hydrobromic. The solubilities of the salts of the several acids with nitron are given herewith: 100 c.c. of water, slightly acidulated with sulphuric acid, dis solves at 18°-22° approximately Procedure for the Determination of Nitric Acid as Nitron Nitrate. Enough of the sample is taken to furnish about 0.100 g. nitric acid and dissolved in 80-100 c.c. of water with the addition of 10 drops of dilute sulphuric acid. The solution is heated nearly to boiling and treated with 10-12 c.c. of nitron acetate solution, which is added all at one time. The beaker containing the solution and precipitate is kept surrounded by ice water for about two hours. The precipitate is then transferred to a Munroe crucible and drained as completely as possible from the pale yellow supernatant liquid. It is washed with 10 or 12 c.c. of ice water, added in small portions, and the precipitate drained well after each washing. The precipitate is dried at 110° to constant weight. It contains 16.53% of NO3. On account of the appreciable solubility of the nitrate, it is to be expected that results should be a little low. This is not the case, however, as Busch and Gutbier have proved. It is probable that the precipitate occludes a little nitron acetate and in this way the error caused by the amount left in solution is compensated. 230. Nitroso-ẞ-Naphthol. 7 Quoting Treadwell-Hall, p. 451 of reference cited in § 13 of this book. 8 The reagent is prepared by dissolving 10 gm. of nitron in 100 c.c. of 5 percent acetic acid. The solution usually has a reddish color, but can be kept for a long time in a dark-colored bottle without its undergoing any change. This reagent precipitates the following elements from solutions which are slightly acid: copper, palladium, iron and cobalt; these metals may be quantitatively separated from antimony, aluminum, chromium, manganese, nickel, zinc, zirconium, magnesium, calcium, barium and strontium. Probably the most important application of nitroso-ẞ-naphthol is the determination of small amounts of cobalt in the presence of large amounts of nickel; for the separation of these two elements it is preferable to have them in the form of their sulphates or chlorides in a solution which is acidulated with hydrochloric acid; to this is added a hot solution of nitroso-ẞ-naphthol in 50 percent acetic acid until all the cobalt is precipitated. 10 The brick-red precipitate is then washed with cold 4 molar hydrochloric acid, then with hot 4 molar hydrochloric acid, and finally with water. For small amounts of cobalt the precipitate may be ignited in air and weighed as C0304. 231. Ether Saturated with Hydrochloric Acid. As first shown by W. Skey," if a hydrochloric acid solution of ferric chloride is shaken up with ether and the mixture allowed to separate into two layers, the ether layer will contain more or less of the ferric chloride, depending upon the relative volumes of the ether and the water layers and upon the concentration of the hydrochloric acid in the ferric chloride solution. Rothe,12 however, was the first to apply this principle to the technical analysis of iron compounds, and the method is usually referred to as "Rothe's Ether Method." The most favorable concentration of hydrochloric acid is 6.0 molar; if much above or below this molarity, then the percentage of ferric chloride which passes into the ether layer is considerably diminished, as shown by the inves A résumé of these separations is given by Knorre, Zeit. angew. Chem. 17, 677 (1904). 10 The author found that several samples of nitroso-8-naphthol obtained on the market precipitated nickel as well as cobalt. He then prepared some nitroso-8-naphthol according to the original directions of C. E. Groves, J C. S. 45, 294 (1884), and dissolved same in 50 percent acetic acid. This preparation also precipitated nickel, but after standing several days at room temperature (18°-22°) a brown precipitate settled out; after this precipitate was filtered off, the solution no longer precipitated nickel. It would seem from this experience that nitroso-ẞ-naphthol is likely to be associated with some compound which arises in its synthesis and which precipitates nickel. It is accordingly recommended that a blank be run on every sample of nitroso-ẞ-naphthol to see whether it precipitates nickel or not. 11 Chem. News, 36, 48 (1880). 12 J. W. Rothe, Mitt. könig. tech. Ver. 10, 132 (1892); Chem. News, 66, 182 (1892); Stahl und Eisen, 12, 1052 (1892). % Iron in ether layer 20 tigation of Speller. 13 This author found that when 0.8 gram of iron in the form of ferric chloride was dissolved in 100 c.c. of hydrochloric acid, of the molarity given, shaken with twice its volume of ether, and allowed to stand 30 minutes at 17°-18°, the ether layer contained the percentage of iron given herewith: From the foregoing facts it results that two or three extractions with ether are sufficient to remove practically all the iron 14 from a 6 molar hydrochloric acid solution. The chlorides of thallium, 15 gold,16 tungsten and molybdenum,17 if present, are more or less completely removed with the ferric iron in the ether layer; the same thing is true of the chlorides of stannous tin and mercuric mercury.18 13 F. N. Speller, Chem. News, 83, 124 (1901). 14 The ether should first be saturated with hydrochloric acid by shaking it up with some 12 M HCl, otherwise if ordinary ether is used, the amount of hydrochloric acid in the aqueous layer will be decreased by each extraction. 