The iron and copper separate as oxides, the solution contains sulphate, arsenate, and antimonate of potassa (Rivot, Beudant, and Daguin, "Compt. rend.," 1853, 835; "Journ. f. prakt. Chem.," 61, 133). c. ARSENIC AND ANTIMONY FROM COBALT AND NICKEL. Dilute the nitric acid solution with water, add a large excess of 157 potassa, heat gently, and conduct chlorine into the fluid until the precipitate is black. The solution contains the whole of the arsenic and antimony, the precipitate the nickel and cobalt, in form of sesquioxide (Rivot, Beudant and Daguin, "Compt. rend.,” 1853, 835; "Journ. f. prakt. Chem.," 61, 133). 8. Method based upon the Separation of Arsenic as Arsenate of ARSENIC ACID FROM THE ALKALIES, ALKALINE EARTHS, OXIDE Proceed exactly as in the separation of phosphoric acid by mercury 158 (§ 134, b, y). The arsenic acid cannot be determined in the insoluble residue in the way in which the phosphoric acid is determined. Treat the filtrate as directed § 135, 1 (H. Rose). 9. Method based upon the Separation of Arsenic as Arsenate of ARSENIC ACID FROM ALUMINA AND THE OXIDES OF GROUP IV. Proceed as directed § 135, f, a. Treat the precipitated arsenate 159 of magnesia and ammonia the same way as the precipitated phosphate of magnesia and ammonia (see § 135, f, a). 10. Method based upon the Separation of Arsenic as Arsenio- ARSENIC ACID FROM ALL OXIDES OF GROUPS I.-V. Separate the arsenic acid as directed in § 127, 2 b, and treat the 160 filtrate as directed in § 135, m. 11. Method based upon the Insolubility of Arsenate of Sesquioxide ARSENIC ACID FROM THE BASES OF GROUPS I. AND II., AND FROM Precipitate the arsenic acid, according to circumstances, as directed 161 § 127, 3, a or b, filter, and determine the bases in the filtrate. 12. Method based upon the Insolubility of Chloride of Silver. SILVER FROM GOLD. Treat the alloy with cold dilute nitrohydrochloric acid, dilute, and 162 filter the solution of the terchloride of gold from the undissolved chloride of silver. This method is applicable only if the alloy contains less than 15 per cent. of silver; for if it contains a larger proportion, the chloride of silver which forms protects the undecomposed part from the action of the acid. In the same way silver may be separated also from platinum. 13. Method based upon the Insolubility of certain Sulphates in Water or Spirit of Wine. ARSENIC ACID FROM BARYTA, STRONTIA, LIME, AND OXIDE OF LEAD. Proceed as for the separation of phosphoric acid from the same 163 oxides (§ 135, c). The compounds of these bases with arsenious acid are first converted into arsenates, before the sulphuric acid is added ; this conversion is effected by heating the hydrochloric acid solution with chlorate of potassa. 14. Method based upon the Separation of Copper as Subiodide. COPPER FROM ARSENIC AND ANTIMONY. Dissolve in nitric or sulphuric acid, taking care to add the acid 164 only slightly in excess, dilute with water or, in presence of antimony, with water containing tartaric acid, and precipitate the copper as in 113. Arsenic and antimony remain in solution (Flajolot). 15. Method based upon the Separation of Copper as Oxalate. COPPER FROM ARSENIC. Add to the nitric acid solution ammonia until the blue precipitate 165 formed remains undissolved upon further addition of the reagent, then effect solution by an excess of oxalate of ammonia. Add, cautiously, hydrochloric or nitric acid to acid reaction, and allow the mixture to stand. The copper separates almost completely as oxalate, which is then converted by ignition in the air into oxide. Add ammonia to the filtrate, and precipitate with a few drops of sulphide of ammonium the minute trace of copper still retained in solution (F. Field, "Chem. Gaz.," 1857, 313). 16. Method based upon the different deportment of the several GOLD FROM LEAD AND BISMUTH. These metals may be separated in solution by cyanide of potassium 166 in the same way in which the separation of mercury from lead and bismuth is effected (see 123). The solution of the double cyanide of gold and potassium is decomposed by boiling with hydrochloric acid, and, after expulsion of the hydrocyanic acid, the gold determined by one of the methods given in § 123. II. SEPARATION OF THE OXIDES OF THE SIXTH GROUP FROM EACH OTHER. $165. Index: Platinum from gold, 167 ;-from antimony, tin, and arsenic, 168. Gold from platinum, 167;-from antimony, tin, and arsenic, 168. Tin from gold and platinum, 168;-from arsenic, 169, 176, 177, 178;-from antimony, 171, 175, 177;—protoxide from binoxide of tin, 181. Antimony from gold and platinum, 168;-from arsenic, 170, 171, 172, 173;-from tin, 171, 175, 177;-teroxide of antimony from antimonic acid, 180, 182. Arsenic from gold and platinum, 168;-from tin, 169, 176, 177, 178;-from antimony, 170, 171, 172, 173;arsenious acid from arsenic acid, 174, 179, 182. 