated on Charcoal. i. In the outer flame. ii. In the inner flame. Fuse to a Brown mass. On cooling becomes Yellow. Metallic globules 1 , brittle. With yellow incrustation. Red-brown incrustation 1 Metallic particles 1 . maskable. Heated on Platinum Wire with Borax. i. In the outer flame. Coloured bead 2 . Yellow (hot). Colourless (cold). Transparent clear bead. If saturated with Cadmium salt, becomes milk-white on cooling. ii. In the inner flame. Coloured bead. Green (hot). Blue (cold). Colourless (hot). Brick-red 8 (cold). 1 The reduction of metal is facili- tated by the use of carbonate of sodium. The incrustation is also more ap- parent when this flux is employed, since metallic bismuth is more vola- tile than the oxide. 2 Very small quantities of bismu- thic salt should be used, as other- wise the bead becomes opaque. Generally in all experiments with Borax on Platinum Wire, very small quantities of the salts to be tested should be employed, unless otherwise recommended. 1 The metal is reduced, volatilizes, re-oxidises as it passes through the outer flame, and condenses on a cool part of the charcoal as red-brown oxide. 1 The reduction of metal is facili- tated by the use of carbonate of sodium. The colour (copper-colour) of the particles is characteristic. If washed in a mortar, the colour and malle- ability become very apparent. 2 It is necessary here that the bead should be fully saturated with the salt of copper. 1C. GROUP III. ALUMINIUM. Sulphate of Aluminium. CHROMIUM. Sesquichloride of Chromium. IRON. Ferrous Salts Protosulphate of Iron. Ferric Salts Perchloride of Iron. Heated on Charcoal. i. In the outer flame, a. Alone. Residue moistened with CoN0 3 . Infusible. Incandescent mass, Blue coloration 5 ii. In the inner flame. Infusible. Green residue 1 Infusible. Colouredresidut Brown (hot). Red (cold). Infusible. Black'residue. Heated on Platinum Wire with Borax. i. In the outer flame. Colourless bead. Green bead. ii. In the inner flame. Green bead. Coloured bead 1 . Red (hot). Yellow, ] or j- (cold). Colourless ) Slightly Yellow (hot). Bottle-green, Colourless (cold). 1 Intense heat must be applied to produce this coloration, which is ex- tremely characteristic. i Both chromous and chromic salts behave in this manner. The chro- mous having this tendency to pass into a higher state of oxidation, are powerful reducing agents. 1 The variations in colour depenc on the quantity of iron salt present. 17 GEOUP IV. MANGANESE. Sulphate of Manganese. ZINC. Sulphate of Zinc. COBALT. Nitrate of Cobalt. NICKEL. Sulphate of Nickel. leated on Char- coal. In the outer flame, o. Alone. Infusible. Brown re- sidue. Infusible. Incande- scent residue 1 . Yellow (hot). . White (cold). Infusible. Dark-green powder. Infusible. Greenish or Dull-black residue. Residue moistened with CoN0 3 . Green coloration. In the inner flame. White incrustation 2 (distant.) used on Plati- um Wire with Borax. In the outer flame. Coloured bead. Amethyst. Clear bead 3 . Coloured bead 1 . Blue. Coloured bead. Violet (hot). Red-brown (cold). In the inner flame. Colourless 1 , Milk-white 4 . Blue. Grey 1 . used on Plati- nm Foil with ra,CCX + KNO, Bluish-green colora- tion (cold). 1 Care must be taken to use an extremely minute quantity of manganese salt. The bead assumes a pink co- lour before becoming colour- less. 1 The brilliant incandescence is characteristic. The colora- tion only appears on removal from the flame. 2 As has been pointed out in analogous cases, reduction of metal first takes place, the metal volatilizing, oxidising, and condensing on a cool part of the charcoal support, s If saturated with the zinc salt. * Intense heat should be a- voided, or reduction of metal takesplace, and the metal alloys with the platinum. 1 By the colour of this bead, cobalt may be recognized even in the presence of other metals. 1 On adding nitrate of po- tassium to this bead, and heat- ing again inthe oxidising flame, it assumes a purple tint. V 18 GKOUP V. BARIUM. Nitrate of Barium. STRONTIUM. Nitrate of Strontium. CALCIUM. Chloride of Calcium. MAONESIU Sulphate of Magnes Heated on Char- coal. In the outer flame, a. Alone. Infusible residue 1 . Slightly incandescent. Infusible residue \ Slightly incandescent. Infusible residue '. Highly incandescent 2 . Infusible residi Highly incandes jS. Residue moistened with CoN0 3 . Pale pink coloral Heated alone on Platinum Wire. Flame is coloured 2 . Yellowish-green. Flame is coloured 2 . Crimson. Flame is coloured. Orange-red 3 . i Chlorides, bromides, and iodides of barium resist de- composition into the oxide, and hence remain as a fused mass upon the charcoal. 2 An alcoholic solution of a barium salt manifests this re- action equally well. 1 Chlorides, bromides, and iodides of strontium behave like the corresponding salts of barium. 2 An alcoholic solution burns with a crimson flame. The colour is perceptible in presence of a barium salt. 1 Chlorides, bromides, and iodides remain undecomposed. 2 The incandescence is ob- served both in the case of the oxide or undecomposed chlo- ride, bromide, and iodide. 3 Pure calcium gives a red flame, the orange tint being due to a trace of sodium. The flames of strontium and calcium should be care- fully compared, as some con- fusion is liable to occur in determining between the co- lours of these flames. Calcium cannot be detected by the coloration of its flame, in presence of strontium. 1 If water is present, t ride, bromide, and io< magnesium decompose thus: 2 Mg Cl + HzO =Mg 2 O + 2 In presence of oth tallic oxides this cole does not occur. 19 POTASSIUM. Nitrate of Potassium. GROUP VI. SODIUM. Sulphate of Sodium. AMMONIUM. Chloride of Ammonium. LITHIUM. Chloride of Lithium. Volatile. leated on Char- Fuse into the char- Fuse into the char- White incrustation. Fuse into the char- coal. coal. coal. coal. In the outer flame. leated on Plati- Flame is coloured 1 . Flame is coloured 1 . Flame is coloured. num Wire. Violet. Yellow. Carmine 1 . i Part of the salt volatilizes (since certain salts of potas- i Sodium salts are more vola- tile at an intense red heat than i The colour of this flame re- sembles that of strontium, but sium, especially the chloride and nitrate, volatilize at an intense red heat) and is decom- the corresponding potassium salts, hence the coloration of the sodium flame is more differs from it in containing less yellow. Presence of salts of sodium posed by the carbonaceous con- stituents of the flame. Potas- marked. obscures this reaction. Potas- sium does not materially inter- sium is set free in the form of fere. vapour and burns with the characteristic violet flame. The coloration is not per- ceptible to the naked eye in presence of sodium. The in- terposition of a piece of dark blue glass between the eye and the flame renders it perfectly visible, since the blue glass in- tercepts the yellow rays of the sodium flame. 3 20 THE PROCESS OF SOLUTION. (1) All bodies must be reduced to the liquid state (if not already in that condition) before the experiments in the following tables can be performed. (2) The following solvents are usually employed in analysis, and are applied suc- cessively in the order here given : Water. Hydrochloric Acid. Nitric Acid. Nitro- hydrochloric Acid. (3) The substance must be reduced to a fine powder in a mortar, before proceeding to dissolve it, in order to facilitate the action of solvents. (4) The solubility or otherwise of any solid in a solvent may be ascertained by boiling the solid in the liquid, allowing the undissolved residue (if any) to subside, decanting the supernatant liquid, and evaporating a portion of the latter on platinum foil. If a residue remains on the foil, the solid may be deemed sufficiently soluble for all ordinary purposes. (5) Decantation should always be preferred to filtration, in the process of solution, if possible. (6) Before treating any substance with acids, the student should endeavour to deter- mine the particular acid which is likely to be applicable to any given salt, as an inference from the preliminary examination with the blowpipe, or by a reference to the tables of reaction. e. g. If Silver, Lead, or Mercury, have been detected by the blowpipe experiments, and water fails to dissolve the salt operated upon, Nitric Acid must be employed as the solvent (Gr. I. col. i). 21 (7) The above acids should be employed in a tolerably concentrated form and iu small quantity. Any required amount of dilution can readily be obtained after boiling with the strong acid. Some bodies dissolve in dilute acids which will not dissolve in strong acids, whilst other bodies dissolve in the latter and are reprecipitated on dilution. In the latter case the substance must be treated as directed in the following paragraph. (8) If a body resists solution in water, hydrochloric acid, nitric acid, and nitro- hydrochloric acid, it must be well mixed with four or five times its weight of dry carbonate of potassium and sodium, fused in a porcelain crucible (over a gas burner or in a furnace) and allowed to cool. The fused mass must then be treated, with water, and heated. If water fails to dissolve it, the acids mentioned in (2) must be employed, but in, all cases the mass must be well washed with water in order to remove any soluble bodies which may be present. (9) In the case of compounds of cyanogen, in order to guard against possible contingencies, the substance should be decomposed by boiling with solution of hydrate of potassium, and some carbonate of sodium ; the residue washed and dissolved in acid. 32 22 CQ S5 PH O d & o J' o of f^ M 'g H 1 M B 1 P^ S > 1 s 3 'a "B .1-1 M J3 5 o 02 | O ^ a J o ra > o " ^ . "3 ^_ra IH 2.1 tO 'o? _^ ^ sS S T3 to i j >.? C3 j .rH i. S q,l s a 9 ' VJ GO to a a 1 -o w ^S S J.g- K) o g w 1 ~~r '3 '3 ^j 5- rC ' rt 3 W .-s to 2 * cS O 3 II 1 ^ fi f |a a o S || o II t3 o i, &C 00 "CJ II * S 1 of >* 1 w pi --3 PR 8 ? 1 . M .J ^H S " 1^1 T S Q s 1 a) H CO T3 T3 w" . * ?* ^ a fl .2 c ^ O ^ "o-- pM 53 ^ M + f I ! ? S3 o 1 O fl M M ^ 8- ^ T M H S li'/i ^i -3 -^ j3*1l1 w .g.g w 1 v* --H CQ " ?; os ^3 n PO |||ll K? qj 'm 3 1 02 ' ^ ol o 02 PH l PH * "g - *H PH O c,., M ^ 3 o ^1 ^ i a 1 HH . *4-l S < 0> O /-i LUTIONS OF THI LEAD Nitrate of Leac II 1 In 2 n Q 60.3 M a^ J bNO 3 + H 2 S black sol. in alkaline sulphid 1. in boiling nitric acid bN0 3 + 4 NH 4 HO = white7 sol. in excess of hydrat 1. in excess of hydrate t)NO 3 +KHO = white 1. in excess of hydrate < on heating. )NO 3 + KCr0 2 yellow 1. in hydrate of potass: sol. in water and nitric N O 02 PH i g " j a OH S s g s .g 1 ^ 1 to a 3 a 1 PI H > O | 1 O ^ O H^ W

> II ^, l> 'S U 00 . ^ ^5 rM "1 w M AgN0 3 + HCl White (curdy) c insol. in water. , sol. in hydrate of nitric acid. 2 AgN0 3 + H 2 S black j8 insol. in alkaline of ammonium sol. in conc d . nitri< AgN0 3 + NH 4 HO olive-greenT- add HCI as soow sol. in excess of hy 2AgN0 3 + 2KHO brown insol. in excess of IM o O .S S "M" 3 '? ^"s" S '1 | g 7 |J| O a ' 02 "1 o 3 t,' O <" aa'g W S'"T g" S-S 40 _=f ^ o ^ r2~'s bo 03 w <*-, to Sft^, "* fc.al-al-s 1 , !l ^ II KP^ 10 ^Jl O I H 15 : ' s > , -s '38 a^ s i'o'S- 2 ^'^ ^ I * "11 'I "Q)" .J^ S = -^ il 5 l3W?8t5s|lf!: 3gg 3. .2 d g^_ 5-9O + fc ,*sii! c o"j3 s~ a S3 12 t> '*' 3 ti ^ o S.sS'SW -M^-S^-SQ'^'S'") Sg Hg 2 N0 3 + KI green-yellov sol. in excess < B" I 1 -3 1 + r&'jj ^ .-? o> ~S o _r O ^-3 ^J3 ^ ^- -f-i zP O t"H o O ^i 05 to 3 -t- 3 O "w + o CO P< O ,2 (7 ^ % >> bo o> w & ii -I1|i SwJ o. 7-e "o v TJ Cj O W 15 M ii! 1* 11|!i a O O 'i i 3^ .3 - *,* J ^-9 "3^12-g "S B o J * o "ft2 ^-^"^o .Sa '^s^^d)-*^ 11 O ^2 ^ PI'S ft'cS.'SD'S ^"o ^^uS 10 ^*- 02 2 tTo M^ B R ^O n """'M -Q 01 ^ 4-3 ^2 (U S B -3 M " M 'S ' d ,a iSa'a*?^" ^ *H An -g g ^.2 ^.a S^S'fi B "Ss-sS^El ^5 bo^ . "Q a .b c8t g>- 2j-. JeiBoac38 ""i "^ .S ? to ^ a "^ ^*^ o c^"^ 5^?^^^.^ ii ^3 * ^ ^ 'ert^S ^'c3 C ^^ .rH^O f^ ^^Q II 3 " If 2 ^^"SS Ss M ""o B *1Sj rt . % .al s g)^ 00 -^ S'^ 3 '"c'.-'S' &Q * isx? 8 ," 1 " "

a)'=5 4) g - s2 -2 2"o "" PH IM O TH j O 3 fl + 2 i-s! || |gp I |f|J . ''fet) CD tS U ! bo-^ Jo *^ "* "S^fO O _j. g'~ ^fS w .3 > _s 'o.S'" - fl^ S^* 3 ' M -> r a'S'Sfc' 2 jg to pJ^OT ^! ^rS 1 ^ M^ 'S'^'^QS-O g Q) S . s 03 -sF'll i| if *Ifsl o II to II 'aT c3 PH II -w"* 3 ^5 c"-2 a 5 8 J? rt * M "S e "-S rt *> o 3 tfi nT M S fll^ll.g 1 1 |l (g^^iillif H 1 ^ If II "3) 5 a Ilii Pl^f ft! ill fe rt _; rt - ^ + M o t^ dT*^ ?3 ^ ^* '^'S'S^^ r ^r-*oS^S C S |*|tl O" S3 S .3 ^5 .S ^ o".S ^ S bo 3 |l|P||||l!| ^ 1 1 1 2 S] it only dissolves completely when a higher sul- phide is used (NH 4 )2S2. /S Hydrochloric acid reprecipitates as stannic sulphide (Sn 2 S2>. y Part of the tin becomes oxidised at the expense of the other part thus : 4 SnHO + 2KHO=K 2 Sn 2 O 3 + 3H 2 + Sn 2 . 8 Stannous chloride removes all the chlo- rine from the mercury, and metallic mercury separates as a grey deposit. Hence the value of stannous chloride as a reducing agent. a Alkaline solutions are not precipitated. If the stannous chloride is in excess the ppt. is white. j3 The salts of stannic acid have the general formula M 2 S 2 C>3. Another modificaton of the hydrate ex- ists, as Metastannic acid, having the formula HioSnioOjs. It is produced by the action of concentrated nitric acid upon metallic Tin, as a white powder. Its salts have the general formula M 2 HsSnioOi5. o This ppt. only forms completely in acid solution. ft SbgOa should be dissolved in hydrochlo acid, evaporated to a small bulk, and th poured into much water, when the white o: chloride will be precipitated*. y This reaction distinguishes antimonk oxychloride from bismuthic oxychloride (i Bismuth, Gr. IL Sect. n.). * This ppt. will often appear on simply luting solutions of antimonious salts, may then be removed by hydrochloric acid. 25 CTION I. EIR SALTS, AS SULPHIDES, BY HYDROSULPHURIC ACID. LPHIDE OF AMMONIUM. JTIMONY (Antimonic salts). ARSENIC (Arsenious salts). ARSENIC (Arsenic salts). Antimoniate of Potassium. Arsenious Acid. Arsenic Acid. 8 Sb0 3 a+ 5 H 2 S = ange-yellowiS Sb 2 s 6 in sulphide of ammonium, reppt. by hydrochloric acid, in hydrate of potassium 7. orange^, As 2 s 3 sol. in sulphide of ammonium, reppt. by hydrochloric acid, sol. in hydrate of potassium. sol. in carbonate of ammonium. yellow a As 2 s 5 sol. in sulphide of ammonium, sol. in hydrate of potassium, sol. in carbonate of ammonium. I. Sulphides. II. Hydrates and Oxide. hite H 3 Sb0 4 metantimonic acid 8. in hydrate of ammonium, in water, reppt. by acids. 2H 3 As0 6NH 4 HO green ......................... 2Cu 3 As0 3 e sol. in hydrate of ammonium and acids. 6NH 4 HO bluish-green 2Cu 3 As0 4 sol. in hydrate of ammonium. III. Hydrate and Oxychloride. IV. Mercurous Chloride. V. Cupric Arsenites and Arseniates. H 3 As0 3 ) + [+ 3 AgN0 8 = 3 NH 4 HOJ yellow Ag 3 As0 3 sol. in hydrate of ammonium, nitric acid, and acetic acid. H 3 As0 4 + 3 AgN0 3 = brick-red? Ag 3 As0 4 sol. in hydrate of ammonium, nitric acid and acetic acid. VI. Argentic Arsenites and Arseniatee. f the acid metantimoniate of potassium, ranular antimoniate (such as is employed esting for sodium) is used, the formula L2SbaO 7 must be substituted for the above. Presence of tartaric acid prevents pre- ation. Lntimoniate of potassium separates on ding, as a crystalline ppt. trictly the above reaction consists of two 3, an oxychloride of antimony being first led thus : SbCl 5 + H 2 O = Cl 3 SbO + 2HC1 and ClaSbO + 3H 2 O = H 3 SbO 4 + 3HC1. intimonic acid is very unstable, rapidly ing into antimonic acid. H 3 SbO 4 -H 2 O = HSbOa. ce in many works the product of the Te- rn of penta-chloride of antimony with ;r, is called antimonic acid, lere are three modifications of antimonic ate riimonte Acid (HSbOs) formed from illic antimony and aqua regia. etantimonic Acid (HaSbC^) formed as wantimonic Acid (H^SbaOy) formed by de- posing an alkaline antimoniate by an acid, is the metantimonic acid of Fremy and r chemists, forms two classes of salts b 2 O 7 and M 2 H 2 Sb2O 7 . It is analogous s properties to metantimonic acid, lis series is analogous to the phosphoric is. (See Odling's Manual, p. 3S6.) a Arsenious acid is only known in the state of aqueous solutions. It may be prepared by boiling arsenious anhydride (white arsenic) in water, on cooling a portion of the latter is held in solution. /3 Alkaline solutions are not precipitated : the above ppt. only occurs in presence of a free acid, such as hydrochloric acid. y The oxide is obtained when ores of metals containing arsenic are roasted. It occurs in two varieties, the vitreous and crystalline. fi The aqueous solution of arsenious acid used in this and the following experiment, must be exactly neutralised by hydrate of ammonium, otherwise no effect is produced. Known as Scheele's green. o The ppt. does not form immediately, even in a concentrated acidified solution : prolonged passage of hydrosulphuric acid is required to throw down the sulphide. The ppt. is most completely formed by boiling arsenic acid solution with sulphurous acid until no odour is evolved, thus producing arsenious acid (H 3 As04 + HgSOs = H 3 AsOa + H 2 SO4), then passing hydrosulphuric acid gas. The sulphide as above seems to be merely a mixture of one atom of tersulphide (AszSs) and two atoms of sulphur. /3 The oxide is obtained by oxidising arse- nious anhydride (As 2 O 3 ) or arsenious acid (HsAsOs) by means of nitric acid. It oc- curs in the form of long prisms, containing 2H 3 AsO 4 + H 2 O. v The ppt. is more completely formed when the solution of arsenic acid is neutralised by hydrate of ammonium. 