The Precipitation of Iron as a Basic Acetate Citation Baxter, Warren Phelps (1924) The Precipitation of Iron as a Basic Acetate. Bachelor's thesis, California Institute of Technology. doi:10.7907/X6WW-PV88. https://resolver.caltech.edu/CaltechETD:etd-04192004-142344 Abstract No Abstract. Item Type: Thesis (Bachelor's thesis) Subject Keywords: Chemistry Degree Grantor: California Institute of Technology Division: Chemistry and Chemical Engineering Major Option: Chemistry Thesis Availability: Public (worldwide access) Research Advisor(s): Unknown, Unknown Thesis Committee: None, None Defense Date: 1 January 1924 Record Number: CaltechETD:etd-04192004-142344 Persistent URL: https://resolver.caltech.edu/CaltechETD:etd-04192004-142344 DOI: 10.7907/X6WW-PV88 Default Usage Policy: No commercial reproduction, distribution, display or performance rights in this work are provided. ID Code: 1413 Collection: CaltechTHESIS Deposited By: Imported from ETD-db Deposited On: 22 Apr 2004 Last Modified: 03 Oct 2019 23:08 Thesis Files Preview PDF (Baxter_wp_1924.pdf) - Final Version See Usage Policy. 986kB Repository Staff Only: item control page

THE PRECIPITATION OF IRON AS A BASIC ACETATE Warren P. Baxter In partial fulfillment of the requirements for the degree of Bachelor of Science in Chemistry California Institute of Technology Pasadena, California 1924 THE PRECIPITATION OF TRON AS A BASIC ACETATE. By Warren P. Baxter. INTRODUCTION. The object of this investigation was to determine the aeture of the factors which influence the precipitation of iron as a basic “acetate and the extent to which these could be varied with the view that such knowledge would help in nerfesting the present basic acetate separations and in working out new ones. Some of these factors are the volume of the solution,end the amount of iron, the coneentra- tions of acetic acid and acetate ion, and the presence of other substances. As an example of the latter, the effect of cerium in hindering the precipitation of iron invites question as to whethor this effect is colloidal in nature or is due to mass-action changes and complex-ion formation. A review of the literature shows that most of the work done on the precipitatioa of iron by this method is largely empirical in question, and gives descriptions of analytical procedures without extended study of the underlying principles. A list of the more importent works consulted is given below. EXPERIMENTAL PART. The first chese of this question investigated was the determin- ation of the maximum concentration of hydrogen ion at which it was possible to secure comblete precipitation of the iron. From the results of Mittasch ‘ who took 300 mg. of iron in a volume of about hac ec. with varying amounts of ammonium acetate and acetic acid and determined the weight of the precipitate, the greatest hydrogen ion concentration which gave complete precipitation was calculated to be 2 > from 4 to .7 x 197? molal. From the results of Funk who made a similar series, the value 5 to 9 x 107 Was calculated. These ‘results are rather doubtful because of the uncertainty of the initial hydrogen ion concentration and the composition of the precipitate. Accordingly, in order to more accurately determine thie value, 2 series of. experiments was made in which only a small amount of iron was taken and the initial concentrations of acetic acid and acetate were known. For the purposes of these and other experiments the following solutions were used. | | Stock solution of ferric nitrate 