1. Method based upon the Precipitation of Platinum as Potassiobichloride of Platinum. PLATINUM FROM GOLD. Precipitate from the solution of the chlorides of the metals the 167 platinum as directed § 124, b, and determine the gold in the filtrate as directed § 123, b. 2. Method based upon the Volatility of the Chlorides of the inferior Metals. PLATINUM AND GOLD FROM TIN, ANTIMONY, AND ARSENIC. Heat the finely divided alloy or the sulphides in a stream of 168 chlorine gas. Gold and platinum are left, the chlorides of the other metals volatilize (compare 132, 133). 3. Methods based upon the Volatility of Arsenic and Tersulphide of Arsenic. a. ARSENIC FROM TIN (H. Rose). Convert into sulphides or into oxides, dry at 212° F., and heat a 169 weighed portion of the dried mass in a bulb-tube, gently at first, but gradually more strongly, conducting a stream of dry sulphuretted hydrogen gas through the tube during the operation. Sulphur and tersulphide of arsenic volatilize, sulphide of tin is left. The tersulphide of arsenic is received in a small flask connected with the bulb-tube, in the manner described in 132, which contains dilute solution of ammonia. When upon continued application of heat no further sign of sublimation is observed in the colder part of the tube, drive off the sublimate which has collected in the bulb, allow the tube to cool, and then cut it off above the coating. Divide the separated portion of the tube into pieces, and heat these with solution of soda until the sublimate is dissolved; unite the solution with the ammoniacal fluid in the receiver, add hydrochloric acid, then, without filtering, chlorate of potassa, and heat gently until the tersulphide of arsenic is completely dissolved. Filter from the sulphur, and determine the arsenic acid as directed § 127, 2. The quantity of tin cannot be calculated at once from the blackish-brown sulphide of tin in the bulb, since this contains more sulphur than corresponds to the formula Sn S. It is therefore weighed, and the tin determined in a weighed portion of it, by converting it into binoxide, which is effected by moistening with nitric acid, and ignition (§ 126, 1, c). Tin and arsenic in alloys are more conveniently converted into oxides by cautious treatment with nitric acid. If, however, it is wished to convert them into sulphides, this may readily be effected by heating 1 part of the finely divided alloy with 5 parts of carbonate of soda, and 5 parts of sulphur, in a covered porcelain crucible, until the mass is in a state of calm fusion. It is then allowed to cool, dissolved in water, the solution filtered from the sulphide of iron, &c., which may possibly have formed, and the filtrate precipitated with hydrochloric acid. b. ARSENIC FROM ANTIMONY IN ALLOYS. Heat a weighed portion of the finely divided alloy with 2 parts 170 of carbonate of soda and 2 parts of cyanide of potassium in a bulbtube, through which dry carbonic acid is transmitted; apply a gentle heat at first, but increase this gradually to a high degree of intensity, and continue heating until no more arsenic volatilizes. Take care not to inhale the escaping fumes; the safest way is to insert the hind part of the bulb-tube into a flask, in which the arsenic will sublime. Allow the bulb-tube to cool; after cooling, treat the contents, first with a mixture of equal parts of spirit of wine and water, then with water, and weigh the residuary antimony. The quantity of the arsenic is calculated from the loss. This method gives only approximate results. The direct fusion of the alloy in a stream of carbonic acid or hydrogen gas, without previous addition of carbonate of soda and cyanide of potassium, would give most inaccurate results, as a large quantity of antimony volatilizes under these circumstances. 