INDUSTRIAL A N D ENGINEERING CHEMISTRY
356
TABLEI. NEUTRAL EQUIVALENTS OF FATTY ACIDB Pdmitio acid
Calod. 256.3
Lauric acid
200.2
Myristic acid
228.2
Found 256.5 266.8 200.2 200.0 227.7 228.0
Semi-micromethod Found 256.3 255 256 200.2 200 201 199 228.2 229 227 227
VOL. 8, NO. 5
A few typical analyses, listed in Table I, indicate the real value of the method. Results which were carried out on a semi-microscale, using not more than 50 mg. of fatty acid and 0.017 N sodium ethylate, are also included. Aclrnowledgment The writers wish to thank the Carnegie Corporation Research Fund Committee for a grant which enabled the purchase of certain chemicals.
Literature Cited drops of methyl orange. Heat the tube in water at 65” C. t o ensure complete solution of the fatty acid, and titrate the acid with the standard ethylate solution. Use a ring stirrer and near the end point stir vigorously after each drop. Take the first appearance of green as the end point; it is quite distinct. Use a control tube containing 20 cc. of alcohol and 3 drops of methyl orange. Carry out a blank determination on 10 cc. of alcohol and subtract this value from the actual run. Standardize the sodium ethylate against pure stearic acid in a similar manner.
(1) Bishop, Kittredge, and Hildebrand, J . Am. Chem. Soc., 44, 135
(1922).
(2) Clark, IND.ENQ.CKEM.,20, 306 (1928). (3) Folin and Flanders, J . Am. Chem. Soc., 34, 774 (1912).
(4) Kolthoff and Furman, “Indicators,” pp, 92 and 183, New York, John W7iley & Sons, 1926. (6) Shriner, Fulton, and Burks, J . Am. Chem. Soc., 55, 1494 (1933). (6) Woolley and Sandin, Ibid., 57, 1078 (1935). RBCEIVED June 2, 1936.
Determination of Ferrocyanide Ion by Means of Luteocobaltarnrnine Chloride WALTER A. HYNES, MICHAEL G. MALKO, AND LEO K. YANOWSKI, Fordham University, New York, N . Y.
W
ILLIAMS (19) listed several procedures for the estimation of ferrocyanides. Of these, his own method ($0) seems to be the most accurate of the processes proposed up to that time. Hurter (IO),Knublauch ( I I ) , and Zalorecommending titration with zinc and copper salts, ziecki (U), were adversely criticized by several analysts, including Colman (8) and Lunge ( I S ) , the latter claiming that only 79 to 85 per cent of the ferrocyanide content determinable by precipitation as Prussian blue could be obtained by this process, while Leeds ( l a ) claimed that precipitated Prussian blue always gives results which are too low when ignited to the oxides. Skirrow (16) unfavorably criticized Feld (7) for his use of magnesium and mercury salts, but Colman (4) defended the use of Feld’s procedure and challenged Skirrow’s analytical results. The method proposed here is of approximately the same accuracy as that of Williams (ZO), which requires slightly less than 2 hours for completion, and which demands the attention of the operator continuously during the course of the analysis. In addition, the end point obtained on titrating the cyanide with silver nitrate (the first appearance of a permanent opalescence) is somewhat unsatisfactory and requires considerable practice on the part of the analyst until he becomes familiar with its appearance under varying conditions-viz., light, background, etc. A number of oxidimetric methods for the determination of the ferrocyanide present in both pure salts and gas-furnace residues have been proposed. These methods involve oxidation of the ferrocyanide by means of potassium permanganate ( I @ , potassium dichromate, ammonium persulfate, potassium bromate, and ceric sulfate. Some of these are strictly volumetric, while others are potentiometric in nature. The latest, involving potentiometric titration with ceric sulfate, was found accurate and ideal for routine analysis (8), but the other oxidimetric methods seem to have as many critics as they have proponents and defenders. Hence, they were not considered as controls in this work. Luteocobaltammine chloride, [Co(NH&,]CL, is prepared
according to Biltz, Hall, and Blanchard ( I ) , recrystallized, and dried to constant weight, the purity of the compound being then established by gravimetric determination of the chloride ion. The luteo salt reacts with ferrocyanide ion in neutral aqueous solutions to form luteocobaltammine ferrocyanide, [ C O ( N H ~ ) ~ ] ~ [ F ~ ( first C N ) reported ~]~, by Gibbs and Genth (9), and later by Braun (2). Ephraim and Mosimann (5) also prepared this compound, and Steinmetz (17) studied its crystallographic properties. These authors state that the compound is difficult to analyze because of the presence of adherent moisture, and for this reason recommend either ignition to oxides of the metals present followed by reduction to the free metals, or decomposition of the compound with concentrated sulfuric acid followed by gravimetric determination of the sulfates. All agree that the substance is almost insoluble in water. Steinmetz specifically states that