15 A. A. Noyes, W. C. Bray, E. B. Spear, J. A. C. S. 30, 22 (1908). 16 R. Willstätter, Ber. 36, 1830 (1903), separates gold chloride from platinum chloride in aqueous solutions by extracting with ether. 17 Molybdenum appears to be but imperfectly separated in the absence of ferric chloride. W. Skey, Chem. News, 36, 48 (1880); A. A. Blair, J. A. C. S. 30, 1229 (1908); R. de Jong, Zeit. anal. Chem. 41, 596 (1902). 18 The chlorides of sodium, potassium, calcium, nickel, zinc and cadmium, and the thiocyanates of copper, nickel and zinc are soluble in anhydrous but not in aqueous ether: W. Skey, Chem. News, 36, 48 (1880). Stannous chloride is soluble in ether: M. de Jong, Zeit. anal. Chem. 41, 596 (1902). Phosphorus. If phosphorus is present as ortho-phosphate, a considerable portion of it, depending upon the amounts of iron and phosphorus present, goes along with the iron into the ether layer as shown by Wysor, 19 whose results are given in the following table: Rothe's Ether Method finds special application in the analysis of iron ores and iron and steel products when it is desired to determine the amounts of other elements that may be present with the iron, but present in small amounts only, in particular, copper, aluminum, chromium, titanium, vanadium, manganese, nickel, cobalt, calcium, magnesium and sulphur. The iron will go into the ether layer, the other elements into the aqueous layer as already mentioned, molybdenum and phosphorus (orthophosphate) will divide more or less between the two layers. 232. Procedure in the Case of an Iron Ore.20 Dissolve five or ten grams of the ore in hydrochloric acid. Evaporate the resulting solution to dryness on the water-bath and maintain at the temperature of the water-bath for twenty minutes or so to dehydrate silica. Add 50 c.c. 6 molar hydrochloric acid, digest for several minutes at 50°-60°, dilute with 50 c.c. water and filter off the residue, consisting of insoluble matter and dehydrated silica. Treat the residue in a platinum crucible with several c.c. of hydrofluoric acid and 2–3 drops sulphuric acid, evaporating 19 R. J. Wysor, J. Ind. & Eng. Ch. 2, 45 (1910). 20 In the case of a steel, dissolve two or three grams of the steel in nitric acid with the aid of hydrochloric acid if necessary. Evaporate the resulting solution to dryness on the waterbath and maintain at temperature of the water-bath for twenty minutes or so to dehydrate any silica. Add 30 c.c. 6 molar hydrochloric acid, digest for several minutes at 50°-60°, dilute with 30 c.c. water and filter off any silica. Evaporate filtrate on the water-bath until it reaches a syrupy consistency, add 10-15 c.c. 6 molar hydrochloric acid and transfer solution to a separatory funnel of about 150 c.c. capacity, using a little more 6 molar hydrochloric acid for rinsing purposes; the total volume of the ferric chloride solution in the separatory funnel should not exceed 50 c.c. From here on proceed as directed in main body of text. to dryness but not igniting. Dissolve the residue in hydrochloric acid, filter off any insoluble matter, and add the filtrate to main solution. The insoluble matter, which will be very small, is free of iron and therefore need not be included in the ether separation. It is fused with a little sodium carbonate or potassium pyrosulphate, the fused mass dissolved in hydrochloric acid, and the resulting solution subsequently added to the aqueous layers from which the iron has been extracted. The main solution, plus the filtrate from the hydrofluoric acid treatment, is evaporated to a syrupy consistency on the water-bath, 10-15 c.c. 6 molar hydrochloric acid are added, and the whole contents transferred to a short stem separatory funnel of about 150 c.c. capacity. If any of the ferric chloride solution remains behind, it is rinsed into the separatory funnel with a little 6 molar hydrochloric acid, but the amount of acid used should be kept as small as possible because the total volume of ferric chloride solution in the separatory funnel should not exceed 50 c.c. Cool the separatory funnel and its contents by holding under tap water, and add cautiously 50 c.c. ether previously saturated with hydrochloric acid. Mix the two layers by gentle shaking, meanwhile keeping the funnel under the tap water, as much heat is generated, and if the heat is not removed the consequent rise in temperature will cause the ether to reduce some of the ferric iron to ferrous, a result to be avoided since the ferrous chloride will go into the aqueous layer. Even with the most careful manipulation in shaking there will always be a considerable increase in the vapor pressure of the ether, and the caution must be carefully observed to open the stop-cock of the separatory funnel frequently during the shaking in order to relieve the pressure. After the contents of the funnel have been thoroughly shaken and mixed, the funnel is set aside for thirty minutes or so until the two layers have completely separated. The lower aqueous layer is then run into a second separatory funnel. The stopper and stem of the first funnel are carefully rinsed with 6 molar hydrochloric acid and the rinsings added to the second funnel. 50 c.c. of 6 molar hydrochloric acid are added to the first funnel, and the extraction repeated, after which the lower aqueous layer is joined with the one already in the second separatory funnel |