4. Methods based upon the insolubility of Antimonate of Soda. a. ANTIMONY FROM TIN AND ARSENIC (H. Rose). of Oxidize a weighed sample of the finely divided substance, in a 171 porcelain crucible, with nitric acid of 14 specific gravity, adding the acid gradually. Dry the mass on the water-bath, transfer to a silver crucible, rinsing the last particles adhering to the porcelain into the silver crucible with solution of soda, dry again, add eight times the bulk of the mass of solid hydrate of soda, and fuse for some time. Allow the mass to cool, and then treat with hot water until the undissolved residue presents the appearance a fine powder; dilute with some water, and add alcohol of 0.83 sp. gr. in sufficient quantity to make the proportion of its volume to that of the water as 1 to 3. Allow the mixture to stand for 24 hours, with frequent stirring; then filter, transfer the last adhering particles from the crucible to the filter by rinsing with dilute spirit of wine (1 volume of alcohol to 3 volumes of water), and wash the undissolved residue on the filter, first with spirit of wine containing 1 volume of alcohol to 2 volumes of water, then with a mixture of equal volumes of alcohol and water, and finally with a mixture of 3 volumes of alcohol and 1 of water. Add to each of the alcoholic fluids used for washing a few drops of solution of carbonate of soda. Continue the washing until the color of a portion of the fluid running off remains unaltered upon being acidified with hydrochloric acid and mixed with sulphuretted hydrogen water. Rinse the antimonate of soda from the filter, wash the latter with a mixture of hydrochloric acid and tartaric acid, dissolve the antimonate in this mixture, precipitate with sulphuretted hydrogen, and determine the antimony as directed § 125, 1. To the filtrate, which contains the tin and arsenic, add hydrochloric acid, which produces a precipitate of arsenate of binoxide of tin; conduct now into the unfiltered fluid sulphuretted hydrogen for some time, allow the mixture to stand at rest until the odor of that gas has almost completely gone off, and then separate the weighed sulphides of the metals as in 169. If the substance contains only antimony and arsenic, the alcoholic filtrate is heated, with repeated addition of water, until the fluid scarcely retains the odor of alcohol; hydrochloric acid is then added, and the arsenic determined as arsenate of magnesia and ammonia (§ 127, 2). b. DETERMINATION OF THE SULPHIDE OF ARSENIC CONTAINED IN THE COMMERCIAL SULPHIDE OF ANTIMONY (Wackenroder). Deflagrate 20 grammes of the finely pulverized sulphide of anti- 172 mony with 40 grammes of nitrate of potassa and 20 grammes of carbonate of soda, by projecting the mixture gradually into a redhot hessian crucible; treat the strongly ignited mass repeatedly with water, filter the solution, acidify the filtrate with hydrochloric acid, treat with sulphurous acid, and precipitate the arsenic with sulphuretted hydrogen. Digest the moist precipitate, which contains a small admixture of antimony, with carbonate of ammonia, filter, acidify the filtrate, conduct sulphuretted hydrogen into the fluid, and determine the arsenic as tersulphide as directed § 127, 4. 5. Methods based upon the Precipitation of Arsenic as Arsenate a. ARSENIC FROM ANTIMONY. Oxidize the metals or sulphides with nitrohydrochloric acid or 173 hydrochloric acid and chlorate of potassa, or with chlorine in alkaline solution (see § 148, II., 2, b); add tartaric acid, a large quantity of chloride of ammonium, and then ammonia in excess. Should the addition of the latter reagent produce a precipitate, this is a proof that an insufficient quantity of chloride of ammonium or of tartaric acid has been used, which error must be corrected before proceeding with the analysis. Then precipitate the arsenic acid as directed § 127, 2, and determine the antimony in the filtrate as directed § 125, 1. As basic tartrate of magnesia might precipitate with the arsenate of magnesia and ammonia, the precipitate should always, after slight washing, be redissolved in hydrochloric acid, and the solution precipitated again with ammonia. b. ARSENIOUS ACID FROM ARSENIC ACID. Mix the solution with a large quantity of chloride of ammonium, 174 precipitate the arsenic acid as directed § 127, 2, and determine the arsenious acid in the filtrate by precipitation with sulphuretted hydrogen (§ 127, 4). 6. Methods based upon the Precipitation of the Metals in the metallic state. a. TIN FROM ANTIMONY (Gay-Lussac). Heat a weighed portion of the finely divided alloy (or other form 175 of combination) with hydrochloric acid, add chlorate of potassa in small portions until the mass is dissolved, and then divide the fluid into two equal parts, a and b. In a precipitate both metals on a tin rod, rinse them off, and weigh; add to b a tolerably large |