645k mg. / cc. tt Test solution of Fe 19.0 mg. / cc. Acetic acid solution 6.90 Normal Sodium hydroxide 6.80 " Sodium acetate solution ~ 3,00 " Standard HCL solution 9.6916 * Stendard base 0.4507 " The Be(H0z)- stock solution was vrepared from Baker's ¢.P. Ferric Nitrate. It wes stendardized by precipitating the iron with ammonium hydroxide, igniting, and weighing. The solution containing ma ttt he 33 ‘ 10 mg. Fe per ce. was prepared from this by diluting to the % calculated volume. The sodium acetate solution was prepared from the 6.00 N HAc and NaOH by mixing equal volumes of the two solutions. The method of making the exseriment was to take 10 mg. of iron, add measured quantities of acetic acid end sodium acetate, make up to 100 cc., heat to boiling and continue gentle boiling for a definite length of time. . The orecipitetions were made in 390 ec. Erlenmeyer flasks in the opening of which was placed a flanged test-tube contein- ing cold water which prevented undue evaporation during the boiling. ‘The solution was then filtered while still hot and the amount of precipitate estimated. When precipitation was nearly connlete the iron in the filtrate was estimated colorimetrically with KSON. The results of these experiments are given in Table 1, The concentrations of the acetic acid and acetate are corrected for the amount of iron precinitated. The composition of the precipitate is unknown but statements in the literature end experiments will leter indicate that it is approximately one mole of acetate to two mols of iron (see Comvosition of Precipitate below). Therefore when io mg. of iron was precivitated it was assumed that 0.0005 equivalents of acetic acid were set free and the same amount of sodiun acetate used up. The ratio HAc / Nase wes based on these corrected concentrations. TABLE OF EXPERIMENTS. Normalities and ratio HAC / NeAc calculated Volume of sclutien 100 cc. Iron taken 10 mE « after precipitation hes taken place. No. | 6N HAc | 3N NeAc | Time of Normality ‘Normality Ratio Precipi tate Filtrete Remarks poiling , Bxp- CCe CCe minutes HAc NaAc Hac / NaAc | mg. Fe 1 5.0 1.0 1.2 0.300 ‘0.030 10.0 trace colored 2 5.0 2.0 1.2 -300 2060 5.0 eme 11 colored 3 50 5.0 1-2 2305 2145 2.1 19 no color 4 5.0 3.0 1-2 305 085 3.6 to no color 3 50 2.5 4 1+2 302 073 44 3 colored 6 5.0 2.5 1 = 2 -302 .073 44 4 colored 7 5.0 2.7 1-2, 305 2076 ho . 10 no color 8 5.0 2.6 “4 .301 O77 | 53.9 4 colored 9 5.0 2.7 1 301 .080 348 2 colored Ts) 5.0 3.0 fe) 6301 2089 3.4 1 colored | Ho. | 6H Hie | 38 NatAo fine Tad Hormality | Normality | Retie _ | Presipitate \ Piltrate. | Remit ‘Exp. Be: GCe minutes - Hac NeAdc Hac / Nedc \_ mg. Fe. iF 5.0 3.0 ' 0.305 0.085 3.6 | 10 | light color 0.5 mg. Fe in fil 12 5.0 3.0 2 0.305 2085 3.6 10 no col. 0.04 13 5.0 5.0 5 1305 085 3.6 10 no col. .08 14 5.0 2.5 2 2303 072 4.2 5 1. col. 0.5 15 5.0 2.5 5 bd 070 ALA 10 no col. .02 16 5.0 2.0 5 304 0056 | 5.4 5-8 1. col. 0.6 17 5.0 2.7 3 -305 076 4eo 10 no col. .03 18 3.0 2.5 3 2305 “070 444 10 no col. ,1 19 10.0 4.8 3 602 142 4.2 4 colored 20 15.0 7.5 3 900 £225 hoo 0 af 25 [41 5 2155 050 5.1 colored 22 2.5 1.5 5 6155 L040 3.9 10 no col. .04 23 2.5 1.3 3 2154 +035 4.4 colored a4 10.0 7-0 y £03 207 a9 5.8 colored He. | GN Has | 3H Wake wane ot Yomormali ty - Normelity - Retio [. precipitate | Filtrate | = Remarke Exp. ec. ec. minutes HAc NeAc Hac / Neds mg. Fe 25 10.0 10.0 5 0.604 0.296 2.0 9 le col. 1 mg. 26 | 12.5 | 12.5, 5 3 0 4, 200 mg. Fe ? 300 ne col. «3 Volume 500 ¢c. 27 5.0 2.5 3 305 +070 4,4 10 ist. part 1. 