26 GEOUP II. SECTION i. (Continued.) METALS WHICH ARE PEECIPITATED FROM SOLUTIONS OF THEIR SALTS, AS SULPHIDES, BY HYDROSULPHURIC ACID. THE PRECIPITATE SOLUBLE IN SULPHIDE OF AMMONIUM. PLATINUM. Bichloride of Platinum. GOLD. Terchloride of Gold. Hydrosul- phuric Acid. brown-black Pt 2 s 2 sol. in sulphide of ammonium, reppt. hydrochloric acid. black Au 2 s 3 sol. in sulphide of ammonium, reppt by hy- drochloric acid, sol. in hydrate of potassium. I. Sulphides. II. Hydrate of Potassium. yellow (see iv) KPtCl 3 The formula of the hydrate, produced by the action of hydrate of potassium not in excess on auric chloride, is not known a. II. Chloro- Platinate III. Iodide of Potassium. PtCl browii7 Ptl 2 sol. in alcohol, forming a yellowish-green solution. AuCl 3 green/3 Aui 3 ill. Iodides. Chloride of Potassium. PtCl 2 yellows. insol. in alcohol. .KPtCl, IV Chloro- Platinate. V. Ferrous Sulphate. AuCl 3 + 3 Fe 2 S0 47 brown powders (Fe 2 ) 2 (S0 4 ) 3 + Fe 2 Cl 3 Au v. Reduction of Metal. VI. Stannous Chloride. The addition of stannous chloride to a solu- tion of platinic -chloride, containing ex- cess of hydrochloric acid, gives a brown solution e. purple AuSn 3 3 ? Purple of Cassius e. VI. Purple of Cassius. a The ppt. does not usually form immediately, heat promotes its formation. In an alkaline solution the precipitation is only partial. /3 The hydrate is only produced when hydrates of the alkalies are added to a solution of platinic nitrate. y The ppt. only forms upon standing or heating. The solution is coloured immediately. S In dilute solutions the liquid, after adding chloride of potassium, must be evaporated to dryness, and the residue treated with alcohoL e The coloration is due to the reduction of platinic chloride to the condition of platinous chloride (PtCl). a If hydrate of potassium in excess is added to a solution of auric chloride no ppt. is produced, but on adding tannic acid to the clear solution, a black ppt. is formed (Au 2 O). /3 The ppt. dissolves on agitation. y Excess of hydrochloric acid must be present, otherwise an insoluble salt of iron would be formed. S By means of ferrous sulphate, gold may be detected in extremely dilute solutions by the violet or blue tint which is imparted to them on addition of this reagent. If the above ppt. is dried, it exhibits metallic lustre when rubbed. e When the quantity of gold present is very minute, a dusky red tinge pervades the solution. The reaction is more delicate if stannous chloride contains some stannic chloride. The best way of applying the test is as follows. The solution to be tested should be placed with much water in a beaker and acidified with a few drops of nitric acid or ferric chloride. The stannous chloride, containing a trace of stannic chloride and acidified with hydrochloric acid until quite clear, should then be poured slowly into the solution to be tested, when the characteristic colour will mark the course of the precipitant through the solution. In actual analysis, a special and separate examination of a portion of the original solution is made, when the presence of one or both of the above metals is suspected. SPECIAL TESTS FOR ARSENIC. I. MARSH'S TEST. BEHAVIOUK OF ANTIMONY AND ARSENIC BY THIS METHOD, CONTRASTED. Experiment. Hydrogen gas is generated from zinc and sulphuric acid (both previously proved to be perfectly free from arsenic). The solution to be tested is introduced into the generating apparatus. The gas (SbH 3 or AsH 3 ) is dried. A fine jet of hard glass is attached to the apparatus, at the end of the drying tube, and the escaping gas (SbH 3 or As H 3 ) is ignited (after allowing all the air to be displaced). A cold porcelain surface is depressed into the name. The metallic spot is treated with nitric Iacid, which is carefully evaporated, and then nitrate of silver is added. The metallic spot is treated with solu- tion of hypochlorite of sodium a. The spot is moistened with solution of sulphide of ammonium. That portion of the jet-tube nearest the CaCl, is heated by the blowpipe flame. The tube containing the mirror is de- tached from the hydrogen apparatus and attached to one in which pure H 2 S is being generated (washed and dried by passing through H 2 S0 4 ) ; gentle heat is at the same time applied to the mirror. The tube with the altered mirror is attached to an apparatus from which HC1 is evolved (by heating a concen- trated solution and drying by means of H 2 SO,). The volatile SbCl 3 is conducted into water, which dissolves it. H 2 S is passed through this solution. Antimony. Result. Arsenic. Sb unites with nascent hydrogen form- ing Antimoniuretted Hydrogen. SbCl 3 + 6H = 3 HCl + Sbff a . By passing through sulphuric acid, or over chloride of calcium. Burns with a bluish-green jtame; white fumes arise = Sb 2 O 3 . A black spot of metallic antimony ap- pears, which is lustrous if thin a. No change of colour occurs. The spot scarcely at all dissolves j8. The spot immediately dissolves. A lustrout mirror appears on the inside of the tube beyond where the blowpipe name impinges -y. The mirror becomes of a reddish-yellow or brownish-black colour 5. The Sb 2 S s entirely disappears e. Orange ppt. of Sb 2 S 3 . As unites with nascent hydrogen, form- ing Arseniuretted Hydrogen. As 2 3 + 1 2H = 3H 2 + 2 AsH 3 . By passing over chloride of calcium. (Sulphuric acid decomposes AsH 3 .) Burns with a bluish-white flame; whi.'e fumes arise =As g O 3 ; garlic odour. A black lustrous spot of metallic arsenic- appears a. Colour changes to yellow or red. If oxidation has given rise to arsenious acid, it will change to yellow; if to ar- senic acid, it will change to red. (See Table for Group II. Sect. I.) The spot immediately dissolves. The spot remains undissolved. A lustrous mirror appears on the inside of the tube, at some distance beyond where the blowpipe flame impinges/3. The mirror becomes lemon-yellowy. No change occurs. o Really NaClO+NaCl, prepared by mixing a solution of CaCl and Na 2 CO 3 in excess, and fil- tering. a The cold surface reduces the temperature, hence a portion of the antimony or arsenic is not oxi- dised (as it is when burning, giving rise to white fumes), but condenses on the cold surface. ft Antimony cannot be detected by this means, in the presence of arsenic. y Heat decomposes SbHa into its constituents, and metallic Sb is deposited, the gas escaping at the jet being almost pure H. S This Ls due to the conversion of the metallic Sb into Sb 2 S 3 . e It is converted into volatile, colourless SbCla. a If the porcelain be allowed to remain in the flame more than a second or two, the spot disap- pears, from volatilization of the metal. ft As is more volatile than Sb, hence is deposited in a cooler part of the tube. y Due to formation of AsgSs. (See Table for Group II. Sect. L) This test will only serve to distinguish whether one or both of these metals are present in a sub- stance. It will not indicate one, with certainty, in the presence of the other. If arsenic alone is present it is decisive. 4 28 II. REINSCH'S TEST. Clean metallic copper when boiled with a solution, containing arsenic or its com- pounds, acidified with hydrochloric acid, reduces the arsenic to the metallic state. The latter forms a steel-grey film upon the copper, or if the quantity of arsenic is considerable and the boiling is prolonged, it appears as large black scales. The film or scales may be sublimed and so converted into arsenious acid, which appears as iridescent octahedra. This may be further tested by boiling in water and treating with hydrosulphuric and hydrochloric acid gas, or by nitrate of silver. METHOD OF APPLICATION OF KEINSCH'S TEST. Experiment. Result. The solution to be tested is boiled with ^-th its bulk of hydrochloric acid. Pieces of copper wire (an inch long) previously cleaned with concentrated nitric acid and washed, are boiled with the hydrochloric acid solution, for two or three minutes. The copper is removed, washed with distilled water, dried between bibulous paper, or in a water- bath, introduced into a hard glass tube contracted at one end, and heated by holding it obliquely in a gas flame. The portion of the tube containing the sublimate is filed off and boiled in water. A portion of the solution is tested by hydrosulphu- ric acid gas. Through the same solution hydrochloric acid gas is A second portion is tested with nitrate of silver, (taking care to neutralize first with ammonia). Arsenic, if present, is reduced on the surface of the copper, either appearing as a grey discoloration or film, or as large black scales. A crystalline sublimate of arsenious acid forms on the cool part of the tube. Solution of arsenious acid is formed. Yellow tersulphide of arsenic is precipitated. No change takes place. Yellow arsenite of silver is precipitated. 29 III. FRESENITJS' AND BABO'S TEST. If arsenites, arsenious acid, or tersulphide of arsenic (the latter is preferable when merely trying the reaction) are fused with equal parts of dry carbonate of sodium and cyanide of potassium, the whole of the arsenic is reduced to the metallic state. Being extremely volatile, it condenses again, if the operation is conducted in a bulb- tube, upon a cool part of the tube, forming the characteristic arsenical mirror. If the operation is conducted in an apparatus which ensures the preservation of the arsenical vapours from contact with the atmosphere, the delicacy of the test is so far increased as to render it at once the least objectionable in its application and the most efficacious as a means of detecting the presence of arsenic. Fresenius and Babo instituted a series of experiments which shewed that the required delicacy could be obtained by heating the mixture of the arsenical compound, carbonate of sodium and cyanide of potassium, in a stream of carbonic acid gas (anhydride). METHOD OF APPLICATION OF FRESENIUS' AND BABO'S TEST. Experiment. Result. Carbonic acid gas is generated in an ordinary gas apparatus, from lumps of limestone or marble and hydrochloric acid. The gas is dried by passing it through sulphuric acid. The mixture (3 parts dry carbonate of sodium, i part dry cyanide of potassium, i part dry tersul- phide arsenic, intimately mixed in a mortar) is intro- duced into a combustion-tube of hard glass, drawn out at one end and attached at the large end to the egress tube of the wash-bottle. The gas is allowed to pass so as to expel all air, and then at the rate of one bubble per second (this can be effected by pouring water into the generating bottle). The combustion tube is heated in its entire length, to expel all moisture, then to redness at the shoulder beyond the mixture, and then at the same time the mixture until it is entirely fused. The portion of the tube containing the mirror may be cut off with a file and after dissolving in water, may be further tested by means of nitrate of silver, as in the case of Reinsch's or Marsh's test. The vapours of metallic arsenic are carried on- wards by the carbonic acid gas, and the shoulder of the tube being heated, they pass on and condense in the drawn-out portion as a lustrous mirror a.. A garlic odour may be detected at the end of the tube. No compound of antimony whatever yields a similar reaction under the circumstances. a. If only a minute quantity of Arsenic is present, the mirror appears as a thin grey film. 4 2 30 GROUP II. METALS WHICH ARE PRECIPITATED FROM SOLUTIONS OF THE PRECIPITATE INSOLUBLE MERCURY (Mercuric salts). BISMUTH. Perchloride of Mercury. Terehloride of Bismuth. *Hydrosul- phuric Acid. 6HgCl + 2H 2 S Whitea 2(HgCl.Hg s S) insol. in sulphide of ammonium, insol. in nitric acid. brown-black Bi 2 s 3 insol. in sulphide of ammonium, sol. in nitric acid. II. Hydrates of the Alkalies. HgCl + KHO/3 reddish-brown? HgHO (if only a small quantity of KHO is added.) insol. in excess of hydrate of potassium ; on adding the excess, the ppt. is converted into the yellow oxide (Hg 2 O). insol. in hydrate of ammonium. 3 BiCl 3 + 6KHO White (flocculent) BiH 3 3 . Bi 2 O 3 insol. in excess of hydrate of potassium /J. insol. in hydrate of ammonium. Action of Water on Bismuthic Salts. III. Hydrate of Potassium. 4 HgCl+ 2 KHO yellows 2Hg 2 o insol. in excess of hydrate of potassium. 3 BiCl 3 + 3 H 2 white? BiCi 3 .Bi 2 o 3 insol. in tartaric acid (see Antimony, p. 24). IV. Iodide of Potassium. HgCl + KI scarlet Hgl sol. in excess of iodide of potassium. BiCl 3 + 3 KI brown (cystalline) BiI 3 insol. in excess of iodide of potassium. V. Chromate of Potassium. sol. in acids. yellow ............ Hg 2 . HgCr0 2 Stannous Chloride. Metallic Iron. 2HgCl+SnCl white ppt Hg 2 Cl + SnCl grey deposits ... = SuCl 2 + Hg 2 Cl ....Hg 2 Cl Hg VII. Cyanide of Potassium. Soluble + 3 KCr0 2 lemon-yellow Bi(CrO 2 ) 3 sol. in nitric acid and hydrate of ammonium, insol. in hydrate of potassium 8. BiCl 3 + 3 KCy white BiCy 3 insol. in excess of cyanide of potassium. \ a The white ppt. is only produced by small quanti- ties of the reagent. If the experiment is carefully per- formed, the colour will become, according to the amount of reagent added, yellow, orange, brown, and finally black from formation of the black sulphide (Hg 2 S). The white ppt. has the formula assigned to it. P The action of hydrate of ammonium on mercuric salts is to form a double chloride and amide of mer- cury (HgCl . HgNHs) thus : 2HgCr+2NH 4 HO=(HgCl . HgNH 2 )+NH 4 Cl+2H 2 O. Iheppt. is known by the name of " white precipitate." y The hydrate rapidly passes into the oxide (Hg 2 O). The experiment as detailed in II. must be carefully performed or the reactions will not occur. S When mercuric oxide is prepared in any other way than by the action of an alkali, it is red. e This reduction of metal takes place when mercuric chloride is boiled with excess of stannous chloride The deposit if boiled with hydrochloric acid takes the form of globules. f With mercuric nitrate, cyanide of potassium gives a white ppt. soluble in excess. o A solution of bismuthous nitrate in water and hydrochloric acid may be substituted for bismuthic chloride. /3 If after adding excess of hydrate of potassium, the ppt. is allowed to subside, the supernatant liquid de- canted, and the residue evaporated to dryness, the ppt. will be converted into Yellow Oxide (Bi 2 O 3 ). The yellow oxide is not formed on merely boiling the ppt. Y These salts are also termed basic salts. The chlor- ide is usually employed in this reaction, as its decom- position is most complete; with nitrate, a mixed hydrate and nitrate of bismuth results. 3Bi(NO 3 )3+6H 2 O=[Bi(NO 3 ) 3 . 2BiH 3 3 ]+6HNO 3 . 8 The solubility of bismuthic chromate in nitric acid and its insolubility in hydrate of potassium, dis tinguish it from plumbic chromate. 31 SECTION n. THEIE SALTS AS SULPHIDES BY HYDROSULPHURIC ACID. IN SULPHIDE OF AMMONIUM. CADMIUM. Chloride of Cadmium. COPPER. Sulphate of Copper. 2CdCl+H 2 S brilliant yellow-. Cd 2 s insol. in sulphide of ammonium. sol. in nitric acid. insol. in cyanide of potassium a. Cu 2 S0 4 +H 2 S black (in flakes) a Cu 2 S insol. in sulphide of ammonium. sol. in nitric acid. sol. in cyanide of potassium. I. Sulphides. CdCl+KHO/3 white CdHO insol. in excess of hydrate of potassium 7. sol. in hydrate of ammonium. cold blue (flocculent)7 ............ 2 CuHO insol. in excess of hydrate of potassium. boiling converts this ppt. into the black oxide .(Cu.O). sol, in hydrate of ammonium 5. II. Hydrates. soluble. boiling Cu 2 S0 4 + 2KHO = blacke Cu 2 o sol. in hydrochloric, nitric, or sulphuric acid, forming corresponding cupric salts. Cu 2 S0 4 + 2 KI = 1 + brown Cu 2 l sol. in excess of iodide of potassium. III. Oxides. IV. Iodides. CdCl + KCr0 2 yellow. .CdCrO, yellow-brown 2CuCrO s sol. in nitric acid and hydrate of ammonium, with the latter forming a green solution. V. Chromates. Cu 2 SO 4 + Fe s = Cu a + Fe 2 S0 4 metallic coating on the iron Cu presence of an acid (HC1) accelerates this action. VI. Reduction of Metal. CdCl + KCy white CdCy sol. in excess of cyanide of potassium. Cu 2 S0 4 green-yellow aCuCy sol. in excess of cyanide of potassium f. VII. Cyanides. a This reaction serves to distinguish between cad- mium and copper in the process of analysis. /3 Hydrate of ammonium also produces a white ppt. of hydrate with solutions of cadmium salts, but it is readily soluble in excess of the precipitant. y On treating this solution, as directed in note /3, Bis- muth, the Broim Oxide (CdaO) is formed. a This ppt. rapidly absorbs oxygen from the air and passes into cupnc sulphate : Cu 2 S+O 4 =Cu 2 SO 4 . /3 Cupric sulphate produces with hydrate of ammo- nium a green-blue ppt. of basic sulphate of cupram- monium [(NHaCuhSO-t]. See note 8. y If the precipitant is deficient in quantity a green basic salt is formed. 8 Cupric hydrate dissolves in hydrate of ammo- nium, forming a blue solution. The metal is supposed to replace 1 eq. of hydrogen in the molecule of ammo- nium (NHi), and so to constitute the basic radical termed " Cuprammonium" . e At a red heat cupric oxide gives up its oxygen to hydrogen or carbon hence its value m organic ana- lysis. f Hydrochloric acid precipitates white cuprous cyanide (Cu 2 Cy) from this solution, soluble in excess. 32 GROUP METALS WHICH AEE PRECIPITATED FROM SOLUTIONS OF ALUMINIUM. Chloride of Aluminium. CHROMIUM. Sulphate of Chromium or Chromic Acid. Hydrate of Ammonium. White (gelatinous) a A1 2 H 3 3 nsol. in excess of hydrate of ammonium. sol. in hydrate of potassium j3. nsol. in chloride of ammonium. (Cr 2 ) 2 (S0 4 ) 3 bluish-green Cr 2 H 3 o 3 .nsol. in excess of hydrate of ammonium, sol. in hydrate of potassium, nsol. in chloride of ammonium. II. Hydrate of Potassium. ALCl, + 3 KHO white- Ai 2 H 3 o 3 sol. in excess of hydrate of potassium, and reppt. by chloride of ammonium 7. not reppt. on boiling. ' (Cr 2 ) 2 (S0 4 ) 3 +6KHO = green 2Cr 2 H 3 o 3 sol. in excess of hydrate of potassium, and reppt. by chloride of ammonium. also reppt. on boiling. III. Sulphide of Ammonium. 2 A1 2 C1 3 + 3 (NH 4 ) 2 S = 6NH 4 C1 + (A1 2 ) 2 S 3 and (A1 2 ) S 3 +6H,0 white ppt. 5 2 A1 2 H 3 3 + 3 H 2 S. A similar reaction occurs with chromic salts and sulphide of ammonium as is the case with salts of aluminium. IV. Ferri-Cyanide of Potassium. v. Ferro- Cyanide of Potassium. The greenish ppt. usually produced by ferro- cyanide of potassium with solutions of aluminium salts, is a hydrate containing some cyanide of iron e. VI. Sulphate of Potassium. white . A1 2 K(S0 4 ) S : common alum TJ soluble a. VII. Silicate of Potassium. Al 2 Cl 3 + 3 KSi0 2 white.. Ai 2 (Si0 2 ) 3 ?. a The ppt. dries into a transparent horny, mass. /3 When the ppt. is dissolved in hydrate of potas- sium, a new compound (aluminiate of potassium) is formed, the aluminium forming part of the acid- A1 2 H 3 O 3 + KHO = KA1 2 O 2 . H 2 O + H 2 O. The hydrate may be again obtained from the solu- tion by adding chloride of ammonium.thus KA1 2 H 2 3 + NH 4 C1 = A1 2 H 3 3 + KC1 + NH 3 . v This reaction is explained in note 8. S A sulphide is first formed in the reaction with sulphide of ammonium, which is immediately decom posed by water into the white hydrate and hydro sulphuric acid gas. e It will be observed that the hydrate is a constanl result of reactions with even the most varied reagents and aluminium salts. The hydrate in this group generally is an insoluble salt, and its formation is very general. t The solution of aluminic chloride and that o sulphate of potassium should be hot and concentratec (by evaporation). n This salt is the type of the true alums. All true alums have 12 eqs of water of crystallisation : [Al 2 K(SO 4 )3+12aqJ. a The soluble salt formed with sulphate of potas- sium is one of the alums (chrome-alum) having the formula KCrs(SO4)2+12aq. 33 III. THEIR SALTS, AS HYDEATES BY HYDRATE OF AMMONIUM. IRON (Ferric salts). Perchloride of Iron. IRON (Ferrous salts). Protoaulphate of Iron. red-brown Fe 2 H 3 o 3 insol. in excess of hydrate of ammonium, insol. in chloride of ammonium. green- White (becomes red) 2FeHO insol in excess of hydrate of ammonium, sol. in chloride of ammonium /3. I. Hydrates. hydrate of potassium re-acts in the same manner as hydrate of ammonium on solu- tions of ferric salts a. hydrate of potassium re-acts in the same manner as hydrate of ammonium, on so- lutions of ferrous salts, except that the whole of the metal is precipitated. II. Hydrates. 