it is markedly more soluble in hot water, from which i t does not separate unchanged, and that i t is rather easily soluble in warm 20 per cent ammonium chloride solution, from which crystals of measurable size separate. Measurable crystals also form from solutions in dilute hydrochloric acid, provided the concentration of the acid is not increased by evaporation. The authors have found, as was to be expected, that the compound is also insoluble in organic solvents. KOdata can be found in the literature as regards the actual solubility of the luteocobaltammine ferrocyanide, and the authors’ attempts to determine the solubility of this salt have not been successful, probably because of decomposition of the suspended salt in pure water at 20” C. The results obtained varied between 52 and 66 mg. per liter. The suspension tends to become olive-green after agitation with water for 2 hours, the color deepening as time goes on, until a t the end of a week a greenish sediment appears mixed with some of the original material. This was not analyzed because of difficulty of separating the two substances. It was found impossible t o use the hexamminocobaltic
SEPTEMBER 15, 1936
ANALYTICAL EDITION
ferrocyanide as a gravimetric determinant for ferrocyanide ion, because of its instability as shown by the following experiments: On exposure to acidic drying agents-e. g., phosphorus pentoxide or concentrated sulfuric acid-decomposition occurred. At the temperature of boiling ether in an Abderhalden drier, approximately 72 hours were required for this decomposition. The result was a tan-colored product from which the original compound could be regenerated by exposure to ammonia vapors. At the temperature of boiling water, a dark-brown, almost black, substance was obtained in 48 hours, from which the original salt could not be regenerated on exposure to ammonia fumes. Further work is in progress on these decomposition products. E i d e r the conditions prevailing during the determination of ferrocyanide ion by this procedure, of the commoner anions only chromate, dichromate, and metavanadate ions interfere. Parks (14) and Parks and Prebluda (15),in fact, suggest the use of this reagent for gravimetric quantitative determination of vanadium. Ferricyanide ion, contrary to the statements found in the literature, did not precipitate under these conditions, and, as was pointed out to the authors (in a private communication from V. K. LaMer, who stated that he had suggested use of such complex salts as qualitative and quantitative reagents some years ago), this may have been due t o relatively high concentrations of the anions or t o the order of addition of the reagent and test solutions, although this latter consideration seemed of no influence in the case of the ferrocyanide.
Quantitative Procedure Salt used: crystalline potassium ferrocyanide. Reagent: 0.15 M aqueous solution of hexamminocobaltic chloride. METHOD.Weigh out 0.1 to 0.2 gram of the ferrocyanide in a 125-ml. beaker, and dissolve the sample in 15 to 20 ml. of water. To this solution add sufficient reagent to assure complete precipitation. Allow the precipitate to settle and filter through a Gooch crucible which has been ignited to constant weight. Wash thoroughly with ice water (distilled water kept in the refrigerator will suffice for this purpose) to remove excess reagent. The washing may be considered complete when the filtrate is no longer colored. Care must be taken to use the minimum amount of wash water, as an excess tends to lower the results. Dry the crucible in an oven at 100” to 110” C. for 0.5 hour. Ignite slowly over a Bunsen burner until the entire mass in the crucible has ceased to glow. Then ignite strongly for about 30 minutes over a Meker-type burner. On ignition over the Bunsen burner, ammonia and hydrocyanic acid gases can be readily detected. Cool and weigh. The computations in Table I are based on the assumption that the precipitate is [Co(NH3)6]1[Fe(CN)e]3. Thus, from 18 K4Fe(CN)~.3H20the ignited precipitate contains 8 c0304 9 Fe2O3. In this determination, the amount of ferrocyanide ion remaining in the filtrate and appearing in wash water has been found insufficient to react directly with ferric chloride and hydrochloric acid to give Prussian blue. On prolonged boiling with concentrated sulfuric acid, ferric hydroxide could not be precipitated in the acid liquid on treating with excess ammonium hydroxide. From the mixed ignited oxides i t was calculated that
+
357
Co:Fe = 1:0.7028. On determining the iron by Rothe’s ether method followed by Zimmermann-Reinhardt determination, it was found that Co:Fe = 1:0.6838. Fales ($) states that this method is slightly low for iron. From Co24Fe18069, iron should be theoretically 41.12 per cent and on reducing the ignited metals with hydrogen an average of 40.61 per cent of iron was found. TABLEI. DETERMINATION OF FERROCYANIDE ION NO.
