785 



CHEMICAL ANALYSIS. 



CHEMICAL ANALYSIS. 



780 



the metallic state by heat in the presence of carbon, or from solutions 

 by metallic zinc. 



Silver is reduced from all its compounds at a red heat by alkaline 

 carbonates. 



Gold forms a purple precipitate with stanni-stannous chloride. 



Platinum in acid solutions forms a yellow precipitate with soluble 

 salts of ammonia and potash. 



Tin, see Gold. Tin is reduced from most of its compounds by red- 

 hot charcoal. 



* > The soluble compounds are decomposed by nascent 



hydrogen, and Ihe reduced metal forms with it antimonuretted and 

 arsenuretted hydrogen, which are inflammable gases. Arseuuretted 

 hydrogen reduces salts of silver. Metallic arsenic in a fine state of 

 division is soluble in chloride of lime. Arsenious acid forms a yellow 

 precipitate in ammonio-nitrate of silver, and a green one in ammonio- 

 sulphate of copper. It is precipitated as a metal by metallic copper. 

 The sulphide of antimony is converted into a volatile chloride by dry 

 hydrochloric acid. 



Aluminium. The oxide of aluminium, when heated with a salt of 

 cobalt, becomes of a bright blue colour. 



Chromium. The teroxide of chromium, or chromic acid, forms 

 characteristically coloured salts (chromates), with various metallic 

 bases. The sesquioxide and its salts are converted into chromate of 

 potash by fusion with nitrate of potash. 



Iron. The sesqui-salts of iron give a blood red colour with sulpho- 

 cyanide of potassium, and a blue precipitate with ferrocyanide of 

 potassium. The proto-salts are turned brown with nitric acid, and 

 give a blue precipitate with ferricyanide of potassium. 



ifanganete. The sulphide of manganese is flesh-coloured. All com- 

 pounds of manganese are converted into the bluish-green manganate of 

 soda, on fusion with a mixture of carbonate of soda and nitrate of 

 potash. 



Cobalt imparts an intense blue colour to a bead of borax in the blow- 

 pipe flame. 



Nickel. The oxide of this metal dissolves in ammonia with a blue 

 colour. 



Zinc is reduced to the metallic state by red-hot charcoal. The metal 

 in volatile and easily oxidisable ; its sulphide is white. Its oxide is 

 yellow whilst hot, but white when cold. 



Maynetia, when heated with nitrate of cobalt in the blowpipe flame, 

 becomes flesh-coloured. 



Lime forms an oxalate, insoluble in alkaline solutions and in acetic 

 acid. It gives a red colour to the blowpipe flame. 



Slrontia. Its chloride imparts a crimson colour to the flame of 

 alcohol. 



Baryta forms a sulphate insoluble in water, alkalies, and acids. 



For the special blowpipe reactions of the metallic bases, see 

 BLOWPIPE. 



The method of qualitative analysis thus briefly sketched, will be 

 better understood by supposing we have to examine a solution con- 

 taining a member of each group, under the supposition that we are, at 

 the commencement, ignorant as to what it contains. 



Let the solution contain, 



K, Sr, Mg, Al, Mn. Sn, Ag, HgO, Hi. ' 



A portion of the solution is heated with caustic potash, no ammonia 

 is evolved, therefore ammonia is absent. 



To the remainder an excess of hydrochloric acid is added, a white 

 precipitate (A) is formed. 



The filtrate from A is saturated with hydrosulphic acid, a brown- 

 black precipitate (B) is formed. 



The filtrate from B is boiled alone, and then with nitric acid, chlo- 

 ride of ammonium is added, and then ammonia. A white precipitate 

 (C) is formed. 



To the filtrate from C, sulphide of ammonium is added, a flesh- 

 coloured precipitate (D) is formed. 



The filtrate from D is boiled with carbonate of ammonia, a white 

 precipitate (E) is formed. 



To a portion of the filtrate from E phosphate of soda is added, a 

 white precipitate is formed. To the remainder arseniate of ammonia 

 ia added, a white precipitate (F) is formed. 



The nitrate from F is evaporated to dryness, ignited and dissolved in 

 water, giving solution Q. 



The separation of the metals into the groups has, therefore, been 

 effected ; the separation of the different members of the groups now 

 follows. 



The precipitate A is washed with boiling water on the filter. Sul- 

 phuric acid gives no precipitate in the filtrate, therefore lead is absent. 

 Ammonia added to A does not blacken it, therefore suboxide of mer- 

 cury is absent, but dissolves it, therefore silver is present. (Confirma- 

 tory : hydrochloric added to the ammoniacal solution, rcprecipitates 

 the silver as chloride ; this is reduced to the metallic state on charcoal ; 

 dissolved in nitric acid, neutralised with ammonia, and the character- 

 istic chromate and iodide of silver found on the addition of soluble 

 chroniate* and i>nliili--i.) 