2 Fe 8 Cl 3 + 3 (NH 4 ) 2 S = black/3 (Fe 2 ) 2 s 3 insol. in excess of sulphide of ammonium, sol. partially, in water, forming a green solu- tion. Fe 2 S0 4 +(NH 4 ) 2 S = black? Fe 2 s insol. in excess of sulphide of ammonium. sol partially in water, forming a green solu- tion, and reppt. by sulphide of ammo- nium. III. Sulphides. soluble. green coloration?. blue-- 2 Fe 3 Cfdy insol. in hydrochloric acid and in water. IV. Ferri-Cyanides. blue = prussian blue (Fe 2 ) 2 Cfy 3 sol. in nitric acid. sol. in hydrate of potassium. 3 Fe 2 S0 4 + 4 K 2 Cfy = Whites 2KFe 3 Cfy 2 nitric acid converts it into prussian blue, sol. in hydrate of potassium. V. Ferro-Cyanides. soluble. soluble. VI. Double Sulphates. VII. Silicate. a The ppt. in this case always contains a portion of the alkaline precipitant, which is not removed by washing. /3 This ppt. is only obtained when a solution of ferric chloride is added to sulphide of ammonium, otherwise a ferrous sulphide is thrown down together with sulphur. Hydrosulphuric acid reduces ferric to ferrous salts, with separation of sulphur if the solution is acid or neutral. If alkaline a ppt. is formed. Both ferrous and ferric salts behave in the same manner with sulphide of ammonium, as the members of Group IV.; hence by some chemists iron is included as a member of that group. y This coloration appears to depend upon the pre- sence of a trace of proto- or ferrous salt, and usually acquires a tinge of brown. It is best seen in dilute solutions. a Only half the iron is precipitated, for the ammo- nium salt formed combines with part of the unchanged ferrous salt, producing a double salt (FeCl.NEUCl), which is not decomposed by the excess of hydrate of ammonium present (see Magnesium IV). ft It is clear from the reactions given above that if chloride of ammonium is present in a solution of a ferrous salt, no ppt. will occur on the addition of hydrate of ammonium, hence ferrous salts really belong to Group IV., but in actual analysis the pre- caution is adopted of peroxidising (by nitric acid) any ferrous salt which may be present in the solution to be tested, before adding hydrate of ammonium as a group test. It is thus converted into a ferric salt, and will behave with the group test, as other members of this group. The desirability of contrasting these two classes of salts of iron will be a sufficient reason for placing them together here. 7 Hydrosulphuric acid does not precipitate acid or neutral solutions of ferrous salts. The sulphide is precipitated from an alkaline solution by this reagent. fi Turns blue (prussian blue) on exposure to air. 34 GROUP METALS WHICH AKE PRECIPITATED FROM SOLUTIONS OF MANGANESE. Sulphate of Manganese ZINC. Sulphate of Zinc. Sulphide of Ammonium. Mn 2 SO 4 + (NH 4 ) 2 Sa = flesh-coloured Mn 2 S sol. in most acids. sol. in acetic acid (if concentrated). Zn 2 S0 4 +(NH 4 ) 2 Sa = white sol. in most acids insol. in acetic acid. Zn 2 s II. Hydrate of Potassium. whitishs insol. in excess of hydrate of potassium. White (gelatinous) sol. in excess of hydrate of potassium. III. Carbonate of Ammonium. Mn 2 S0 4 + (NH 4 ) 2 C0 3 = pink-white Mn 2 co 3 sol. in chloride of ammonium. insol. in excess of carbonate of ammonium. 5Zn 2 SOJ + [-M(NH 4 ) 2 C0 3 = 6H 2 ) White 7 2(Zn 2 C0 3 . sZ sol. in chloride of ammonium. sol. in excess of carbonate of ammonium. IV. Cyanide of Potassium. dirty yellow -zMnCy sol. in excess of cyanide of potassium e. Zn 2 SO 4 +2KCy white sol in excess of cyanide of potassium. V. Hydrosul- phuric Acid in a solution acidified with Acetic Acid. Zn 2 S0 4 + 2HC J H 3 2 = H 2 S0 4 + 2ZnC 2 H 3 O 2 acetic acid and i ZnC 2 H 3 2 + H 2 O + H 2 S = white Zn 2 s,H 2 o a Hydrosulphuric acid precipitates alkaline solutions of manganous salts, but not acid or neutral solutions. /3 Turns brown on exposure to air : the colour of the above ppt. is extremely characteristic. y With hydrate of ammonium only half the man- ganese is precipitated, the other half forming with the salt already produced by the first half and hydrate of ammonium, a soluble compound which is not re-pre- cipitated by excess of the precipitant. Presence of chloride of ammonium prevents the precipitation by hydrate of ammonium altogether. S Turns black on exposure to air. e Forms a brown solution. a Hydrosulphuric acid partially precipitates zinc from neutral and entirely from alkaline solutions. In all acid solutions, except acetic acid (see V.), no ppt. occurs. The same reaction occurs with hydrate of ammo- nium as in the case of manganous salts (see Manganese, note y). y The ppt. is a mixed hydrate and carbonate, and since some carbonic anhydride is liberated, which retains a portion of carbonate of zinc in solution, boiling facilitating the escape of carbonic anhydride, precipitation is more complete. IV. THEIR SALTS, AS SULPHIDES BY SULPHIDE OF AMMONIUM. COBALT. Nitrate of Cobalt. NICKEL. Protosulphate of Nickel. black sol. in nitre-hydrochloric acid. insol in acetic acid. .Co S CoN0 3 + KHO/3 blue? CoHO insol. in excess of hydrate of potassium. loCoNCU + U 5 (NH 4 ) 2 C0 3 = 6H 2 J peach coloured 2 (Co 2 G0 3 . sol in excess of carbonate of ammonium Ni 2 S0 4 + (NH 4 ) 2 Sa = black /s Ni 2 s sol. in nitro-hydrochloric acid. insol. in acetic acid. Ni 2 S0 4 +2KHO < and molybdic acids with unknown) ) ( ammonium insol. in dilute acids. sol. in alkalies and their carbonates. VI. Heated with Concentrated H 2 S0 4 , alone and with other reagents Shining scales crystallise out on cooling. Test. Treat the scales with alcohol ignite ; "burn with, a green flamed. and a Phosphoric anhydride (P 2 0s) when dissolved in water may form three different hydrogen salts accord- ing to the conditions under which the solution takes place. These are PjjO5+H 2 O = 2HPO3 meta- or monobasic phosphoric acid. P2O5+2H 2 O = H 4 P 2 O7 pyro- or bibasic phosphoric acid. P 2 O5-t-2H 2 = 3H3PO4 ortho- or tribasic phosphoric acid. The latter is only of sufficient importance to be con- sidered here. ft The formula of this salt is uncertain. The ppt. forms in neutral, slightly alkaline, or solutions con- taining free acetic acid. If the solution contains hy- drochloric or any other mineral acid, this may be replaced by acetic acid, by addition of acetate of potassium or sodium in excess presence of tartaric acid and certain organic matters prevent the re- action. y The addition of some hydrate of ammonium should precede that of nitric acid. Care should be taken not to operate with excess of phosphate. a This may be considered as representing the type of the monoborates. The anhydride combined with a monoborate n:ay be taken as the type of the bi- borates thus BogO 3 + 2HBoO 2 = H^Bo-iOr. A solution of boracic acid, or of an alkaline borate, turns turmeric paper red. (This reaction should be con- trasted with the effect of other acids.) /3 Not reppt only if excess of hydrochloric acid is present. y Only precipitated from concentrated solutions. Before concentrating dilute solutions of boracic acid, the latter must be combined with an alkali, other- wise a large portion would volatilize on evaporation. 8 The green coloration is most apparent at the edge of the flame when viewed against a dark background. Salts of copper also manifest this characteristic colour. The presence of metallic chlorides gives rise to the formation of chloride of ethyl, which also pro- duces a green coloration of the flame. 47 SECTION in. OF THEIR SALTS, BY CHLORIDE OF BARIUM. CHLORIC ACID, WITHOUT DECOMPOSITION. OXALIC ACID (H 2 C a 4 ). HYDROFLUORIC ACID (HF). Oxalate of Ammonium. Fluoride of Potassium. (NH 4 ) 2 C 2 O 4 a white Ba 2 C 2 4 sol. in hydrochloric acid, reppt. by hydrate of ammonium, sol. sparingly in water. KF + BaCl white BaF sol. in hydrochloric acid, reppt. by hydrate of ammonium, in sol. iu water. I. Barium Salts. white/3 sol. in hydrochloric acid, insol. in acetic acid. Ca 2 C 2 4 KF + CaCl White = fluor spar CaF sol. sparingly in hydrochloric acid, reppt. by hydrate of ammonium, insol. in acetic acid. II. Calcium Salts. white Ag 2 c 2 o 4 sol. in nitric acid, and hydrate of ammonium III. Argentic Salts. IV. Ferric Salt. Effervescence. (evolution of carbonic oxide and anhydride.) H 2 C 2 4 + H 2 S0 4 = H 2 S0 4 . H 2 O + CO + CO S No blackening of the compound y. Test. Ignite the evolved gases ; carbonic oxide burns with blue flame. ii. HjS0 4 + Mn 2 O 2 + an oxalate. Effervescence. (evolution of carbonic anhydride only.) o If oxalic acid is used, the acid oxalate is formed (BaHC 2 O4) ; the reactions with solvents are the same in each case. ft In dilute solutions the ppt. appears only after some time. Oxalates of chromium and iron are not precipitated by chloride of calcium, as they form soluble double salts with oxalate of calcium. y This reaction is characteristic, since most complex acid radicals (ferrocyanide excepted) blacken as well as yield carbonic oxide. Dense fumes, (in moist air.) 2 S0 4 =j2HF_+ K 2 SO< _ fumes Tests, (a) Pungent odour. (b) Corrosive action on glassy. 6HF + Si 2 O 3 = 2SiF 3 + 3H 2 O. ii. H 2 S0 4 + Sand (Si 3 3 ) + fluoride (the pro- ducts being conveyed into waterS). Deposit Of Silica, (gelatinous ppt.) 3SiF 3 + sH 2 O = HSiOg + H 8 Si 2 F 8 . VI. Decompositions. ppt. Test. Add chloride of barium to filtrate from HSi0 2 ppt. ; ppt. of jluosilicate of barium (Ba 3 Si 2 F 9 ). a Addition of hydrate of ammonium promotes pre- cipitation, which usually without this precaution is hardly perceptible. ft This reaction cannot be observed if the experiment is conducted in a glass vessel, or if silicon is present in any form. If silica is present, or the compound is not decomposable by sulphuric acid, the following plan must be adopted: "Fuse the substance with carbo- nate of sodium and potassium ^dissolve the fused mass in water precipitate the silica by carbonate of ammonium and filter it off neutralise the filtrate with acetic acid, and add chloride of calcium." v The etching property of hydrofluoric acid de- pends on the remarkable affinity of fluorine for sili- con. The finely divided fluoride should be placed in a platinum crucible, concentrated sulphuric acid poured on it, and the whole covered with a glass coated with wax through which a device has been scratched. The wax may afterwards be removed by turpentine, when the etching will be plainly visible 8CaF + 4H 2 SO 4 + Si 2 Os=2HF + 2SiFa + 4Ca 2 SO 4 + 3H 2 O, Hydrofluoric Acid is first formed, and this reacts upon the Silica of the glass. (See Hydrofluo-silicic Acid, p. 44, note ft.) fi This experiment may be performed in a test-tube furnished with a cork and bent tube, the latter dipping into mercury, covered with a layer of water. The apparatus must be perfectly dry for obvious reasons. To detect very small quantities of hydrofluoric acid, the delivery tube may be wetted internally, when the deposit of silica in minute quantity will be discovered. 48 GROUP I. ACIDS, WHICH AEE PKECIPITATED FROM ALKALINE OR NEUTRAL ACID SOLUTIONS OF THEIR SALTS CHROMIC ACID (HO0 2 )*. Chromate of Potassium. SULPHUROUS ACID (H 2 S0 3 ). Sulphite of Ammonium. I. Chloride of Barium. KCr0 2 + BaCl tinlp wpllnwr T?aOrO (NH 4 ) 2 S0 3 + 2BaCl = white Ba 2 S0 3 sol. in hydrochloric and nitric acid, reppt. from solution in the former by hydrate of ammonium, insol. in water. sol. in hydrochloric acid a, not reppt. by hy- drate of ammonium if boiled to expel the sulphurous acid. II. Nitrate of Silver. KCr0 2 + AgN0 3 Crimson (crystalline) ... AgCr0 2 (NH 4 ) 2 S0 3 + 2AgN0 3 = white (granular) Ag 2 S0 3 sol. in nitric acid and hydrate of ammonium. becomes dark grey when boiled /3. sol. in hydrate of ammonium. in. Acetate of Lead. KCr0 2 +PbC 2 H 3 O 2 = VellOW PbCrO 2 (NH 4 ) 2 S0 3 + 2PbC 2 H 3 O 2 = white Pb a so s insol. in water and chloride of ammonium, sol. in nitric acid and hydrate of potassium. insol. in water. IV. Hydrosulphu- ric Acid Gas, passed through a solution. i. Acid solution (HC1) of a chromate. 4 KCr0 2 + loHCl + sH 2 S = 2Cr 2 Cl 3 + 5H 2 S0 3 7 + 5 H 2 S =H 2 S 5 6 + white-yellow 58 (ppt.) / ii. Neutral or alkaline solution of a chromate. 4 KCr0 2 + SH 8 S = 3 S (ppt.) + greenjS ,2Cr 2 H 3 o 3 Hydrochloric Acid. The reaction is similar to that exhibited by sulphuric acid and a chromate. Chlorine is evolved. (NH 4 ) 2 SO 3 + 2HC1 =SO 2 + H 2 + 2NH 4 C1 no precipitation of sulphur S. Zinc and Hydrochloric Acid. Evolution of H 2 S gas. Test. Contact with paper moistened with acetate of lead ; .. paper is blackened. Heated with Cone ' H,SO t . Evolution of Oxygen 7. Test. Apply a piece of kindled wood to escap- ing gas ; bursts into flame. Effervescence. (evolution of sulphurous anhydride.) Test. Odour of burning sulphur. ^ ' - a. The sesquichloride of chromium has a green colour : this together with the pale yellow ppt. of sulphur is characteristic of chromic salts, and betrays their pre- sence in the systematic course of analysis for bases. /3 In this case a green ppt. of chromic hydrate accom- panies the sulphur ppt. V K 2 Cr 4 07 + 4H 2 SO 4 = K 2 S0 4 + (Cr 2 ) 2 (SO 4 ) 3 bichromate + 4H 2 O + Os * The hydrogen salt has not been isolated. The an- hydride (CraOa) is obtained in the form of dark crim- soa crystals, from an aqueous solution of chromic acid. a If this hydrochloric acid solution is boiled with ni- tric acid, the sulphite is converted into sulphate ; this being an insoluble salt is precipitated. j3 The white sulphite is decomposed into sulphuric acid and metallic silver, y This decomposition only occurs in the case of free sulphurous acid. If the experiment is performed with a sulphite, the latter must oe previously treated with hydrochloric acid, as in the next reaction. S This reaction with hydrochloric acid, without pre- cipitation of sulphur, affords a means of distinguishing sulphurous from hyposulphurous acid. SECTION iv. SOLUTIONS OF THEIR SALTS, BY CHLORIDE OF BARIUM. DECOMPOSED BY- HYDROSULPHURIC ACID. HYPOSULPHUROUSACID(H 2 S a 3 )- IODIC ACID (HI0 3 ). Hyposulphite of Sodium. lodate of Potassium. Na 2 S 2 3 + 2BaCl = White Ba s S 2 3 KI0 3 + BaCl white (granular) BalO I. Barium Salt. sol. in hydrochloric acid a. sol in boiling water. sol. in nitric acid, sol. sparingly in water. NajS.Oa + aAgNO, = White Ag 2 S 2 3 KI0 3 + AgN0 3 white--- AglOg II. Argentic Salt. becomes yellow, red, and finally blackjS. sol. in excess of hyposulphite of sodium. sol. in hydrate of ammonium, sol. sparingly in nitric acid. Na 2 S 2 O 3 + 2PbC 2 H 3 2 = white (becomes black when cool) 7-..Pb 2 S 2 3 sol. in alkaline hyposulphites. KIO 3 + PbC 2 H 3 2 = white Pblo 3 III. Plumbic Salt. sol. sparingly in water and nitric acid. This acid is introduced as a member of Sec- tion I. because since in practice the members of this section are detected in testing for bases, and the addition of hydrosulphuric acid is preceded by hy- drochloric acid, the mere addition of the latter is sufficient to decompose the solution of a hyposulphite with separation of sulphur. 2KI0 3 + 3 H S S = H 2 S0 4 + WViitp vpllowa... ,...28 (ppt.) IV. Decompositions. Na 2 S 2 3 +2HCl = S0 2 + Reaction the same as in the case of sul- phurous acid. Evolution of sulphurous anhydride. o Nitric acid converts the ppt. into sulphate, which is insoluble. ft The change in colour results from decomposition of the sulphite, and formation of the black sulphide of silver, v Nitric acid converts this ppt. into sulphate. S Hyposulphurous acid is first set free, and rapidly decomposed into sulphurous acid and sulphur. The sulphurous acid further decomposes into water and sulphurous anhydride, the presence of the latter being revealed by its characteristic odour. a The decomposition of iodic acid by hydrosulphuric acid is attended with evolution of free iodine, and subsequent formation of hydriodic acid. 50 GKOUP II. ACIDS, WHICH AKE PRECIPITATED FROM SOLUTIONS THE PRECIPITATE SOLUBLE IN HYDROCHLORIC ACID HYDROBROMIC ACID (HC1). (HBr). Chloride of Sodium. Bromide of Potassium. I. Nitrate of Silver. NaCl + AgNO 3 White (curdy)a AgCl sol. in hydrate of ammonium, reppt. by nitric acid. insol. in dilute nitric acid, fuses without decomposition on being heated. KBr+AgNO 3 White-yellow (curdy) AgBr sol. in hydrate of ammonium, reppt. by nitric acid. insol. in dilute nitric acid, fuses without decomposition on being heated. II. Ferrous Sul- phate and Ferric Chlo- ride. III. Sulphide of Ammonium. IV. Treated with Cone ' Sul- phuric Acid, alone and with other reagents. i. Solid chloride + H 2 S0 4 p. Fumes Of HC1 gas. (effervescence.) 2NaCl + H 2 S0 4 =2HC1+ Na 2 S0 4 ii. Solid chloride + H 2 S0 4 + a chromate y. Red fumes, condensing to a blood-red liquid (chloro-chro- mic acid) 8. NaCl + H 2 SO 4 + KCr0 2 = KNaSO 4 + H 2 + red liquid ........................ CrOCl Tests, (a) Add hydrate of ammonium to liquid colour becomes yellow. CrOCl + 2NH 4 HO = NH 4 C1 r NH 4 . CrO 2 + H 2 O (b) Add slight excess of acetic acid to the yellow solution : then nitrate of silver ; crimson ppt. NH 4 CrO 2 + AgNO 3 = AgCrOg -r NH 4 N0 3 iii. Solid chloride + H 2 SO 4 Evolution of chlorine gas. sNaCl + H 2 S0 4 = i HC1 + Na 2 S0 4 and 4HC1 + Mn 2 O 3 = C1 2 + 2MnCl + 2H 2 0. Tests. Odour. Colour. Bleaches moist vege- table colours. i. Solid bromide + H 2 SO 4 a. Evolution of bromine vapour . 