5 g. NaCl last no col. added 28 5.0 2.6 3 305 .073 4.2 5 g- NaCl 10 no col. .03 added 29 7.5 3.7 3 455 .106 4.30 10 jet. part la last part of col. filtrate no col. 30 8.5 4.2 3 2515 121 4,25 9-10 1. col. .5 31 9.0 454 5 545 1125 435 10 1st vart 1. last part a. . gol. colorless 32 9.5 4.60 3 571 137 4,16 2 colored 3% 11.0 5.26 3 -660 0158 4.18 0.5 colored 34 12.0 prey, b) 0720 166 4433. 0.1 colored 39 10.0 4.80 5 £02 42 4.25 | 5 colored 36 10.5 4 86 3 630 » 146 4.51 1 colored 37 9.5 4.50 3 572 . 133 4.36 5 colored 38 | 9.0 | 4.34 3 545 1125 436 to no col. .3 a:| ON tee: [oN meas | Tine of bclermelity | Normiity | Ratio” | preectpitate | Bp. | eo. | cee veaatoe | _ Hhe "Nake tthe /Nete | mg. Fe | RAtrate: Remarks 39 | 5.9: 2.20 5 0.305 0.061 5.00. 10 no col. .2 ko 75 3.20 3 454 002 4.94 8 colored AY 8.5 3.60 % 512 «106 4,84 5 n 4a 10.0 4.00 5) 602 2118 5.10 54 n Ag 12.0 484 3 .720 145 4.07 51 " Ab 15.0 6.00 ; -900 » 180 5.00 4, " ? As 15.0 6.00 3 2900 180 5-00 0.1 " 46 10.0. 5.04 3 605 N73 5.50 lo l. col. 15 4 15.0 8.67 5 900 266 5.46 0 colored Ag 12.0 6.99 5 720 . .207 3.48 | 1 r 4a 5.0 2.00 9) 301 4059 51 1-2 n ) 50 5.0 2.00 5 305 1055 D6D 10 l. col. herd to filter 51 5.0 2.90, To -305 O55 DD 10 no c@l. .o4 ppt. coaguleted 52 5.0 2.00 3 2303 2057 5.3 5-7 colored Mo. | 6M Hic | 5N Nadc | Time of | Normality | Normality} Retio | Precipitate | CS . boiling ‘Filtrate Remarks | Exp. aCe GCe minutes | Hie NadAe Hae / NaAc mgs Fe 53 3-3 oye) °) | 200 1. color 200 mg. taken 54 3.3 559 3 200 no color a R 35 53 5.39 lo 200 -no color "oof a 56 fo) 5.0 1 200. no color oA " 57 15.0 15.0 3 2901 4D 2,00 1.5 -2 colored 58 12.0 12.0 5 .721 1350 2.01 3 " 50 20.0 | 20.0 y 1.200 «600 2.00 0 " ‘ : 60 1. 6.0 1 200 no color 200 mg. taken to DISCUSSION OF RESULTS. In Curve 1 are show disgramatically the results of Exp. 1 - 7, and 12, 14, for which the time of boiling is one to two minutes and the - amount of 6N HAc taken is 5.0 cc. The ratio HAc / NaAc is plotted against the mg. of iron precipitated. It is seen from the curve _. that precioitation is complete with a ratio of 4 or less. The '. sharmmess of the break seens rather remarkable in view of the influence of the time of boiling on the completeness of the precipitation. Thus in Exp. 15 and 18 with three and five minutes heating the precipitation is complete even with a ratio of 4A, The results discussed below _ also make this curve less significant from mass-action effects. _ However, such a break would be sharp if these effects were the deciding factor since the amount of iron is small. LENGTH OF BOILING. The length of boiling is an importent factor in the precipitation of the iron. . In the literature emphesis is placed on the necessity of only a short period of boiling in order to avoid slimy precipitates that are difficult to filter. Most directions call for a period of heating of from one to two minutes. In the experiments with only & small amount of iron present the length of boiling was found to have practically no effect on the character of the precipitate. Most of the precipitates obtained were somewhat difficult to filter. but no better results were obtained even with very short boiling. In the first eighteen experiments 5 cc. 6N HAc were used, the NaAc ( 3.N ) varied from 2.5 to 3.0 ce, and the time of boiling from one to five minutes. Curve Ff, (Exp. (-7,/2,/4) ” Ra t/0 HAC Wig Ac plotted against i “completeness of precipitation. Time of boiling HAC /-2 Min. Fee } 7. 