Sample Gram
Oxides Gram
Fe(C!N)e Calcd. Found Gram Gram
1 2 3 4 5 0 7 8 9 10
0.1043 0.1007 0.1180 0.1222 0.1097 0 . 1783 0.1547 0.1133 0.1565 0.1846
0.0461 0,0442 0.0520 0.0539 0.0485 0.0783 0.0681 0.0500 0.0692 0,0814
0.05052 0.05227 0.05232 0.05012 0,05920 0.05896 0.06130 0.06112 0.05500 0.05500 0.08945 0.08878 0.07760 0.07722 0.05680 0.07850 0.05670 0.07847 0.09261 0.09230
Recovery Difference % % 99.90 99.21 99.60 99.70 100.00 99.25 99.51 99.82 99.96 99.66 Av. 99.66
-0.10 -0.79 -0,40 -0.30 0.00 -0.75 -0.49 -0.18 -0.04 -0.34
Conclusions Luteocobaltammine chloride may be used as a quantitative precipitant for the ferrocyanide ion, in the absence of chromate, dichromate, and metavanadate ions. Results compare favorably with standard methods. This method does not require much skill on the part of the operator, nor is his attention required except during the actual precipitation, filtration, and f i s t stage of the ignition, a total of approximately 25 minutes. Literature Cited Bilts, Hall, and Blanchard, “Laboratory Methods of Inorganic Chemistry,” 2nd ed., p. 175, New York, John Wiley & Sons, 1928. Braun, Ann., 125,182 (1863). Colman, Analyst, 33, 261 (1908); J . SOC. Chem. Ind., 27, 806 (1908). Colman, Analyst, 35, 295-301 (1910). Ephraim and Mosimann, Ber., 54,396-401 (1921). Fales, “Inorganic Quantitative Analysis,” p. 277, New York, Century Co., 1925. Feld, J . Gasbeleucht., 46, 561, 603, 629, 642,660 (1903). Furman and Evans, J. Am. Chem. Soc., 51,1128-33 (1929). Gibbs and Genth, J. prakt. Chem., 72,161 (1857). Hurter, Chem. News, 39,25 (1879). Knublauch, J.Gasbeleucht., 33,450 (1891) ; 55, 713-18 (1912). Leeds, Analyst, 22,9 11897). Lunge, Diwlers polytech. J., 246, 282 (1882). Parks, M., Dissertation, Columbia University, New York, 1930. Parks, W., and Prebluda, J . Ana. Chem. SOC., 57, 1676-8 (1935). Skirrow, J . SOC.Chem. Ind., 29,313 (1910). Steinmets, 2. Kryst., 57,233-52 (1922). Tcherniac, Dinglers polytech. J., 245, 171 (1882). Williams, “Chemistry, Manufacture, and Estimation of Cyanogen Compounds,” 1st ed., p. 343, London, J. & A. Churchill, 1915. Williams, J . SOC.Chem. Ind., 31,468-71 (1912). Zaloziecki, 2. angew. Chem., 3, 210, 301 (1890). RECEIVED September 10, 1935. Presented before the Division of Physical and Inorganic Chemistry at the 89th Meeting of the American Chemioal Society, New York, N. Y., April 22 to 26,1935.