2KBr + H 2 S0 4 = 2 HBr + K 2 S0 4 y. and i HBr + H 2 SO 4 - 2 Br + H 2 S0 3 4- H 2 0. Tests, (a) Pungent odour. Red-brown colour, (b) Contact with starch-paste on a glass rod ; yellow or orange colour. ii. Solid bromide + H 2 S0 4 + a chromate. Evolution of bromine vapours. (condenses to red-brown liquid.) 2KBr+ H 2 SO 4 + KCrO 2 = 2 HBr + K 2 SO 4 and [ + KCrO s 2HBr + H 2 S0 4 = 2Br + H 2 .SO ? + H 2 O Tests, (a) Add hydrate of ammonium to liquid ; becomes colourless. (b) Add nitrate of silver to the colour- less solution ; white ppt. iii. Soh'd bromide + H 2 SO 4 + Mn 2 2 . Evolution of bromine vapour. [the reaction is similar with hydrochloric acid.] Test, as above, i. a This put. becomes violet on exposure to light *. ft The chlorides of mercury, silver, lead and tin re- sist decomposition by sulphuric acid. y (Solid chlorides in presence of a nitrate, when heated with concentrated sulphuric acid, evolve chlo- rine and nitrous fumes.) The chloride in this experiment should be perfectly dry, as also the apparatus in which it is performed. The gas may be conducted from the test tube in which generated, to another surrounded with water, to con- dense it. Chloro-chromic acid is readily decomposed by water. S The formula is sometimes written . Cr 2 O 3 = 3(CrOCl). * Most of the acids of Group I. are also precipitated by nitrate of silver, but the silver salts of Group I. are sufficiently distinguished from those of Group II. by the solubility of the former in dilute nitric acid. a With dilute sulphuric acid, hydrobromic acid gas is evolved. /3 Chlorine-water (not in excess) also liberates bro- mine when added to a solution of a bromide. The bro- mine dissolves in the water, rendering it yellow or orange according to quantity present. If this solution is agitated with some ether, the latter dissolves out the bromine from the water, and on standing rises with it to the surface of the liquid, as a red-brown layer. This layer, if decanted and agitated with hydrate of potassium, is decolorised from formation of bromate of potassium. On evaporation and ignition the latter is converted into bromide of potassium. (This reaction will not distinguish between oromine and iodine.) y If sulphuric acid is added to a bromide, in the cold, this reaction only takes place ; hydrobromic acid being liberated, heat causes the further decomposition. & No b ron 10 -chromic acid is known. 51 SECTION i. OF THEIE SALTS, BY NITRATE OF SILVER. HYDRATE OF AMMONIUM. HYDROCYANIC ACID HYDRO-FERRI-CYANIC ACID (HCy). (H 3 Fe 2 Cy e =H 3 Cfdy). Cyanide of Potassium. Ferricyanide of Potassium. White (curdy) AgCy sol. in hydrate of ammonium, and conc a nitric acid. insol. in dilute nitric acid, decomposed on ignition with separation of metallic silver and cyanogen. orange Ag a Cfdy sol. in hydrate of ammonium. insol. in nitric acid. decomposed by heat with separation of metal- lic silver. I. Argentic A mixture of ferrous sulphate and feme chlo- ride a. 6KCy + Fe 2 S0 4 = 2 (K 2 FeCy 3 ) + K 2 S0 4 and blue = Prussian blue ..... (Fe 2 ) 2 (FeCy 3 ) 3 2 K 3 Cfdy+ 3 Fe 2 S0 4 = blue 2Fe a Cfdy insol. in water and hydrochloric acid, the ferric salt is soluble a. II. Ferrous and Ferric Salts. KCy + HCl and HCy + NH 4 HS + S = NH 4 Cy S + H 2 S The sulphocyanide of ammonium is treated with ferric chloride. III. Ferric Sulpho- cyanide. blood-red solution ....... Fe 2 (CyS) 3 -t- 3NH 4 C1 i. Solid cyanide + H 2 S0 4 7. Evolution of carbonic oxide. (NH 4 ) 2 S0 4 2H 2 S0 4 gas Test. Ignite the gas ; burns with blue flame. [With dilute sulphuric acid or hydrochloric acid, cyanides evolve hydrocyanic acid gas (see above III) : much caution should be exercised in performing this experi- ment from the poisonous nature of the vapours. They burn with a blue flame.] Ferricyanides behave like cyanides with con- centrated sulphuric acid and with dilute sulphuric or hydrochloric acid. IV. Decomposition. a The addition of hydrate of potassium must pre- cede that of the mixed salts of iron (since the reaction does not occur in presence of free hydrocyanic acid). And since the alkali itself forms a dense ppt. of fer- rous and ferric hydrate, which obscures the Prussian blue ppt., it is necessary further to dissolve the hydrate ppt. in some dilute hydrochloric acid. This experiment should be performed in the fol- lowing manner place the cyanide in a watch-glass; add a few drops of hydrochloric acid ; invert another watch-glass over the first, the interior being moistened with sulphide of ammonium containing an excess of sulphur. After the sulphocyanide of ammonium is formed, evaporate all remaining sulphide of ammo- nium from the upper watch-glass in a water-bath, then add the ferric chloride to the residue. v To detect hydrocyanic acid in cyanide of mercury neither this method nor the preceding one will apply. The mercury must first be precipitated as sulphide by hydrosulphuric acid. a The solution of a ferricyanide after adding ferric chloride assumes a green tint. This coloration appears ;o depend on the invariable presence in practice of a .race of a ferrous salt. GROUP II. ACIDS, WHICH ABE PRECIPITATED FROM SOLUTIONS THE PRECIPITATE INSOLUBLE HYDRIODIC ACID (HI). Iodide of Potassium. HYDROSULPHURIC ACID (H 2 S). Sulphide of Ammonium. Nitrate of Silver. KI + AgN0 3 pale -yellow (crystalline) a Agl !nsol. in hydrate of ammonium /3. insol. in dilute nitric acid^. black Ag 2 s insol. in hydrate of ammonium, and cold di- lute nitric acid. sol. in boiling nitric acid, with separation of sulphur. II. Acetate of Lead. KI + PbC 2 H 3 2 OIEinge (crystalline) Pbl sol. in boiling water, and in chloride of ammo- nium, insol. in hydrate of ammonium. black a Pb 2 s insol. in cold water and dilute acids. III. Cuprous Sulphate. KI + (Cu 2 ) 2 S0 4 8 = white-brown *Cn 2 i decomposed by nitric or sulphuric acid with evolution of free iodine. black IV. Cupric ate. [(NH 4 ) Cupi Sulph = C U2 S-I-(NH 4 ) 2 S04] black v. Ferrous Sulphate. [(NH 4 ) = Fe 2 S + (NH 4 ) 2 SO<| black VI. Ferric Chloride. [3(NH 4 ) 2 S-rsFe 2 Cl 3 = (Fe 2 ) 2 S 3 + 6NH 4 C1] black VII. Heated with Concentrated Sulphuric Acid. Solid iodide + H 2 S0 4 Evolution of iodine vapour. (condenses, if much iodine, to black crystals.) KI + H 2 S0 4 = 2! + K 2 S0 4 * Test. Contact with starch paste on a glass rod ; the starch becomes blue. Sulphide + H 2 S0 4 or HCly. Evolution of H 2 S gas 5. (NH 4 ) 2 S + H 2 S0 4 = H 2 S + (NH 4 ) 2 S0 4 Test. Contact with paper moistened with acetate of lead; the paper is blackened. (Pb 2 S) Odour. Heated with Concentrated Nitric Acid. (See note e.) Solid sulphide + HN0 3 e. Separation of sulphur, with formation of sulphuric acid. 2Fe 2 S+ ioHN0 3 =2Fe 2 (N0 3 ) 3 f+ 4 H 2 O + a The ppt. becomes dark on exposure to light. Addition of hydrate^ of ammonium decolorises the solution. 5^\> y Coned, nitric acid decomposes the ppt. with sepa ration of free iodine. 5 The cuprous salt is generally formed for this pur- pose by adding ferrous sulphate to cupric sulphate, thus, 2Cu 2 S04 + 2Fe 2 S0 4 =(Cu 2 ) 2 SO 4 +(Fe 2 ) 2 (SO 4 )3. Chlorine reacts with iodides as with bromides (see p. 50). The colour of the ether solution is violet or red-brown. The iodine may be converted into iodide of potassium, and tested by nitrate of silver. ' Many other compounds decompose iodides, with evolution of free iodine, e.g. bromine, nitric acid, nitrous acid, hydrochloric acid, sulphuric acid, and peroxide of manganese. According as the iodine is in excess or less in quantity, so is it precipitated in the form of black crystals, or given off as violet vapours. f If much iodine is present the colour is black. * The intermediate reaction, with HI and H 2 S04 oc- curs here, as in the case of HBr, Bromine (p. 50). a This reaction is very characteristic; a piece of paper moistened with a soluble salt of lead (acetate) manifests it in presence of hydrosulphuric acid sus- pended in the gaseous form in the air. ft This salt may be formed by adding stannous chloride to a solution of cupric chloride, or by boiling metallic copper with an acid solution of cupric chloride. y Many sulphides are decomposed by dilute sul- phuric or hydrochloric acid, e.g. sulphides of the alkalies, alkaline earths, iron, manganese and zinc. Others, as sulphides of cobalt, nickel, antimony, lead, require concentrated acid. 8 Some sulphides, e.g. copper, lead, do not evolve this gas when treated with sulphuric or hydrochloric acid. e Sulphide of mercury alone resists the decomposing action of cone 11 nitric acid. It only yields to the action of aqua-regia. f Generally, the action of nitric acid upon decom- posable sulphides, is to form the most highly oxidised combination of which the metal of the sulphide is susceptible ; thus, sulphide of lead yields sulphate sulphide of tin, binoxide. SECTION n. OF THEIR SALTS, BY NITRATE OF SILVER. IN HYDRATE OF AMMONIUM. HYDRO-FERRO-CYANIC ACID HYDRO-SULPHO-CYANIC ACID (H 2 FeCy 3 =H 2 Cfy). (HCNS=HCsy)a. Ferrocyanide of Potassium. Sulphocyanide of Potassium. K 2 FeCy 3 +2AgN0 3 = White Ag 2 FeCy 3 insol. in hydrate of ammonium, insol. in dilute nitric acid, decomposed by heat, with separation of me- tallic silver. KCNS + AgNO 3 white AgCNS insol. in hydrate of ammonium, insol. in dilute nitric acid, decomposed by heat, with separation of me- tallic silver. I. Argentic Salts. White Pb 2 FeCy 3 sol. in chloride of ammonium. insol. in water and hydrate of ammonium. 2 H 3 2 = pale-yellow PbCNS (separating slowly) /3 decomposed by water. II. Plumbic Salts. = (Cu 2 ) 2 FeCy 3 + aKd] white a [KCNS + Cu 2 Cl white III. Cuprous Salts. K 2 FeCy 3 + Cu 2 S0 4 = red-brown Cu 2 FeCy 3 insol. in acids, water, and salts of ammonium. Forms with difficulty 7. IV. Cupric Salts. 4 K 2 FeCy 3 +3Fe 2 S0 4 - White (rapidly becomes blue)..2[KFe 3 (FeCy a ) 2 ] nearly insol. in water. nitric acid converts it into prussian Hue. V. - Ferrous Salts. blue prussian blue. . ..(Fe 2 ) 2 (FeCy 3 ) 3 insol. in water, sol. in nitric acid. Soluble, blood-red colour of solution characteristic, (see Hydrocyanic Acid, p. 51.) VI. Ferric Salts. Solid ferrocyanide/3-)-H 2 S0 4 Evolution of carbonic oxide % (6<70+ 3 (NH 4 ) 2 S0 4 Solid Sulphocyanide -f H 2 S0 4 . Evolution of carbonic oxide, with separation of sulphur. 6H 2 S0 4 Test. Blue flame when ignited. sH B S0 4 K 2 S0 4 +(NH 4 ) 2 S0 4 Yellow ppt. (composition of the ppt. uncertain?.) VII. Decompositions. a The ppt. rapidly becomes brown, being converted into a cupric salt. /S Ferrocyanide of sodium also reacts in this manner. y With dilute sulphuric acid, hydrocyanic acid is evolved from alkaline ferrocyanides, recognised by its odour. The decompositions are not to be relied upon for detecting this acid radical. The reactions of its solutions with ferrous and ferric salts are chiefly em- ployed to distinguish it. Northcote and Church give the following interesting decomposition: Boil a ferrocyanide (not alkaline) with hydrates or carbonates of potassium or sodium ferrocyanide of potassium or sodium is thus formed filter evaporate the solution to'dryness ignite a fused mass is obtained in that portion of the mass soluble in water an alkaline cyanide will be found if tested for (see Hydrocyanic Acid, p. 51); in that portion insoluble in water, after washing and dissolving in hot hydrochloric or nitric acid, iron may be tested for*. Manual of Qualitative Chemical Analysis, p. 345. a This acid is found in the saliva. /3 Converted by hot nitric acid into plumbic sul- phate. y It may be produced in a concentrated solution of Sulphocyanide of potassium, by adding sulphuric acid, and then a saturated solution of cupric sulphate. The ppt. is black, the formula is CuCNS. S Chlorine gas passed into the solution of a Sulpho- cyanide produces a similar ppt. 72 54 GROUP III. ACIDS, WHICH ARE NOT PRECIPITATED FROM SOLUTIONS OF THEIR SALTS, BY CHLORIDE OF BARIUM OR NITRATE OF SILVER. NITRIC ACID (H.V0 3 ). Nitrate of Potassium. CHLORIC ACID (HC10 3 )a. Chlorate of Potassium. I. Ferrous Sulphate. n. Sulpindi- gotic Acid. 2KN0 3 ) + } + ioFe 2 S0 4 / 4 H 2 S0 4 ) brown compound-. 4 Fe 2 S0 4 .N 2 O 2 KN0 3 + H 2 S0 4 + sulpindigotic acid 7. Colour becomes yellow. KCi0 3 + H 2 S0 4 + sulpindigotic acid. Colour becomes yellow. II, III. Cone 1 Sulphuric Acid. Hydrochlo- ric Acid. Solid nitrate + H 2 SO 4 + metallic copper. Evolution of red fumes 5. 6Cul (K 2 S0 4 + 3Cu 2 S0 4 i- 4 H 2 + + 4H 3 S0 4 ) I N 2 2 (nitric oxide) and N 2 2 + O 2 = N 3 4 (peroxide) . ii. Solid nitrate + HC1. Evolution of red fumes and chlorine e . 2KN0 3 + 4HC1 = N 2 4 + C1 2 + 2KC1 + 2H 2 Test. Bleaching power of chlorine. Solid chlorate + H 2 S0 4 (not heated). Evolution of green-yellow gas 1 / 3 - (hypochloric anhydride.) 3KC10 3 ) f CT 8 4 +KC10 4 + + cH 2 SOJ ~t2KHS0 4 + H 2 y. ii. Solid chlorate + HC1 (not heated). Evolution of yellow gas. (euchlorine 5. ) III. Decompo - sitions. Tests. Odour. Explodes in contact with flame IV. Sulphurous Acid. iii. KC10 3 + sulphurous acid. Chlorate is decomposed. Test. Add nitrate of silver; white ppt. e, insoluble in nitric acid f. a All nitrates are soluble in water, therefore they are not precipitated by reagents. ft If a crystal of ferrous sulphate is dropped into the solution of nitrate and acid, a brown ring forms round the crystal. Or the crystal may be dissolved (without heat) in the solution of nitrate, and the acid carefully added, when a brown stratum will appear at the junc- tion of the two liquids. y A few drops only of solution of indigo should be used. S Nitric oxide is first formed, but becomes oxidised by exposure to air, is converted into peroxide, and ap- pears in the form of red fumes. e The solvent powers of nitro-hydrochloric acid (aqua rejjia) depend on the ready decomposition of nitric acid by hydrochloric acid, and simultaneous evolution of free chlorine. 2HNO 3 + 2HC1 = N a 4 -I- 2H 2 O + 2C1. The nascent chlorine exerts a powerfully solvent action, greater than that of nitric or hydrochloric acid separately. a All chlorates are soluble in water, hence they cannot be identified by the formation of precipitates. ft The application of heat, in performing this experi- ment, should be avoided, and small quantities only of chlorate used, since the explosion which attends the decomposition at a high temperature is liable to be dangerous; without heat, a slight crackling occurs during the decomposition, the solution at the same time becoming intensely yellow. Chlorates do not exhibit the reaction with metallic copper which is observed in the case of nitrates. y This is the chief insoluble salt of the perchloric radical. Perchlorates are sufficiently distinguished from chlorates by decomposing with difficulty and not suffering decomposition by sulphurous acid. (See above Iv. and note f.) 8 This gas explodes violently when heated. e The ppt. is a mixed sulphite and chloride of silver. f The ppt. produced by nitrate of silver in a solu- tion of a percMorate treated with sulphurous acid consists entirely of sulphite of silver, and is soluble in nitric acid. IV. ORGANIC ACIDS. GROUP I. ACIDS, WHICH ARE PRECIPITATED FEOM SOLUTIONS OF THEIR SALTS, BY CHLORIDE OF CALCIUM. TARTARIC ACID (H 2 C 4 H 4 6 ). Tartrate of Sodium. CITRIC ACID (H 3 C 8 H 6 7 ). Citrate of Sodium. Chloride of Calcium. Na 2 C 4 H 4 6 -h2CaCl = White (crystalline) a Ca 2 C 4 H 4 O e sol. in hydrate of potassium, reppt. on boil- _ing/3. _ sol. in acetic acid. Na 3 C 6 H 5 7 White (crystalline) a Ca 3 C 6 H 5 7 insol. in hydrate of potassium. sol. in acetic acid. I. Calcium Salts. II. Hydrate of Calcium. White (flocculent, then crystalline).. Ca 2 C 4 H 4 6 sol. in tartaric acid and chloride of ammo- nium, separating again after some time in the crystalline form. No ppt. in cold solutions ; a ppt. forms in boiling solutions, dissolving when cold. II. Calcium Salts. III. Chloride of Barium. IV. Nitrate of Silver. white Ba 2 C 4 H 4 O 6 sol. in salts of ammonium (except the hydrate), sol. in hydrochloric acid. white Ba 3 C 6 H 5 7 sol. in salts of ammonium. sol. in acids and in much water. III. Barium Salts. Na 3 C 4 H 4 6 +2AgN0 3 = White (crystalline) Ag 2 C 4 H 4 6 sol. in hydrate of ammonium 7 and in acids, insol. in water. White (flocculent) Ag 3 C 6 H 5 7 sol. in hydrate of ammonium /3 and in nitric acid, sol. in boiling water. IV. Argentic Salts. V. The solid salt, heated with Conc d H 2 SO 4 Blackening (separation of carbon) and evolution of carbonic oxide s. Blackening only on prolonged boiling, and evolution of carbonic oxide?. v. Decompo- sitions. o Presence of salts of ammonium prevents precipi- tation ; free ammonia promotes it. If hydrate of ammonium is added to a small quantity of tartrate of calcium, and a small crystal of nitrate of silver then added, on cautiously heating the sides of the test-tube become coated with metallic silver. /3 Tartrate of calcium, after being re-precipitated from the boiling solution in hydrate of potassium, again re-dissolves on cooling. y On boiling, this solution becomes black, from the reduction of silver to the metallic state. 8 Sulphurous and carbonic anhydrides are simul- taneously evolved. An odour of burnt sugar is appa- rent on heating. o In dilute solutions, the ppt. only appears on boil- ing, citrate of calcium being less soluble in hot than in cold water. No ppt. is produced with citric acid itself: this must therefore be neutralised by salts of potassium or sodium. Presence of salts of ammonium prevents precipita- tion ; free ammonia promotes it. /S No blackening occurs on boiling. y Sulphurous and carbonic anhydrides are also evolved. Acetic acid is also one of the products of decomposition. 56 ORGANIC GROUP ACIDS, WHICH AEE PRECIPITATED FKOM NEUTRAL SUCCINIC ACID (H 2 C 4 H 4 4 ). BENZOIC ACID (HC 7 H 5 2 ). Succinate of Ammonium. Benzoate of Ammonium. I. Ferric Chloride. 3(NH 4 ) 2 C 4 H 4 4 +sFe 2 Cl 8 = red-brown a... ,...(Fe a ) Q (CJBLO,),? 