The precipitate B is digested with sulphide of ammonium, it is 

 filtered and hydrochloric acid added to the filtrate throws down a 



ABTS AHD SCI. DIV. TOt. IL 



brown precipitate (G). The part of B insoluble in sulphide of ammo- 

 nium is digested with nitric acid ; a black residue remains, showing 

 the presence of protoxide of mercury. (Confirmatory : the Black 

 insoluble mass is dried, mixed with carbonate of soda, and heated in a 

 dry tube ; metallic mercury volatilises and condenses on the cold part 

 of the tube.) The filtrate from the sulphide of mercury is treated 

 with an excess of ammonia, a white precipitate is formed, showing the 

 presence of bismuth. (Confirmatory : the precipitate is separated by 

 filtration, dissolved in nitric acid, and dropped into water, a white 

 precipitate is formed. On adding carbonate of ammonia to the filtrate 

 from the bismuth, no precipitate is formed, therefore cadmium is 

 absent, on boiling the same solution with caustic potash no precipitate 

 is formed, therefore copper is absent.) 



The precipitate got by adding hydrochloric acid to the portion of B 

 dissolved in sulphide of ammonium is digested with carbonate of 

 ammonia and filtered, hydrochloric acid produces no precipitate in the 

 filtrate, therefore arsenic is absent. That which has not been dissolved 

 in carbonate of ammonia, is heated to redness with nitrate of amm'ouia, 

 then digested with tartaric acid and filtered : hydrosulphuric acid throws 

 down no sulphide from the filtrate, therefore antimony is absent. That 

 which has not been dissolved in tartaric acid, is boiled in nitro- 

 hydrochlorie acid and filtered. Neither chloride of ammonium, nor 

 protochloride of tin affect the filtrate, therefore platinum and gold are 

 absent. That which has not been dissolved in nitro-hydrochloric acid 

 is fused on charcoal with carbonate of soda : on scraping the fused 

 mass into a mortar and washing with water, a malleable metallic 

 globule is found, which shows the presence of tin. (Confirmatory : the 

 globule is boiled with hydrochloric acid ; on adding chloride of gold a 

 purple colour is formed.) 



The precipitate C is dissolved in hydrochloric acid ; cold caustic 

 potash produces a precipitate which dissolves in excess, therefore iron 

 is absent : on boiling the caustic potash solution, no precipitate is 

 formed, therefore chromium is absent j on adding an excess of hydro- 

 chloric acid and then an excess of ammonia, a white precipitate is 

 formed, therefore aluminium is present. (Confirmatory : the precipi- 

 tate is collected on a filter, dried and heated before the blowpipe with 

 a solution of cobalt ; a blue colour is produced.) 



The precipitate D is dissolved in nitro-hydrochloric acid, and then 

 boiled with an excess of carbonate of ammonia, a white precipitate 

 is formed, therefore manganese is present; (Confirmatory : a part of 

 the so-formed carbonate of manganese is fused with nitrate of potash 

 and carbonate of soda, a bluish-green mass is obtained of manganate 

 of soda ; another portion of the manganese precipitate is fused in the 

 outer blowpipe flame with borax, an amethyst bead is formed.) The 

 filtrate from the manganese is boiled with an excess of caustic potash, 

 no precipitate is formed, therefore nickel and cobalt are absent : sul- 

 phide of ammonium added to the caustic potash solution gives no 

 precipitate, therefore zinc is absent. 



The precipitate E is dissolved in hydrochloric acid, made alkaline by 

 ammonia, and treated with chromate of potash, no precipitate is 

 formed, therefore barium is absent. Sulphate of potash is added, and 

 the liquid allowed to stand for some hours ; a precipitate is formed, 

 showing the presence of strontium. The filtrate from the strontium 

 precipitate is made alkaline with ammonia, and then treated with 

 oxalate of ammonia : no precipitate is formed, therefore lime is absent. 



The precipitate F requires no examination, its formation proves the 

 presence of magnesium. 



The filtrate from F is evaporated to dryness, and ignited to expel 

 the ammoniacal and arsenical salts ; when the residue is dissolved in a 

 little water, it gives a precipitate with tartaric acid and also with 

 bichloride of platinum, therefore potatrium is present. (Confirmatory : 

 a wire dipped into the solution and held in the flame turns it violet, 

 which shows also the absence of sodium.) 



When the constituents of a body are quite unknown, a preliminary 

 examination of it in the dry way often saves time by giving some 

 clue to the bodies which are present. Thus the easy fusibility of a 

 substance when heated on charcoal, generally points to the presence of 

 the fixed alkalies. If it be heated in a narrow tube closed at one end, 

 with carbonate of soda, ammonia and mercury, if present, are volatilised. 

 If cyanide of potassium is added arsenic is volatilised, and so on. 



If the body to be analysed is in the solid form it is examined as 

 follows : It is boiled with water ; if it dissolves completely, the 

 method given above is at once applied. If it is only partly soluble in 

 water, the insoluble part is boiled with hydrochloric acid and filtered ; 

 if anything remains insoluble in hydrochloric acid, it "is treated with 

 nitric acid, and should this leave anything undissolved, the residue is 

 boiled with nitro-hydrochloric acid. The four extracts so got from 

 the same quantity of the substance by these reagents are then mixed, 

 and if any precipitation ensues, it is examined for the metals in A. 

 Any substance which resists the action of all these reagents when 

 successively used, does so in consequence of its containing some acid 

 or non-metallic element. The method of analysing such bodies is best 

 considered after the description of the behaviour of the acids. 



Detection of acids. Just as a large number of the bases are chiefly 

 detected by the peculiarity of their behaviour towards certain acids or 

 salts containing them, so acids are in general detected by the pecu- 

 liarity of their behaviour towards certain bases or salts containing the 

 latter. Hence it frequently happens that an acid and a base are 