3(NH 4 .C 7 H 5 2 )+Fe 2 Cl 3 = buff a Fe 2 (C-H 5 2 ) 3 * sol. in hot acetic or succinic acid/3 and in mineral acids, decomposed by hydrate of ammonium. sol. in most acids, decomposed by hydrate of ammonium. n. Nitrate of Silver. (NH 4 ) 2 C 4 H 4 4 + 2AgN0 8 = w hite Ag 2 c 4 H 4 o 4 NH 4 .C 7 H a 2 +AgN0 8 = white AgC 7 H 5 o 2 sol. in hydrate of ammonium and nitric acid, sol. sparingly in water. sol. in hydrate of ammonium and nitric acid, sol. in boiling water. III. Acetate of Lead. (NH 4 ) 2 C 4 H 4 4 + 2PbC 8 H 3 2 = white ...Pb a C,H.0 4 NH 4 .C 7 H 5 2 + PbC 2 H 3 2 = White (after some time)/? PbC 7 H 5 O s sol. in nitric acid, insol. in alcohol. IV. Chloride of Barium. (NH 4 ) 2 C 4 H 4 4 + 2BaCl= white Ba 3 C 4 H 4 04 soluble, even in alcohol. if alcohol is previously added to the solutiony. V. The solid salt heated with Conc d H 2 S0 4 . Volatile, without decomposition. No blackening. Volatile, without decomposition. No blackening. Solution heat- ed with KHO. VI. Solution of Gelatine. a The composition of this ppt. is variable. ft Hence in a solution containing an excess of acid, ferric chloride produces no ppt. y If the solution to be tested consists of free suc- cinic acid it must be neutralised by hydrate of ammo- nium before adding alcohol and chloride of barium. a The whole of the iron is precipitated if ammo- nium is present as above. Hence benzoate of ammo- nium is employed to separate ferrous and ferric salts from a solution in which both are present. The iron may then be removed from the precipitate by hydro- chloric acid, leaving benzoic acid undissolved. Or the latter may be removed by hydrate of ammonium, leaving the iron as ferric hydrate. /3 If benzoic acid is combined with potassium or sodium instead of ammonium, a white flocculent ppt. is thrown down. The ppt. formed above is very slight even after the lapse of some tune. ACIDS. II. SOLUTIONS OF THEIR SALTS, BY FERRIC CHLORIDE. GALLIC ACID (H 3 C 7 H 3 5 ). Gallic Acid. TANNIC ACID (H 3 C 27 H 19 17 ). Tannic Acid. H,C 7 H,O s +Fe,Ca, bluish-black solution a Fe 3 C 7 H 3 o 5 H 3 C 27 H 19 +Fe 2 Cl 3 = bluish-black <* FegC^H ig0 17 Ferric Salts. H,C w H 1B 17 +3AgNO,= red-brown -A-ggC^HijO^ II. Argentic Salts. HsC 7 H 3 5 + 2PbC 2 H 3 2 = white/s Pb 2 HC 7 H 3 o s H 3 C 27 H, 9 17 + 3PbC 8 H 3 2 =-. white Pb 3 CjrHi 8 o 17 ? III. sol. in conc d . acetic acid. Plumbic Salts. H 8 C 7 H 3 6 + BaCl = White BaH 2 C-H 3 O s H 3 C 27 H 19 0, 7 +3BaCl = wliitp BaC^H,nOi IV. sol. sparingly in water. insoluble in water. Barium Salts. Blackening. (separation of carbon.) Dark purple liquid, V. Decom positions . Brown coloration. immediately y. Brown coloration . VI. White viscous ppt. y. Precipitation of Gelatine. a On boiling, the liquid decolorizes with formation of a ferrous salt and escape of carbonic anhydride. ft This ppt. also contains some water of crystalli- sation. If the acetate of lead is in excess the gallic acid is completely precipitated. y From rapid oxidation and formation of a brown colouring matter, the colour first appears yellow. a This constitutes the colouring matter of ink. j3 Oxidation is not so rapid as in the case of gallic acid, hence the coloration is not so immediate. y This reaction is characteristic of tannic acid. Upon it is based the use of bark (which contains tannic acid) in tanning animal skins. 58 ORGANIC ACIDS. GROUP III. ACIDS, WHICH AEE NOT PRECIPITATED FKOM THEIK SOLUTIONS, BY CHLORIDE OF CALCIUM OR FERRIC CHLORIDE. URIC ACID (H 2 C 5 N 4 H 2 3 ). Uric Acid. ACETIC ACID (HC 2 H 3 2 ). Acetate of Potassium. Nitrate of Silver. KC 2 H 3 2 w ^ e (crystalline) AgC 2 H 3 2 so ^ * n hydrate of ammonium. sol. in boiling water, reppt. on cooling. White ppt. (becomes 'black, if heated.) Argentic Salts. II. Ferric Chloride. 3 KC 2 H 3 2 -rFe 2 C] 3 = red-brown solution a Fe 2 (C 2 H 3 o 2 ) 3 on boiling, the iron is precipitated as basic ferric acetate /3. II. Ferric Salt. III. The solid salt heated with Conc d H 2 SO 4 . H 2 S0 4 + acetate + alcohol. Aromatic odour 7. Brown Solution. (Water reprecipitates uric acid.) III. / Decomposi- tion. IV. Hydrate of Ammonium. Solid uric acid dissolved in nitric acid ; solution evaporated to dryness; hydrate of ammonium added in excess. Purple colour a. IV. Murexide. a Addition of hydrochloric acid to a solution which appears red from presence of ferric acetate, renders it yellow. This reaction serves to distinguish between ferric acetate and ferric sulphocyanide (see p. 53J. /3 On boiling, the solution becomes colourless. y The odour is due to the formation of acetic ether Thus KC 2 H 3 0 in presence of the corresponding acid radi- 3. ) cals. 4. Phosphate in presence of the phosphoric radical. 1. Carbonate, white. 2. Carbonate, white. 3. Carbonate, white. 4. a. Not precipitated. Not precipitated. Not precipitated. a Any ferrous salt has been converted into a ferric salt by the addition of nitric acid, and boiling. a Magnesium is not precipitated by carbo- nate of ammonium in presence of chloride of ammonium. 66 OUTLINE OF THE SYSTEMAT Hydrochloric Acid in an acid or neutral solution. Ppt. Pb Hg 2 Boiling water Sol. Hydrosulphuric Acid in an acid solution. Sol. Pb Ppt. Ag Hg 2 Hydrate of Ammonium. Sol~ Ppt. Ppt. Sn Sb As Pb Pt ) special examination with Au \ NH 4 Cl and Fe 2 S0 4 . if Cd Cu Sol. Nitric acid. Chloride of Ammonium. Hydrate of Ammonium. Sulphide of Ammonium. Ppt. Al) Or } and with (P0 4 ). Fe } Ba, Sr, Ca, Mg, with (PO 4 ). Hydrate of Potassium. Ppt. Hg Pb Bi Cd Cu Nitric acid and Sulphuric acid. Sn Sb As HC1 to re-ppt. Carbonate of Ammonium. Ppt. Fe and (Or) Ba, Ca, Sr, Mg, (P0 4 ) HCl to dissolve. Acetate of Potassium. Sol, Al (P0 4 ) Cr (P0 4 ) and (Fe) Boiled for some time. Sol. As Ppt. Sn Sb Hg(reda.byCu) Pb Ignite Sol. Bi Cd Cu Ppt. Fe and (Cr) Fused, for (Cr). Nitro-hydrochloric acid. Marsh's Test. Sol. Ba Ca Sr Mg (P0 4 ) Ppt. Cr(P0 4 ) and (Fe) Sol. Al (P0 4 ) ' Acetic a Fused. volatile Hg residue Pb Hyd. of Ammonium. Ppt. ~~Sol. Bi Cd Cu Sb Special reactions p. 27. H 2 Sgas to re-ppt.* Cyanide of Potassium. Ppt. Cd Sol Cu Cd and Cu as sulphides*. Sulphuric acid. Sol. Cd Ppt. Cu Sn on the zinc in the apparatus. HC1 to dissolve. Mercuric chloride. Greyppt.=Hg 2 Cl. Sn HCl to re-ppt. T HC1 + HN0 3 to dissolve. Solution placed in a H apparatus. Gases passed through Acetate of Lead, and Nitrate of Silver. Residue. Fe II Sol. Cr (P0 4 ) Acetate of Lead to one part. Molyb. Am. to another for (P0). Ppt. Al (P0 4 ) Silicate of Potassium. Sol. (P0 4 ) Ppt. Al Bol. Ag 3 As O 3 neutralize by Hydrate of Ammonium. Yellow ppt. = As As Ppt. Ag 3 Sb Tartaric acid to dissolve. HCl to acidify. Hydrosulphuric acid. Orange ppt. = Sb 2 S 3 Sb Sn on zinc in the generator. HCl to dissolve. Mercuric chloride. Grey ppt. = Hg 2 Cl Sn 67 >URSE OF ANALYSIS FOB BASIC KADICALS. Sol Sulphide of Ammonium. Ppt. Mn Zn Co Kl Hydrochloric acid. Sol. Chloride of Ammonium, Hydrate of Ammonium, Carbonate of Ammonium. Sol Mn Zn ydrate of Potassium. ~~Sol Zn Ppt. Co Ni HC1+ HN0 3 to dissolve. Cyanide of Potassium. Hypochlorite of Sodium. Ppt. Ni Sol Co Ppt. Ba Sr Ca Hydrochloric acid. Hydrofluosilicic acid, and Alcohol. Sol Mg K Na NH 4 Divide into two portions, A and B. Ppt. Ba Sr Ca Ferrocyanide of Potassium. Sol. Sr Hydrate of Ammonium Phosphate of Sodium. Evaporate and ignite. Ppt. Mg Sol (neglect) Vaporized. NH 4 Residue. Water to dissolv( Hydrochloric ack Chloro-platinic aci and Alcohol. S, METHOD OF ANALYSIS FOR GROUP I. HYDROCHLORIC ACID precipitates from acid or neutral solutions, (Lead, Chlorides 01 {., (Silver. Mercurous Chloride. LEAD is not precipitated by hydrochloric acid, from dilute solutions, because chloiide of lead is soluble in much water. If present it will be detected during the course of the analysis for the next group. OXYCHLORIDES OF ANTIMONY AND BISMUTH may be precipitated along with members of this group. They re-dissolve in an excess of hydrochloric acid. EFFERVESCENCE AND EVOLUTION OF GAS, on addition of hydrochloric acid, reveals the presence of the carbonic, hydrosulphuric, or hydrocyanic, acid-radicals. . They will be readily recognised by their characteristic reactions. Hydrochloric acid must be added drop by drop. A few drops will determine the presence or absence of members of this group; if present, excess must be added; if absent, the only object to be attained is the acidification of the solution preparatory to treating it with hydrosulphuric acid. ANALYSIS OF PEECIPITATE PRODUCED BY HYDROCHLORIC ACID, IN AN ACID OR NEUTRAL SOLUTION. The filtrate, which may contain members of other groups, is set aside for further examination. The precipitate is thoroughly washed with cold water. If the washings are added to the filtrate, any appearance of tur- bidity will reveal the presence of Antimony or Bismuth. Lead. Chloride of lead is soluble in boiling water, the whole of the Lead may be dissolved out from the precipitate by boiling with successive portions of water, and separated by decantation or filtration. Test for Lead, in the filtrate or decanted liquid, with sulphuric acid. Chloride of silver is soluble in hydrate of ammonium. Silver may be removed from the residue by treating with hydrate of ammonium and filtra- tion. (If Lead is present and has not been detected, some turbidity will occur in the filtered solution, from formation of a basic salt of lead. It will dissolve in nitric acid, and therefore may be neglected.) Test for Silver, in the filtered solution, with nitric acid. Mercury. Any residue will consist of the black compound formed by hydrate of ammonium and mercurous chloride. Test for Mercury, by fusing the residue with carbonate of sodium. The solution is acid or neu- tral. Add HC1 in excess. i Filter. (Examine filtrate for next group.) Add much H 2 to ppt. Boil. Repeat with fresh portions of H 3 O. i Filter. Wash ppt. thoroughly. Add H 2 S0 4 lo filtrate. White ppt. = Pb 2 S04. Residue from i. (Ag. H; Add NH 4 HO to ppt. Heat. 3 Filter. Add HN0 3 to filtrate. White ppt. =AgN0 3 . Residue from 3. Dry the residue. Heat in tube with Na 2 CO a . Grey sublimate =Hg. 69 METHOD OF ANALYSIS FOE GROUP I. (CONTINUED). TEEATMENT OF AN ALKALINE SOLUTION WITH HYDROCHLORIC ACID. I. The addition of hydrochloric acid to an alkaline solution may produce a precipitate which dissolves in excess of the precipitant. The solution in this case is treated with hydrosulphuric acid gas, as in the regular course, according to the method for Group II. II. A precipitate may form, on adding hydrochloric acid, which is not dissolved in excess of the precipitant, or on boiling. The formation of this precipitate depends on the fact that certain salts, insoluble in water and hydrochloric acid, are held in solution by some alkali or alkaline salt. The latter is decomposed by hydrochloric acid, and the salt held in solution separates, thus : Sb,S, + (NH 4 ) 2 S + 2 HC1 = Sb 2 S 8 + 2 NH 4 C1 + H a S (See Gr. II. sect. I. col. i). solution ppt. solution gas ANALYSIS OF PRECIPITATE PRODUCED BY HYDROCHLORIC ACID IN AN ALKALINE SOLUTION, AND INSOLUBLE IN EXCESS. a. Ppt. without evolution of gas. /* Ppt. with evolution of HS 2 gas alone. 7- Ppt. with evolution of HCy gas, alone or with H 2 S gas. a. o. White. Orange or Yelloiv. PbCl As 2 S 3 Pb 2 S0 4 As 2 S 6 AgCl SbjjSg HSi0 2 SbjSs f " ' ^ a. b. White. Coloured. Due to sulphur, PtS 3 from presence of an AuS 3 alkaline sulphide. SnS 2 Boil, and Sb 2 S 3 Filter. Sb 2 S 5 Presence of an alkaline cyanide or sulphide. Boil with more HC1 or HN0 3 , to expel HCy. Filter. Test for HSK? 2 HSi0 2 separately. < " Test for the others i . Filter. as substances Boil, insoluble in with conc d . water or acids. HC1 + BN0 3 . Ppt. Filtrate. As^S 5 Treat as a sub- Treat with Hg 2 S stance insoluble in NH 4 HO Cu 2 S water or acids. as in Gr. III. Ni a S See Appendix to (p. 74). . ^ Part IV. Filter. Ppt. Filtrate. Treat as a sub- Treat with stance insoluble in H 2 S gas water or acids. as in Gr. II. See Appendix to (p. 70.) Part IV. See Appendix to i. Filter Part IV. (if necessary). Treat the solution with H 2 S, as in Gr. II. If any residue from 2 treat as a substance insolu- ble in water or acids. See Appendix to Part IV. Ppt. Filtrate. Treat with H 2 S Treat with as in Group II., NH 4 HO if sol. in acids; as in Gr. III. otherwise as a sub- (p. 74.) stance insoluble in water or acids. See Appendix to Part IV. III. No precipitate forms, but gas is evolved, on adding hydrochloric acid. The gas smells of H 2 S, and blackens a solution of acetate of lead. Presence of an alkaline sulphide. Boil to expel all H 2 S. Treat with NH 4 HO as in Gr. III. (P- 74.) The gas smells of HCy. Presence of an alkaline cyanide. Boil to expel all HCy. Treat with H 2 S as in Gr. II. (P- 70.) (It will not matter if H 2 S or CO are evolved along with HCy.) The gas is inodorous, and precipitates lime-water. Presence of carbonic acid combined with an alkali. Treat with H 2 S as in Gr. II. (P- 7o.) 92 70 METHOD OF ANALYSIS FOR GROUP II. (Bismuth, Sulphides of < Cadmium, [Copper. Sulphides of Stannous and Stannic, 1 Antimonious and Antimonic, I Sulphides. Arsenious and Arsenic, HYDROSULFHURIC ACID precipitates from a solution in which hydrochloric acid has failed to produce a precipitate, or from the nitrate from the hydrochloric acid precipitate, Mercuric Sulphide. Sulphide of Lead. [Platinum, (Gold. Hydrosulphuric acid is applied in the form of gas, and is passed through the solution for a considerable time, heating at intervals, in order to ensure a complete result. Before passing the gas, it must be ascertained that the solution has been acidified with hydro- chloric acid, otherwise members of the third or fourth group might be precipitated. SEPARATION OF SULPHUR may result from the action of hydrosulphuric acid, due to the reduc- tion of some easily reducible salt of a basic radical which is not precipitated as sulphide by the group-reagent. A copious yellow deposit of sulphur may occur if nitric acid is present. A yellow-white precipitate of sulphur may be due to the presence of a ferric salt. A green colour in the solution indicates the presence of a chromic salt. In such cases tlie precipitate should be invariably further examined. ARSENIC is precipitated from solutions with great difficulty by hydrosulphuric acid. If it has been detected in the preliminary examination, the solution must be largely diluted with water and then fully saturated with the gas, boiling repeatedly. If zinc is present, a portion is liable to be precipitated along with arsenic. If arsenic exists in the form of its arsenic compounds, the addition of sulphurous acid before passing hydrosulphuric acid gas will, by reducing an arsenic to an arseniows salt, ensure complete precipitation. But if lead, barium or strontium are present, sulphurous acid will, from oxidation, cause these to be precipitated as insoluble sulphates. Hence, if the precipitate produced by hydrosulphuric acid gas, after adding sulphurous acid, is not soluble in acids, it must be treated as an insoluble substance, and examined accordingly. Platinum. Gold. EXAMINATION FOR PLATINUM AND GOLD. If one or both of these have been detected In the preliminary examina- tion, they must be sought for specially in a portion of the solution in which hydrochloric acid has failed to produce a precipitate or in the filtrate from the hydrochloric acid precipitate. Their reactions are so characteristic that these metals will be detected in presence of all other basic radicals. All nitric; acid, if present, must be removed by one or two evaporations with hydrochloric acid. Platinum is converted into chloro-platinate by means of chloride of ammonium, and separated by filtration. Gold may be detected in the residual solution by ferrous sulphate or oxalic acid. N.B. This process will occupy some hours to be efficiently performed, as the platinum precipitate forms slowly. Add to a portion of the ori- ginal solution HCl + NH 4 ClorKCl, (After expelling all HNO 3 ). Evaporate to dryness. Treat residue with alcohol. Yellow ppt.=NH 4 PtCl3 or KPtCk Filter. Filtrate. Evaporate to expel alcohol. Add Fe 2 S0 4 to residue. Brown powder =Au, 71 METHOD OF ANALYSIS FOR GROUP II. (CONTINUED). ANALYSIS OF PRECIPITATE PRODUCED BY HYDROSULPHURIC ACID IN AN ACID SOLUTION. Mercury. [Lead.] Bismuth. The filtrate, which may contain members of other groups, is set aside for further examination. The precipitate after being well washed with hot water, containing some hydrosulphuric acid, is boiled with sulphide of ammonium, iu order to separate this group into two sections. PORTION OF PRECIPITATE INSOLUBLE IN SULPHIDE OF AMMONIUM. The insoluble residue is washed thoroughly free from all sulphide of ammonium and boiled with nitric acid. Sulphide of mercury remains as an insoluble residue. Before filtering this from the undissolved portion, sulphuric acid is added, to precipitate any Lead in the form of sulphate, and this removed together with the mercuric sulphide. The insoluble residue is a mixture of Hg a S and Pb 2 SO 4 , but neither will interfere with the detec- tion of the other. A portion of the mixed precipitate is dissolved in nitro-hydrochloric acid, and from this solution Mercury may be obtained as a metallic deposit on the surface of a piece of copper foil. Another portion is ignited on platinum foil or porcelain. Sulphate of lead not being volatile will remain as a white residue upon the foil or porcelain. Cadmium and Copper. (and see next page.) The remaining sulphides (Bismuth, Cadmium and Copper) in solution in nitric acid, are treated with hydrate of ammonium in excess and heat ap- plied. Bismuth is alone precipitated from the solution as hydrate. Test by dissolving in very little hydrochloric acid and adding much water. The solution containing Cadmium and Copper is evaporated nearly to dryness, dissolved in acetic acid and water, and the metals again converted into sulphides by passing hydrosulphuric acid through the solution. Sulphide of copper may then be dissolved by adding cyanide of potas- sium and separated from the insoluble sulphide of cadmium, which remains as a yellow residue. Test for Cadmium by blowpipe. For Copper, by means of ferro-cyanide of potassium, previously adding acetic acid, since other acids if present decompose the precipitate formed. To the solution to be ana- lysed add H 2 S gas. (Observing precautions.) i Filter. (Examine filtrate for next group. Wash ppt. thoroughly with H 2 S water. Boil ppt. with (NH^S. 2 Filter a. Residue from 2. (Hg. Pb. Bi. Cd. Cu.) Wash thoroughly. Boil with HN0 3 , until all red fumes cease. Dilute with H 2 0. Add H 2 S0 4 until no more ppt. forms. 3 Filter. Divide residue into two portions, A and B. A. Dissolve inHCl + HN0 3 . Introduce piece of metallic copper. Metallic coating =Hg. B. Ignite on platinum foil or porcelain. White residue =Pb 2 S0 4 . Filtrate from 3. (Bi. Cd. Cu.) Add NH 4 HO in excess. Heat. 4 Filter. Dry the ppt. slightly. Dissolve in very little HC1. add H 2 0. White ppt. = BiCl 3 . BiaOs. Filtrate from 4. (Cd. Cu.) Evaporate nearly to dryness . Add HC 2 H 3 O 2 and H 2 0. Reppt. by H 2 S gas. Decant the liquid. Add to ppt. KCy. 5 Filter. Yellow residue =Cd 2 S. Confirm by blowpipe. Filtrate from 5. .(Cu Add some acetic acid. Add K 2 Cfy. Brown ppt. =Cu 2 Cfy. a The filtrate, which may con- tain Sb, As or Sn, is treated as on p. 72, or by Hofmann's method, p. 73. 72 METHOD OF ANALYSIS FOR GROUP II. (CONTINUED). METHOD FOE THE SEPARATION OF CADMIUM AND COPPER (HOFMANN). A solution, which may contain both Cadmium and Copper, is acidified (if not already acid) with hydrochloric acid. Hydrosulphuric acid gas is then passed through the solution, to precipi- tate the metals as sulphides. The precipitate must be washed thoroughly and quickly, otherwise sulphide of copper might pass by oxidation into cupric sulphate. Cadmium. The precipitate is boiled with dilute sulphuric acid. Sulphide of cad- mium is thus decomposed, and soluble sulphate of cadmium formed. Sulphide of copper remains undissolved. Test for Cadmium in the solution by hydrosulphuric acid. Copper. The residue is dissolved in nitric acid, excess of hydrate of ammonium added to neutralize the acid, and, finally, excess of acetic acid to prevent decomposition of the precipitate produced by ferrocyanide of. potassium. Test for Copper in the acetic acid solution by ferrocyanide of potassium. To solution to be analysed, add HC1. (If not already acid). Pass H 2 S gas. Wash ppt. thoroughly and quickly, by decantation. Add H 2 S0 4 . Boil. r Filter. PassH 2 S gas through filtrate. Yellow ppt. = Cd 2 S. Residue from i. Cu. Dissolve in HNOs. Add NH 4 HO in excess. Add HC 2 H 3 2 in excess. Add K 2 Cfy. Red-brown ppt.=Cu 2 Cfy. N.B. All the operations in the above method must be performed as rapidly as possible. PORTION OF PRECIPITATE SOLUBLE IN SULPHIDE OF AMMONIUM. Arsenic. The sulphides of Tin, Antimony, and Arsenic, held in solution by sul- phide of ammonium, are reprecipitated as sulphides on the addition of hydrochloric acid. As hydrochloric acid is liable however to produce decomposition and solution as chloride, of a portion of the sulphides, it is advisable to pass some hydrosulphuric acid gas through the solution at the same time. The precipitate by hydrochloric acid must be well washed. The reprecipitated sulphides are treated with carbonate of ammonium, which dissolves only sulphide of arsenic. Arsenic is again precipitated from this solution by hydrochloric acid, and tested by Fresenius' and Babo's test, or the solution may be precipi- tated by hydrochloric acid, the precipitate dissolved in nitro-hydrochloric acid, and tested by Marsh's test (p. 27). Antimony. The undissolved sulphides of antimony and tin, separated by carbonate of ammonium from arsenic, may be dissolved in nitro-hydrochloric acid. Antimony is sought for by means of a Marsh's apparatus (p. 27). Tin. Tin is reduced by zinc in the apparatus at the same time as a black metallic powder. This, if collected, washed, dissolved in hydrochloric acid, and treated with mercuric chloride, yields the characteristic grey precipi- tate (p. 24). After boiling the H 2 S ppt. with (NH 4 ) 2 S, reppt. by HC1, passing some H 2 S gas. Wash the ppt. thoroughly. (Wash by filtration if much ppt. of sulphur.) Add (NH 4 ) 2 C0 3 . i Filter. Arsenicis in the filtrate. * Add HC1 to filtrate. Test ppt. by Fresenius' and Babo's test (p. 29). Or dissolve ppt. in HC1 + HNO 3 . Test by Marsh's lest (p. 27). Residue from I. (Sb. Sn.) AddHCl+HN0 3 . Place solution in a Marsh's apparatus. Antimony if present will be recognised by its reactions. Tin reduced by zinc in the apparatus, as a Black metallic powder. Wash the powder. Dissolve in HC1. Add HgCl. Grey ppt. =Hg 2 Cl. 73 METHOD OF ANALYSIS FOE, GROUP II. (CONTINUED). SEPAEATION OF ANTIMONY, ARSENIC, AND TIN (HOFMANN). A solution supposed to contain either Antimony, Arsenic, or Tin, or all of them, is introduced into the generator of a hydrogen apparatus. (Hydrogen is evolved by the action of sulphuric acid upon zinc, card being taken to have the materials perfectly free from arsenic.) The evolved gases are allowed to pass from the generator, through a solution of acetate of lead, in order to absorb any hydrochloric or hydro- sulphuric acid. Thence they are conducted through a solution of nitrate of silver. Antimony is here precipitated as anjtimonide of silver (Ag 3 Sb), whilst Arsenic, first converted into arsenious acid, is held in solution as arsenite of silver (Ag 3 As0 3 ) by the liberated nitric acid. (p. 25). Arsenic. If the solution is exactly neutralised by hydrate of ammonium, arsenite of silver is precipitated (yellow). Antimony. The precipitate of antimonide of silver may be dissolved in boiling tartaric acid, the solution acidified by nitric acid, and hydrosulphuric acid gas passed through it. An orange precipitate of antimonious sulphide indicates the presence of Antimony. j"in. Tin remains in the generator as a black deposit upon the zinc, toge- ther with some Lead and Antimony (these latter may be neglected). If collected and boiled with hydrochloric acid, chloride* of tin is formed. This yields with mercuric chloride the characteristic grey precipitate of mercurous chloride (p. 24). If the filtrate from 2 (p. 71) is used, Sb, As and Sn will be in the form of acid radicals. Reppt. as sulphides by HC1, passing at same time some H 2 S gas. Collect the ppt. and wash it. Boil the ppt. with HC1+HN0 3 . The solution may be tested as follows. Place the solution in a H apparatus, (Taking precautions in its use). Pass evolved gases through PbC 2 H 3 2 solution. Thence through AgNO 3 solution, until no ppt. forms in the latter. I Filter the AgNO 3 solution. AddNH 4 HO to filtrate, to neutralize exactly. Yellow ppt.=Ag 3 As0 3 . Residue from I. (Sb. Sn.) Boil with tartaric acid. 2 Filter. AddHN0 3 to filtrate. Pass H 2 S gas. Orange ppt. = Sb 2 S 3 . (The residue from 2 consists of Ag). Collect the black deposit on Zn in the generator. Boil with HC1. Filter. Dilute solution with H 2 O. Add a few drops of HgCl. Grey ppt. = Hg 2 Cl. (Presence of Tin.) N.B. It will be necessary in all cases where Tin, Antimony, or Arsenic is detected in the course of analysis, to examine a portion of the original solution according to reactions on pages 24 and 25, to ascertain in what state of oxidation these basic radicals may have been originally present. METHOD OF ANALYSIS FOR GROUP III. HYDRATE OF AMMONIUM, in the presence of chloride of ammonium, precipitates from a solution in which hydrochloric acid and hydrosulphuric acid have failed to produce a precipitate, or in the filtrate from the hydro- sulphuric acid precipitate, Aluminium, ( as hydrates. And as Barium, ") , , as phosphates (borates, fluorides, or oxalates) Chromium, < phosphates in presence Strontium, >. ,. ., ,. , I in presence of the corresponding acid radicals. Iron, (.of the phosphoric radical. Calcium, J ( as phosphate, in presence of the phosphoric Magnesium i [ radical. A small quantity of Manganese may be precipitated with Iron, but will not interfere with the detection of the latter. A portion of the original solution should be tested, before adding the group-reagent, if the pre- sence of Iron is suspected, in order to ascertain in what state of oxidation it exists. The reactions of ferrous and ferric salts with ferro- and ferri- cyanide of potassium respectively, will determine this (p. 33). The filtrate from the hydrosulphuric acid precipitate, or the solution in which that reagent has failed to produce a precipitate, must be thoroughly boiled to expel all trace of the gas, before adding hydrate of ammonium. Otherwise, on subsequently adding nitric acid (to peroxidise Iron), oxidation of sulphur might produce sulphuric acid, and this would precipitate any Barium, Strontium, or pos- sibly Calcium, as insoluble sulphates. NITRIC ACID is then added to the solution to be tested, the whole evaporated to dryness and then ignited. This may be repeated. By this means any Iron present is converted into a ferric salt (even if it were originally present as a ferric salt, hydrosulphuric acid will have reduced it), and hence it will be thrown down by hydrate of ammonium (p. 33). Any OXALIC ACID is at the same time oxidised, and the presence of Barium, Strontium or Calcium as oxalates in the hydrate of ammonium precipitate, is prevented. Any SILICA is also converted by the desiccation into insoluble silicic anhydride (Si a 3 ). If allowed to remain in its soluble form, it might be mistaken for hydrate of aluminium. (The resi- due after evaporation should be ignited slightly, not too strongly, otherwise certain oxides of this group might be rendered insoluble.) The dry residue is dissolved in hydrochloric acid. CHLORIDE OF AMMONIUM is added to the solution in hydrochloric acid. This prevents precipita- tion of Magnesium (except as phosphate in presence of the phosphoric radical) by hydrate of ammonium. MANGANESE may be detected in the hydrate of ammonium precipitate, by fusing a small por- tion with carbonate of sodium and cyanide or nitrate of potassium on platinum foil; a bluish- green residue indicates its presence. THE PHOSPHORIC RADICAL may also be detected in a small portion of the precipitate, by dis- solving in nitric acid, and adding nitrate of silver. Its presence is revealed by a yellow ppt. The absence of this radical will necessitate great abridgement in the following method of analysis. BORATES AND FLUORIDES may be neglected, as sufficient both of the basic and acid radicals will remain to be detected in the appropriate place. 75 METHOD OF ANALYSIS FOR GROUP III. (CONTINUED). ANALYSIS OF PRECIPITATE PRODUCED BY HYDRATE OF AMMONIUM. The jtttrate, which may contain members of other groups, is set asid for further examination. The precipitate must be thoroughly washed until quite free from all trac of ammonia. It is dissolved in dilute hydrochloric or nitric acid. Excess of hydrate of potassium added in the cold will then precipitat Iron (as phosphate or hydrate) together with the phosphates of barium strontium, or calcium. Chromium and Aluminium remaining in solution. Chromium. By long-continued boiling of the solution, Chromium is precipitated, anc Aluminium left in solution. As some Iron, if present, may have passed into solution along with Chromium, it is necessary to examine the precipitate produced on boiling, by fusing a portion with carbonate of sodium and nitrate of potassium Chromium, converted into soluble chromate of sodium, may be dissolvec out by water and tested with acetate of lead. Iron will be detected in the residue. The remaining portion of the precipitate is examined with a view to ascertain whether Chromium existed originally in combination with the phosphoric radical, or otherwise. Aluminium. I D tne solution from which Chromium has been separated by boiling, Aluminium may exist as hydrate or phosphate. The solution is treated with acetic acid in excess. Phosphate of aluminium, if present, being insoluble in acetic acid, will be precipitated. Test for Aluminium, in the solution, with hydrate of ammonium. After removing Aluminium from the precipitate of phosphate of aluminium, by means of silicate of potassium and filtration, the solution may be tested for the phosphoric radical with molybdate of ammonium (p. 46). Iron. The precipitate containing Iron (together possibly with some Manga- nese), and the phosphates of the alkaline earths, is dissolved in hydrochloric acid. Acetate of potassium added in excess precipitates Iron only, as phos- phate (if the phosphoric radical is present), and as basic acetate. A portion of this precipitate should be tested for Chromium, as directed above, unless the latter has been already detected. The other portion is treated with acetic acid. Any residue after adding acetic acid will contain the phosphoric radical, phosphate of iron being insoluble in acetic acid. Test the solution with ferrocyanide of potassium. If the solution to be analysed has been treated previously with H 2 S, boil, to expel all trace of H 2 S. Add HN0 3 , and evaporate to dryness once or twice. Dissolve residue in HC1. Add some NH 4 C1. Then add group reagent, NH 4 HO. I Filter. (Examine filtrate for next group.) Wash the ppt. thoroughly. Dissolve in HC1. Add in the cold, KHO in excess. 2 Filter. Boil the filtrate for some time. 3 Filter. Divide ppt. into two portions, A and B. A. Fuse with Na 2 CO 3 + KN0 3 . Digest with H 2 O. Dissolve residue in HCgHsOs, and test for Fe, with K 2 Cfy To solution add HC 2 H 3 2 , and PbC 2 H 3 O 2 . Yellow ppt. =PbCrO,. B. Dissolve in HCL Add KC 2 H 3 O 2 in excess. Ppt. Solution. [ndicates the Indicates the )hosphate of oxide, chromium. Confirm by NH iHO. Filtrate from 3. Al. Add HC 2 H 3 2 in excess. Dissolve any ppt. so formed, in HCL Add KHO in excess. Add KSi0 2 . White ppt. =Al 2 (Si0 2 ) 3 . The solution may be tested for the phosphoric radical with molybdate of ammonium as in V. p. 46.) The solution after adding HC 2 H 3 O 2 may be tested for Al by NH 4 HO. lesidue from i, [Fe,(Ba,Sr,Ca.)] Dissolve in HCL Add KC 2 H 3 in excess. Filter. (A portion of ppt. is fused for Or. as above.) Add to ppt, HCjjHgO,. Add K 2 Cfy. Blue ppt. =(Fe*) 2 Cfy. (Any residue after adding HC 2 H 3 Oj consists of phosphate of iron.) 'iltrate from 4. xamine for Ba, Sr, and Ca, as on page 77. no 76 METHOD OF ANALYSIS FOR GROUP IV. SULPHIDE OF AMMONIUM precipitates from a solution in which hydrochloric acid, hydrosulphuric acid and hydrate of ammo- nium have failed to produce a precipitate, or from the filtrate from the hydrate of ammonium precipitate, f Manganese, I Zinc, Sulphides of ( Cobalt> iNickel. On filtering the precipitate produced by sulphide of ammonium, the filtrate may appear dark coloured. This is due to the presence of sulphide of nickel, which is soluble to some extent in sulphide of ammonium (Nickel, p. 35, note (3). In this case the sulphide of nickel may be separated from the filtrate by heat, or by evaporating to expel all sulphide of ammonium, and adding hydro- chloric acid. The precipitate so formed should be examined with that thrown down by the group reagent. ANALYSIS OF PEECIPITATE PRODUCED BY SULPHIDE OF AMMONIUM. The filtrate, which may contain members of other groups, is set aside for further examination. Some difficulty may be experienced in obtaining a clear filtrate; repeated filtration can alone effect a satisfactory result. The precipitate must be well washed with water, and some sulphide of ammonium repeatedly added at the same time. Hydrochloric acid is employed to dissolve the sulphides of manganese and zinc, and to separate them from the sulphides of cobalt and nickel. Manganese. Manganese may then be precipitated from the hydrochloric acid solution by means of excess of hydrate of potassium. Test for Manganese by blowpipe, or sulphide of ammonium, in the latter case previously dissolving in an acid (except acetic acid). Zinc. Test for Zinc, in the solution, by hydrosulphuric acid in presence of acetic acid (p. 34). Cobalt and The remaining sulphides of cobalt and nickel may be dissolved in nitro- Nickel. hydrochloric acid, care being taken to employ only just sufficient nitric acid to effect the solution. The metals may be converted into cyanides, and held in solution, by the addition of cyanide of potassium in excess. On boiling the solution with a few drops of hydrochloric acid, cobalticyanide of potassium and cyanide of nickel and potassium are produced (see p. 35, note S). Whilst still boil- ing, if a solution of hypochlorite of sodium in excess is added, the Potassium and Cyanogen are taken up and Nickel is precipitated as black sesquioxide. In this state it may be readily removed from the Cobalt which remains in solution. (Chlorine and mercuric nitrate have also been employed instead of hypo- chlorite of sodium.) . To the solution to be ana- lysed, add (NH^S. i Filter. t (Examine filtrate for next group. // the filtrate is dark coloured, evaporate. Add HC1. Examine the ppt. so formed with that from i.) Wash ppt. from i thoroughly. Add HC1 in the cold. 2 Filter. Boil the filtrate to expel all H ? S. Add KHO in excess. Whitish ppt. =MnHO. Confirm by blowpipe or 3 Filter. Filtrate from 3. (Zn.) Add HC 2 H 3 2 . Pass H 2 S gas. White ppt.=Zn 2 S.H 2 0. Besidue from i. (Co, NL) Test a portion with borax for Co. Add HC1. Boil. Add few drops of HN0 3 , just to dissolve. Add KCy in excess, and few drops of HCL Boil. Add NaCIO in excess, to boiling solution. Black ppt. = (Ni 2 ) 8 8 . 4 Filter. Filtrate from 4. (Co.) Evaporate to dryness. Heat with borax on platinum wire in the blowpipe flame. Blue bead indicates Co. 77 METHOD OF ANALYSIS FOR GROUP V. CARBONATE OF AMMONIUM, in the presence of chloride of ammonium, precipitates from a solution in 'which hydrochloric acid, hydrosulphuric acid, hydrate of ammonium and sulphide of ammonium have failed to produce a precipitate, or from the filtrate from the sulphide of ammonium precipitate, [Barium, Carbonates of < Strontium, I Calcium. CHLORIDE OP AMMONIUM is added, as in the case of Group in., to prevent the precipitation of Magnesium, as it would not be completely thrown down by carbonate of ammonium. HYDRATE OF AMMONIUM is added, previously to the group-reagent, to ensure against an acid solution. The precipitation will be facilitated by the application of heat. ANALYSIS OF PRECIPITATE PRODUCED BY CARBONATE OF AMMONIUM. Barium. Calcium. Strontium. The filtrate, which may contain members of the sixth group, is set aside for further examination. The precipitate is washed, dissolved in hydrochloric acid, and Barium separated as fluosilicate by fluosilicic acid and alcohol. The whole of the Barium may be removed by taking care to evaporate sufficiently with alcohol and to allow time for the separation. Ferrocyanide of potassium will precipitate Calcium from the remaining solution, on boiling. Test for Strontium, in the solution, by sulphate of calcium or oxalic acid, or in the solution evaporated to dryness, by blowpipe. If the solution to be ana- lysed has been treated with (NH 4 ) 2 S, all the latter must be boiled off, and the solu- tion filtered from any ppt. of S. Add NH 4 C1. Add NH 4 HO. Then add group reagent (NH 4 ) 2 C0 3 . , Filter. (Examine filtrate for next group.) Dissolve the ppt. in HC1. Add H 3 Si 2 F 9 and agitate. Evaporate to dryness, digesting with alcohol and H 8 0. White ppt. =Ba 3 Si 2 F 8 . 1... ...Filter. Solution from i. (Ca, Sr.) Evaporate with more H 3 Si 2 F9 and alcohol, to dryness. Treat the residue with water. Filter, from any ppt. of Ba 3 Si 2 F 9 . Add to solution K 2 Cfy. Boil. White ppt. =Ca 2 Cfy. ...Filter. Filtrate from 3. Evaporate to dryness. Test on platinum foil before blow-pipe. Crimson flame indi- cates Sr. (Strontium may also be precipi- tated from the filtrate from 3, by sulphate of calcium or oxalic acid.) 102 78 METHOD OF ANALYSIS FOR GROUP VI. NO PRECIPITATE is produced in solutions containing the members of this group, by the reagents which are employed to precipitate members of the other groups. A solution in which the previous group-reagents have failed to produce a precipitate, or the filtrate from the carbonate of ammonium precipitate, may contain Magnesium, Ammonium, Potassium, Sodium, AMMONIUM will have been already detected, if present, in the preliminary examination. If detected, it must be expelled before proceeding to test for other members of the group. The behaviour of Ammonium and Potassium with those reagents employed to detect the latter are so similar as to render this precaution essential. ... ., ,. , combined with one or more acid radicals. ANALYSIS OF A SOLUTION WHICH MAY CONTAIN THE METALS, MAGNESIUM, POTASSIUM, SODIUM, AND (AMMONIUM). The solution is divided into two portions, A and B. Magnesium. A. Magnesium may be detected in this portion by phosphate of sodium in presence of hydrate of ammonium. Time must be- allowed for the sepa- ration of the Magnesium salt, as the precipitate always forma with difficulty. Ammonium. B. This portion of the solution ia evaporated to dryness, and the residue ignited, until all fuming ceases, to completely expel ammonia. The characteristic reaction with hydrochloric acid will determine this, and at the same time identify the presence of ammonium. A. Add NH 4 HO, and NasHPO 4 . Agitate well and allow to stand some tune. White ppt.=Mg s NH4P0 4 . Potassium. The residue is treated with a small quantity of water. Potassium is converted into chloro-platinate by the addition of hydro-chloro-platinic acid (bi-chloride of platinum) to the solution, together with some alcohol to promote precipitation. Sodium. The remaining solution contains the Sodium salt. The solution may be evaporated to dryness, and Sodium tested for in the residue, before the blowpipe. Care must be taken to have the platinum wire or foil perfectly clean, as even moisture from the fingers may impair the delicacy of the reaction. Divide solution into two portions, A and B. B. Evaporate to dryness. Ignite, until all fuming ceases. (Test fumes with HC1 un a glass rod.) Add to residue H 2 0. i Filter (if necessary). Add to solution HC1 and HPtCl,, and some alcohol. Yellow ppt.=KPtCla. i Filter. Filtrate from 2. Evaporate to drynesa. Test on platinum wire before blowpipe. Yellow flame indicates Na. PART IV. SYSTEMATIC COURSE OF ANALYSIS FOB ACID RADICALS. 80 ANALYSIS OF A SALT OR MIXTURE OF SALTS FOR ACID RADICALS. The Course of Analysis (as in the case of basic radicals) is divided into three stages, or series of processes. Many of the rules laid down, as affecting the systematic course for basic radicals (pages 60 and 61), are no less applicable to and important in the present course for acid radicals. Certain special features demand attention, as an introduction to the course detailed in this Part. I. The preliminary examination. (The substance under analysis being in the solid form.) p. 82. The decompositions effected on submitting a body to a high temperature, either alone or with certain concentrated acids, chiefly hydrochloric acid, nitric acid, or sulphuric acid, and the characteristic colour, odour or reactions of the substances which result from such decomposition, are relied upon to detect the presence of individual acid radicals. More importance is attached to the results of a preliminary examination, as serving to reveal the presence or abs ence of acid radicals, than is assigned to such an examination in the case of basic radicals. This arises from the nature of the reactions of acid radicals with reagents in solution. The presence or otherwise of certain acid radicals will be determined by the cautious observer during the preliminary examination for basic radicals. III. The process of solution. , The explanations already offered upon this part of the analytical course apply in this place. When it is necessary to resort to the action of an acid in order to effect solution, it will usually be found most advantageous to employ nitric acid (as this acid forms no insoluble salts). III. The application of reagents to the solution. The first thing which claims attention under this head is the preparation of the solution to be examined. This preparation becomes necessary, since if certain basic or acid radicals are present in a substance under analysis, and are allowed to remain in a solution, the application of certain reagents would lead to results different from those which would be anticipated. Thus, the presence of carbonic add might lead to the formation of a precipitate, where this result would not only not lead to the detection of the carbonic radical itself, but falsify other results which are looked for. In like manner the presence of any basic radicals, except potassium, sodium, or ammonium, would frequently cause precipitation in a solution, instead of neutralisation merely, when hydrate of ammonium was employed as a reagent. Ammonium, again, must be excluded, in consequence of the solvent action which many of its combinations, especially the chloride, exercise upon salts which it may be desirable to obtain in an insoluble form. In the examination for acid radicals the reagents employed do not effect separation of the acid radicals, to the same extent as was the case with basic radicals. The reagents only serve to identify, as a rule, the presence or absence of individual radicals. The results of the application of general reagents may be regarded as affording so many hints or clues, determining merely the selection of a series of special and confirmatory tests. It would be useless therefore to apply a general reagent to the filtrate from a precipitate thrown down by another general reagent, in a manner similar to that adopted in analysing for basic radicals. The three general reagents, chloride of barium, nitrate of silver, and ferric chloride, employed in the present course, are to be applied to fresh portions of 81 the solution, prepared as directed on page 83. In some instances even the use of a solution prepared in such a manner is proscribed; some special tests are applied to the original solution. It is clear that great economy in the use of material is essential, where the solution to be analysed has to be split up into so many separate portions. The methods for the analysis of acid radicals, given in the following pages, are subject to many modifications dependent on the results of previous examinations. These results are chiefly the nature of the basic radicals found in the solution the solubility of various salts (an aqueous solution which contains barium would not be examined for sulphuric acid, as sulphate of barium is insoluble; a solution in which silver has been detected could not contain hydrochloric acid) the reactions of a solution with vegetable colours. Thus it happens that much forethought, caution, and judgment are requisite on the part of the analyst who wishes to attain success without sacrifice of time and material, when an examination for acid radicals is undertaken. 82 PRELIMINARY EXAMINATION. (ACID RADICALS.) EXP. I. A portion of the powdered substance is heated in a Glass tube open at both ends, and held obliquely in the flame. Kesults of this experiment, as in Exp. I. Basic radicals, page 61. EXP. IL A portion of the powdered substance is treated with 3 or 4 times its bulk of Dilute Hydrochloric acid, avoiding heat. ii. The above mixture is heated (only cautiously if a chlorate is present). An odorous, yellow gas is evolved. The gas explodes in contact with flame. (the reactions in ii. may also be observed here.) Effervescence. The escaping gas is inodorous, and preci- pitates lime-water. Odour of hydrocyanic acid. Odour of hydrosulphuric acid gas. Odour of burning sulphur. Evolution of red fumes (in presence of copper), Chlorate. Carbonate. Cyanide. Ferricyj ide. Sulphide of an alki alkaline earth, ire manganese or zii Sulphite. Hypos phite (or from < oxidation of sulpl ric acidj. Nitrate. EXP. III. A portion of the powdered substance is heated, nearly to boiling, with 3 or 4 times its bulk of Concentrated Sulphuric acid. CONFIBMATOBT TESTS for acid-radicals*. Cyanogen. Vapours passed into solution of KHO ; add Fe 2 S0 4 and Fe 2 Cl 3 ; dissolve any ppt. in HC1 blue ppt. Sulphurous Gas passed into solution of bichromate of radical. potassium green colour. Chlorine. Substance heated with H 2 S0 4 +KCr0 2 ; fumes condensed ; NH 4 HO added to condensed liquid yellow colour. Acetic acid and AgN0 3 added to this crimson ppt. Sulphur. (Sulphide). Paper moistened with acetate of lead held over gas black ppt. Acetic Substance heated with H 2 S0 4 + alcohol ; radical. acetic ether evolved aromatic odour. Nitric Substance + H 2 S0 4 + crystal of Fe 2 S0 4 radical. brown ring round crystal. Fluorine. Substance + H 2 S0 4 + sand ; products con- ducted into water gelatinous ppt. Tannic Substance in solution -f solution of gelatine radical. white viscous ppt. Citric Substance in solution + excess of hydrate of radical. calcium white ppt. on boiling, dissolving when cool. No "blackening of the mixture, Effervescence, with evolution of gases. Gas burns with a blue flame. has odour of burning sulphur. gives white fumes in contact with hydrate of am. on a glass rod. has odour of hydrosulphuric acid gas. has an aromatic odour. Coloured vapours are evolved. Red-brown ; pungent odour ; colour starch-paste, orange. Violet ; colour starch-paste, blue. Greenish-yellow ; detonate. Red. Colourless gases are evolved. Gas kindles burning wood. Pungent fumes are evolved. Fumes give film of silicic acid on wet glass rod. Crystals, as scales, appear in the solution, on cooling. Slackening of the mixture. Indicates presence of a non-volatile organic acid. Odour of burnt sugar ; evolution of carbonic oxide which burns with blue flame. Oxalate. Cyanide Ferricyanide. Ferrocyanide. S phocyanide. Sulphite. Hypos phite (or from < oxidation of sulpl ric acid). Chloride, (except Hg, Ag, Pb a Sn.) Sulphide. Acetate. Bromide. Iodide. Chlorate. Nitrate. Chromate. Fluoride. Borate. Tartrate. Citrate Tannate. Galla Tartrate. * It is intended that the evidence furnished by the results of Exp. III. should be followed up by employing these confirmatory tests. 83 PREPARATION OF THE SOLUTION WHICH IS TO BE EXAMINED FOE- ACID RADICALS. Hydrochloric acid. If, on examining for basic radicals, the original solution was acid or neutral, and CARBONIC ACID was detected (by effervescence and reaction with hydrate of calcium), boil the solution to be pre- pared (a similar one to that used in the analysis for basic radicals) with hydrochloric acid, in order to expel all carbonic acid, If carbonic acid was not detected, this step may be omitted. If the original solution was alkaline, the addition of hydrochloric acid might indicate the probable presence of one or more of the following acids, if present : CARBONIC ACID, HYDROSULPHUMC ACID, HYDROCYANIC ACID, Silicic acid, Hyposulphurous acid, Hydroferrocyanic acid, Benzoic acid. If Silver, Lead, or Mercury were present in the original solution, these will be here precipitated by hydrochloric acid, and must be removed by nitration. Hydrosulphuric acid. Through the remaining part of the solution pass hydrosulphuric acid gas. The following, if present, will be decomposed and their presence rendered more or less evident : SULPHUROUS ACID (in an acid solution), IODIC ACID (reduced to iodide), page 64. The presence of Tin, Antimony, Arsenic, and Chromium, as acid radicals, would be revealed by the action of hydrosulphuric acid, when testing for basic radicals. Remove, by nitration, any bodies precipitated by hydrosulphuric acid. Sulphide of Ammonium. If any members of Groups III. and IV. (Basic radicals) were detected during the examination for basic radicals, precipitate them by sulphide of ammonium and remove. Carbonate of Sodium. % After boiling well, to expel all hydrosulphuric acid, add to the solution carbonate of sodium in some quantity. All basic radicals, except Potassium, Sodium, and Ammonium, will thus be precipitated and must be removed. Hydrate of Potassium. If Ammonium has been detected in the previous analysis, boil the filtrate from the carbonate of sodium precipitate, with hydrate of potassium, until no ammonia is evolved. Test the solution, thus prepared, with test-paper. Render it neutral by hydrate of ammonium or by nitric acid, as may be required, taking care to exercise extreme delicacy in bringing it into this condition. The prepared solution may now be examined for acid radicals, according to the plan detailed in the following pages. 11 84 BEHAVIOUR OF ACID RADICALS ANI Chloride of Barium in a neutral solution. Nitrate of Silver in an acidified solution. Group I. Sect. I. Sulphuric acid . . I. Hydrofluosilicic acid * . 2. Sect. II. Carbonic acid , . 3. Silicic . . 4. [Hydrosulphuric ,, ] Sect. III. Phosphoric acid . .5. Boracic . .6. Oxalic ,, . 7. Hydrofluoric,, . . 8. Sect. IV. _ Chromic acid . . 9. Sulphurous acid . .10. Hyposulphurous acid . n. lodic .12. [Arsenious and arsenic acids] 13. i. Sulphate, white . ) . . 2. Fluosilicate,white.i msoLmHC1 3. Carbonate, white . 1 sol. in HC1. with 4. Silicate, white. ( decomposition. 5- Phosphate, white . [sol. in HC1. 6. B OF ate, white . 1 without 7- Oxalate, white . | decomposi- 8. Fluoride, white. ( ^u. g. Chromate, pale-yellow . [acid solution 10. Sulphite, white . J decomposed ii. Hyposulphite, white . jby hydrosul- 12. lodate, white . [ phuric acid. 4. White, from a neutral solution. 5. Yellow, from a neutral solution. 6. White, 7. White, 9. Crimson, from a neutral solution. 13. (See Tables for Basic radicals.) Group II. Sect. I. Hydrochloric acid . . i. Hydrobromic . .2. Hydrocyanic . .3. Hydroferricyanic acid . 4. Sect. II. Hydriodic acid . 5. Hydrosulphuric acid . 6. Hydroferrocyanic acid , 7. Hydrosulphocyanic 8. ' - i. Chloride, a. white [ so i in 2. Bromide, a. white-yellow ) hydrate 3. Cyanide, a. white j of am- 4. Ferricyanide, a- orange [monium 5- Iodide, a. pale-yellow H ns ol..in 6. Sulphide, . black 1 hydrate 7. Ferrocyanide, . white f Jf am- 8. Sulphocyanide, jmonium. Group III. Nitric acid. Chloric Not precipitated. Not precipitated. ORGANIC ACIDS. i. Tartrate, white. 2. Citrate, white. i. White, from a neutral solution. 2. White, Group I. Tartaric acid . i. Citric . i. Group II. Succinic acid . . i, Benzoic . . 2. Tannic . 3. Gallic . 4. 3. Tannate, white. 4. Gallate, white (only partially). - Group III. Acetic acid . . . i. Uric . .2. 2. Urate. a Also precipitated by nitrate of silver from a neutral solution. 85 THEIR SALTS WITH GENERAL REAGENTS. Chloride of Calcium. Ferric Chloride in a neutral solution. set free with effervescence by Hydrochloric acid. Decomposed by Hydrosulphuric acid in an acid solution. i 3. Ppt. with CaHO. 5. Phosphate, <* white (sol. in ace- 6. Borate, . white | tic acid. 7- Oxalate, a. white ( insol. in 8. Fluoride, <*. white ( acetic acid. 5. White. 9. ( Green solution with ( separation of sulphur, i o. Separation of sulphur. * ' \i. Reduction to Iodide. 13. (See Basic radicals) a. 3. Odour. 4. Coloration, green. 7. Blue. 8. Coloration, deep-red. 6. ( Blackens paper < moistened with ( acetate of lead. Not precipitated. Not precipitated. i. Tartrate, white, sol in KHO. i- Citrate, /? white, insol. in KHO. i. SuCCinate, red-brown. 2. Benzoate, buff. 3- Grallate, bluish-black. 4- Tannate, bluish-black. i. Coloration, deep red. o These are precipitated from a neutral solution. /3 Only precipitated on boiling. a These acids are converted by HaS into their correspond- ing sulphur acids, and are detected and separated in the process for basic radicals. 112 86 METHOD OF ANALYSIS FOR GROUP I. (INORGANIC AND ORGANIC ACIDS.) CHLORIDE OF BARIUM precipitates from a neutral solution, Sulphuric acid, Phosphoric acid, Boracic acid, Hydrofluosilicic acid, Oxalic acid, Tartaric acid, (Silicic acid), Hydrofluoric acid, Citric acid. The other members of this Group {page 42) will, if present, have been detected during the course of analysis for basic radicals, or during the preparation of the solution before examining for acid radicals. SILICIC ACID will be precipitated, if not previously detected and removed. Care must be exercised to have the solution perfectly neutral before adding chloride of barium, If the solution was originally alkaline, it is most effectually rendered neutral by evaporating until the solution shews no alkaline reaction with litmus-paper. If acid, hydrate of ammonium is employed to neutralize. BOEATE of Barium, TARTRATE of Barium, and CITRATE of Barium are soluble in salts of ammo- nium. If the solution, previously acid, has been neutralized by hydrate of ammonium, the non-formation of a precipitate with chloride of barium will not indicate positively the absence of Boracic acid, Tartaric acid, or Citric acid, in consequence of the possible formation of chloride of ammonium. If chloride of barium produces a precipitate, the presence of SULPHURIC ACID, HYDROFLUOSILICIC ACID, or PHOSPHORIC ACID, can only be inferred with any certainty. If chloride of barium fails to produce a precipitate, the absence of SULPHURIC ACID, HYDRO- FLUOSILICIC ACID, PHOSPHORIC ACID, OXALIC ACID, or HYDROFLUORIC ACID, can only be certainly inferred. ANALYSIS OF PRECIPITATE PRODUCED BY CHLORIDE OF BARIUM IN A NEUTRAL SOLUTION. The precipitate is collected, washed, treated with hydrochloric acid in slight excess, and boiled gently. Sulphate of barium and Fluosilicate of barium are insoluble in hydro- chloric acid ; the barium salts of the other acid radicals are soluble in this acid. The insoluble residue may be rendered soluble in water by fusion with carbonate of sodium and nitrate of potassium. Acetic acid is added to the aqueous solution, and then chloride of calcium. Sulphuric Sulphate of calcium is insoluble, but Fluosilicate of calcium is soluble, acid. in acetic acid. This insolubility indicates the presence of the Sulphuric radical. HydroflllO- The presence or absence of the Fluosilicic radical in the acetic acid solu- S111C1C aClu. tion may be determined by the " etching test " (page 44, III.). The solution is neutral. Add BaCl. r Filter. Wash ppt. Add HC1 to ppt. Boil gently. 2 Filter. (Examine filtrate as on next page.) Residue from 2. Fuse with Na ? C0 3 + KN0 3 . Digest with H 2 0. Add HC 2 H 3 2 . Add CaCl. 3 Filter. Insoluble residue indicates presence of Sulphuric acid. Filtrate from 3. Heat with conc d . H 2 S0 4 . Dense fumes which etch glass indicate the presence of Hydrofluosilicic acid. 87 METHOD OF ANALYSIS FOR GROUP I. (CONTINUED). The filtered hydrochloric acid solution is treated with hydrate of ammo- nium. Phosphate, Oxalate, and Fluoride of barium may be re-precipitated. Borate, Oxalate, Fluoride, Tartrate and Citrate of barium, and possibly Silicate of barium, may be contained in the solution. (If no re-precipitation occurs, the absence of Phosphoric acid can alone be affirmed with any certainty.) The precipitate is re-dissolved in hydrochloric acid, boiled with carbonate of sodium, to convert into sodium salts (if necessary filtering from any pre- cipitate of carbonate of barium), and re-precipitated as calcium salts by adding chloride of calcium. Phosphate of calcium is soluble in acetic acid. After adding acetic acid the solution may be tested for the Phosphoric radical by ferric chloride or molybdate of ammonium (page 46). Oxalate or Fluoride of calcium may be thrown down along with the Phosphate. They are insoluble in acetic acid. One portion of the insoluble residue may be tested for Fluorine by con- centrated sulphuric acid (page 47). Another portion, for the Oxalic radical, by concentrated sulphuric acid and binoxide of manganese (page 47). The filtrate from the hydrate of ammonium precipitate, or the solution in which that reagent has failed to produce a precipitate, may contain Boracic acid, Oxalic acid, Hydrofluoric acid, Tartaric acid, Citric acid, or Silicic acid. The solution is divided into two portions. ( Silicic acid.) A. This portion is evaporated to dryness, treated with hydrochloric acid and water, and again evaporated, in order to convert any Silicic acid into insoluble silicic anhydride. The solution which remains after this operation is divided into three portions. Phosphoric acid. Oxalic acid. Hydro- fluoric acid. Filtrate from 2, preceding page. Add NH 4 HO. ...Filter. Boracic acid. Hydro- fluoric acid. Oxalic acid. Citric acid. Tartaric acid. a. Test for the Boracic radical with turmeric paper (page 46, note a). b. Test for Fluorine, by means of concentrated sulphuric acid and sand, or by the " etching test" (page 47). c. Test for Oxalic acid, with concentrated sulphuric acid, and binoxide of manganese (page 47). B. This portion of the solution is treated with a small quantity of hydrate of potassium, in order to decompose any chloride of ammonium which may -have been formed (page 55, notes a). Chloride of calcium is then added, and the whole boiled. After allowing to cool, more hydrate of potassium is added. A precipitate indicates the presence of the Citric radi- cal, since citrate of calcium is insoluble, whilst Tartrate of calcium is soluble in hydrate of potassium. Test the filtered solution for the Tartaric radical, with a crystal of nitrate of silver (page 55, note a). Residue from i. Dissolve in HC1. Boil with Na 2 C0 3 . (Filter from any ppt.) Add CaCl. Add HC 2 H 3 2 . 2 Filter. Add Fe 2 Cl 3 to filtrate. White-yellow ppt. =(Fe 2 ) 3 P0 4 ? or test with Molyb. Am. Residue from 2. Divide into two portions. A. Heat with conc d . H 2 SO 4 . Dense fumes =HF. Fumes etch glass. B. Heat with conc d . Effervescence indicates presence of Oxalic acid. Filtrate from i, or solution after adding NH 4 HO. Divide into two portions. A. Evaporate to dryness. Add HCl and H 2 O. Evaporate again. 3 Filter. Residue = Si 2 3 . Divide solution from 3, into three portions. a. Test with turmeric paper. Red coloration indicates presence of Boracic acid. b. Heat with conc d . H 2 S0 4 + sand. (p. 47, VI. ii.) Deposit of Silica indicates presence of Hydrofluoric acid. c. Heat with conc d . H 2 SO 4 + Mn 2 O 2 . Effervescence indicates presence of Oxalic acid. B. Add a little KHO. Add CaCl. Boil. When cool, add KHO. White ppt. = CagCaHsOy. Citric acid. 4 Filter. Add NH 4 HO to filtrate. Add crystal of AgN0 3 . Heat gently. Metallic silver indicates presence of Tartaric acid. METHOD OF ANALYSIS FOR GROUP II. NITRATE OF SILVER precipitates from an acid solution (acidified with nitric acid), Hydrochloric acid, Hydriodic acid, Hydrobromic acid, Hydroferrocyanic acid, Hydroferricyanic acid, Hydrosulphocyanic acid, Hydrocyanic acid. Nitrate of silver also precipitates many other acid radicals, if the solution is not decidedly acid. If the addition of nitric acid before nitrate of silver produces any precipitate, this will be due to the presence of certain acid radicals of the first Group. The precipitate may be filtered off and neglected. ANALYSIS OF PRECIPITATE PRODUCED BY NITRATE OF SILVER IN AN ACID SOLUTION. The precipitate is treated with dilute nitric acid, to ensure the removal of all acids except those belonging to this group. After filtering, the preci- pitate is treated with hydrate of ammonium and heated. This operation serves to separate the group into two sections. The residue may contain Hydriodic acid, Hydroferrocyanic acid, or Hy- drosulphocyanic acid. The solution may contain Hydrochloric acid, Hydrobromic acid, and pos- sibly Hydrocyanic acid. A portion of the residue is heated with concentrated nitric acid. Hy- driodic acid will manifest its presence by the violet vapours of iodine which accompany the decomposition. [If Hydriodic acid is detected, it will be necessary to test a portion of the original solution with a view to determine whether iodine existed in the form of iodide or iodate. They are distinguished by the difference in the reactions with concentrated sulphuric acid, since an iodate does not evolve free iodine when heated with this acid (pages 49 and 50).] Hydrosulphocyanic acid yields a yellow precipitate when heated with concentrated nitric acid. The remaining portion of the residue is boiled with hydrate or carbonate Cyanic acid, of potassium or sodium, to convert any ferrocyanogen into soluble ferro- cyanide of potassium or sodium. The radical may then be sought for according to the plan given in note 7, page 53, or with ferric chloride (in the latter case previously adding some hydrochloric acid). acld. (lodic acid ) Hydrosul- phocyanic acid. The solution is rendered acid, by adding HN0 3 . (Filter any ppt. and neglect it.) Add AgNOs. r Filter. Residue from i. Add dilute HN0 3 . 2 Filter. Add NHJ10 to ppl. 3 Filter. (Examine nitrate as on next page. Divide residue into two portions. A. Heat with conc d . HN0 3 Violet vapours = I. (Examine original solution for Hydriodic and lodic acid.) Yellow ppt. indicates presence of Hydrosulphocyanic acid. B. Add KHO or NaHO or K 2 C0 3 or Na C0 3 . Boil. Add to solution HC1. Add Fe 2 Cl 3 . Blue ppt. = (Fe 2 ) 2 (Cfy) 3 or test as in note 7, page 53 for Hydroferrocyanic acid. 89 Hydrobro- mic acid. Hydrochlo- ric acid. Hydrocy- anic acid. Hydroferri- cyanic acid. METHOD OF ANALYSIS FOE GKOUP II. (CONTINUED). The solution (after adding hydrate of ammonium to the nitrate of silver precipitate) may contain Hydrochloric acid, Hydrobromic acid, and possibly Hydrocyanic acid. (Hydrocyanic acid will probably have been converted into a sulphocy- auide, and ferricyanogen into ferrocyanogen by the action of hydrosulphuric acid, in preparing the solution.) The solution is treated with excess of nitric acid to re-precipitate as sil- ver salts. The precipitate (after washing by decantation) is ignited in a crucible, in order to decompose the Cyanogen compounds of silver, the silver being thereby reduced to the metallic state. The odour during this operation will probably lead to the detection of Cyanogen, if it is present. The fused mass is treated with boiling dilute nitric acid. The solution will contain nitrate of silver, and if now hydrochloric acid is added, a precipitate will indicate the previous presence of Hydrocyanic acid or Hydroferricyanic acid. Any residue, after fusion, may contain the radicals Chlorine or Bromine. This residue is fused again with carbonate of potassium and sodium, and dissolved in water. One portion is treated for Bromine by means of sulphuric acid and starch-paste (p. 50, IV. i.). // Bromine is present, another portion is tested for Chlorine, with sul- phuric acid and chromate of potassium (p. 50, IV. ii.). If this latter course becomes necessary, it will however be advisable to operate with a portion of the original solution. // Bromine is absent, the residue can only contain Chlorine, and further examination becomes unnecessary. A special examination of a portion of the original solution must be undertaken, if the presence of Hydrocyanic acid on Hydroferricyanic acid is suspected. The former may be detected by the reactions with sulphide of ammonium (p. 51); the latter by the negative results when testing for Hydrocyanic acid with sulphide of ammonium, and the reactions on subse- quently adding ferrous sulphate. Filtrate from 3, preceding paye. Add excess of HN0 3 . r Filter. Wash ppt. by decantation. Ignite the ppt. (Observe if any odour.) Add to fused mass HN0 3 . 2 Filter. Add HC1 to filtrate. < White ppt. = AgCl indicating presence of Cyanide or Ferricyanide of silver in previous ppt. Residue from i. Fuse with Na 2 C0 3 + K 2 C0 3 . Dissolve in H 2 0. Divide into two portions. A. Add conc d . H 2 SO 4 and some starch-paste. Heat. Starch-paste coloured yellow indicates presence of Bromine. B. If Bromine is present. Evaporate (or portion of the original solution) to dryness. Heat with conc d . H^S0 4 + KCrO 2 . Condense vapours. Add NH 4 HO to liquid. Yellow colour indicates presence of Chlorine. Acetic acid gives a crimson ppt, with this yellow solution. Examine specially for Hydrocyanic acid and Hydroferricyanic acid in original solution. Test as in page 51, III. for Hydrocyanic acid. Test as in p. 50, II. for Hydroferricyanic acid. 90 METHOD OF ANALYSIS FOR GROUP III. Nitric acid, and Chloric acid, are not precipitated by the reagents employed to precipitate the former groups. SULFHINDIGOTIC ACID produces a yellow colour in a solution which contains one or both of these acids. Nitric acid. If this coloration with a solution of indigo has taken place, the presence of Nitric acid is revealed by the characteristic reactions with ferrous sulphate in presence of sulphuric acid (p. 54, I.). Chloric Chloric acid is identified by the decomposition effected by sulphurous acid, and the subsequent reaction acid. w ith nitrate of silver (p. 54, IV.). METHOD OF ANALYSIS FOR GROUP II. (ORGANIC ACIDS.) / FERRIC CHLORIDE precipitates from a neutral solution, ar*\f\ A \\- I -^enzoate ^ "" on dissolves in hydrochloric acid, with separation of crystalline Benzoic acid. iMpWUVMIV V* 11 Benzoic acic Distinguished Gallic acid, ) . > bluish-black, -j Distinguished by reactions with ferric chloride, or solution of gelatine (p. 57). Acetic acid 1 f Colour disappears, if Acetic acid only is present, on adding mer- ' I Distinguished also by reactions with chloride of barium and alcohol (p. 56). Gallic acid, Tannic acid produces coloration in a solution in presence of / Colour disappears, if Acetic aci I deep red colour. < curie chloride, or on boiling. Hydrosulphocyamc acid, I I m , . . ,. ........ .-, , , , , , * lest also for Acetic acid with sulphuric acid and alcohol (p. 58). Hydroferricyanic acid. green tint. [Phosphoric acid (white) and Hydroferrocyanic acid (blue) may also be precipitated from a neutral solution by ferric chloride]. ACIDS WHICH ARE DETECTED DURING THE ANALYSIS FOR BASIC RADICALS, OR DURING THE PREPARATION OF THE SOLUTION TO BE EXAMINED FOR ACID RADICALS. Carbonic Acid, j are detected by the effervescence, on adding the group-reagent, hydrochloric acid. The HydroSUlphuriC Acid, / characteristic reactions by which they are identified, are given on p. 85. They are Hydrocyanic Acid, J invariably detected when examining for basic radicals (p. 64). (are decomposed, with separation of sulphur, by hydrosulphuric acid, if hydrochloric acid is present. Hydrochloric acid causes a deposit of sulphur in the case of Hypo- sulphurous acid, but not in the case of Sulphurous acid. The latter is detected in the preliminary examination (p. 82). APPENDIX. 12 92 ANALYSIS OF SUBSTANCES, INSOLUBLE IN WATER AND IN ACIDS. (FRESENIUS.) All, otherwise insoluble, bodies which come under the student's notice, in an elementary course, will, after fusion with alkaline carbonate (page 21, par. 8), yield to the solvent ^action of water, hydrochloric acid, or nitric acid. The following method, adapted from Fresenius, indicates the mode of dealing with such bodies in the course of actual analysis. The substances to which this method is applicable are the following : BARIUM, STRONTIUM, LEAD, as Sulphates. SILVER, as Chloride, Iodide, Bromide, and Cyanide. LEAD, as Chloride. CALCIUM, as Fluoride (and certain other Fluorides). SILICATES. ALUMINIUM, chiefly as Sesquioxide. CHROMIUM, as Sesquioxide. Certain Salts of TIN, ANTIMONY, and ARSENIC. (Sulphur and Carbonaceous matter.) TREATMENT OF INSOLUBLE SUBSTANCES, AFTER MAKING A PRELIMINARY EXAMINATION OF THE SUBSTANCE UNDER ANALYSIS. Heat for some time with acetate of ammonium (conc d ). Solution. Residue. Divide into three parts. Digest with KCy and water. i. ii. iii. Test for Test for Test for Residue. Solution. Cl. H 2 SO 4 . Pb. Expel Sulphur, if present, Add (NH 4 ) 2 S. by fusion. Ppt. =AgS. Fuse residue with Dissolve in HNO 3 . i part KNO a ) Dilute with H 2 0. 1 parts K 2 CO a \. Add HC1. 2 parts 2Va 2 <70 3 ) White ppt. = AgCl. Treat with H 2 O. (See next page, whether silver Boil. is combined with Cl, I, Br or Cy.) Filter. Residue Solution. Wash thoroughly, (Contains acids, and such basic radicals (add first washings to filtrate) as are soluble in alkalis.) until no ppt. is formed by Bad "Yellow colour in the filtrate indicates the in the washings. presence of Chromic acid. Dissolve in HC1. Test for it by means of acetic acid and (Effervescence indicates alkaline earths.) acetate of lead. Test for Basic Radicals, Divide remaining portion into 4 parts, as in Group II. p. 70. 1 i. Test for H2S04 r ii. Test for Fluorine with H 2 S0 4 (etching test.) 1 n iii. iv. Test for Arsenic Acidify with HC1. with H 2 S, and for Evaporate to dryness. HaPO* Add HC1 and H 2 0. with Molyb. Am. Evaporate again. Residue. Solution. Si,O :i . Test for basic Treat a portion as radicals on next page. which are soluble in alkalis (chiefly Sn, Sb, As.) 93 ANALYSIS OF INSOLUBLE SUBSTANCES (CONTINUED.) ANALYSIS OF ALKALINE SILICATES. The insoluble substance which may contain an alkali in combination with the silicic radical, is decomposed by fusion with four parts of hydrate of barium, for a considerable time at a high temperature. The fused mass is then treated as follows : Treat with hydrochloric acid and water, to dissolve. Treat the solution with hydrate and carbonate of ammonium, to precipitate the Barium. Filter. Evaporate filtrate to dryness. Ignite. Dissolve the residue in water. Precipitate again with hydrate and carbonate of ammonium. Filter. Evaporate to dryness. Ignite to expel ammonia. Test the residue for Potassium and Sodium in the usual manner. TO ASCERTAIN WHETHER THE INSOLUBLE SALT OF SILVER IS A CHLORIDE, IODIDE, BROMIDE, OR CYANIDE. Treat a portion of the original substance with water to remove soluble matter. And then with nitric acid for the same purpose. Wash the residue with water. Boil with rather dilute solution of hydrate of sodium. Filter, (i) Acidify the filtrate with nitric acid, and test for Ferrocyanogen and Ferricyanogen. (This may be effected by means of ferric chloride.) Digest the residue from (i) with granulated zinc and water. Add some dilute sulphuric acid. (The object of this is to reduce the silver to the metallic state.) Filter, in ten minutes. Add carbonate of sodium to filtrate, to precipitate zinc. Test filtrate specially for Chlorine, Bromine, Iodine, and Cyanogen. 94 ANALYSIS OF ALLOYS. The principle of analysis depends on the fact that nitric acid converts certain metals into nitrates, in which condition they are soluble, whilst nitric acid either fails to attack other metals, or merely oxidising them fails to reduce them to a soluble form. The alloy must be reduced to as complete a state of subdivision as is possible. Boil gently with tolerably concentrated nitric acid. Add a considerable quantity of water. Boil to remove excess of acid. Filter. Residue may contain GOLD ANTIMONY PLATINUM. TIN. (Small traces of Antimony may be completely dissolved by nitric acid. Small quantities of Platinum alloyed with Silver may also dissolve in nitric acid.) If the residue is white, metallic or a black mass, it probably contains it probably contains, TIN, or GOLD, or ANTIMONY. PLATINUM. The residue is well washed. Boil with nitro-hydrochloric acid, (three parts hydrochloric to one part of nitric acid). Solution. Analyse this, in the usual manner, for the metals. SILVEB. LEAD. MEBCUBY. ABSENIO. BISMUTH. COPPEB. IRON. ALUMINIUM. ZINC. COBALT. NICKEL. Residue will be a white insoluble powder. Consists of CHLOBDOE or SILVEB or possibly CHLOBIDB OP LEAD. Treat as a substance insoluble in water and acids, p. 94. Solution. Divide the solution into two parts, i. ii. Test for Test for GOLD and PLATINUM, ANTIMONY and TIN, as on p. 70. as on p. 72. HOME USE CIRCULATION DEPARTMENT MAIN LIBRARY This book is due on the last date stamped below. 1-month loans may be renewed by calling 642-3405. 6-month loans may be recharged by bringing books to Circulation Desk. Renewals and recharges may be made 4 days prior to due date. ALL BOOKS ARE SUBJECT TO RECALL 7 DAYS Hntn UHIC. untbntu uui. BECU Cier 'EPT APK o - 'M m 2 2 RECD Cine HFPT MAY LD21-A30m-7,'73 (B2275S10)476 A-32 General Library University of California Berkeley