2 . #, Lng Fe pata. Curve ® 2 | Effect of length of F/imé of boiling @ Exo 49-52 S3B-5F (5: Oce. HAc , 2-00cc Naie) | 3 mg. Fe in filtrate 11 ‘ghe.resulte indiceted that a time of three minutes was preferable for complete precipitation but that longer hee eting was unnecessary. Accordingly, boiling for three minutes was adopted for most of the subsequent work. | The effect of boiling on the completeness of precipitationis | shown in Curve 2 ( Exp, 40 ~ 55 ). Solutions containing 10 mg. of tron, 5.0 cc. HAc and 2.0 ec. Nadc were boiled for various times. ‘There is almost no precipitation on heating just to boiling, but five minutes gives very fair orecipitation, while ten minutes gives complete reaction. A similar tendency is shown with larger amounts of iron. Exp. 53, $4, and 55 with 200 mg. iron gave very sliny precipitetes, ut the longer boiling gave slightly more easily filtered solutions. In “these experiments, the effects just mentioned are not due to "boiling ‘out the acetic acid from the solution, since in every case a test-tube filled with cold water was placed in the mouth of the flask and acted efficiently as 2 reflux condensér. . The results of Exp. 27 and 28 indicate that the addition of five . of precipitation grems of Natl has no noticeable effect cither on the completeness,aor on the character of the precipitate. The effect of the presence cf wee—prenence—oF other substances was not determined. It is stated that the initial concentration of acid mst be small in order to give & precipitate that is easily filtered and washed. This is borne out by Exp. 56 and 60 in which 200 mg. of iron were taken. in one experiment 5 cc. NeAc but no HAc was added, in the other i cc. HAc and 6.00 ce. NaAc were used. In the first ease the precipitate obtained was very similar te thet obteined with the use of emmonia and 12 wee easy to filter. The other, however, was somewhat more slimy and more difficult to handle. EFFECT OF CONCENTRATION OF ACETIC ACID. The experiments to determine the effect of the total acetic acid present yielded resulte that appear rather surprising. The nature of the phenomena is illustrated in Curves 3 and 4, The ‘manner of carrying out the experiments was the same as before except ‘thet in each series the ratio HAC / NeAc was kept constant, only the total concentrations of these reagents being varied. Thus for Exp. 18, 19, 20 ~ 38 the ratio HAc / NeAc was meinteined et 4.35 but the HAc was varied from 5 to 12 cc. added initially. The amounts of acid end acetate used were calculeted for a given ratio on the assumption that the precipitation would be complete. If the precipitation wes not complete, the ratio would be less than calculated, but this-.only makes the results more certain. It is seen in Curve 3 that precipitetion is complete when 7.5 ce. of ecid are taken but with 11 ec. there is almost no precipitation. In Curve 4 are illustrated the seme Phenomene for ratios of 5.00, 3.50, and 2.00. _ The nature of the results is, however, best seen in Curve 3, in which the number of experiments is greater. Presumably, with the same ratio of acid to acetate, the hydrogen ion concentration is constant unless the activities of these two substances vary differently with concentration. Por any usual mass-action expression for the formation ef basic ferric acetate the concentration of the acetate ion is raised to a higher power than the acid. Accordingly, it would be expected that incressing Curve #3 (Exp 18,19, 29-58 } Ratio HAC/NaAc = 4:55 re . | ng te nod precitared bia /0 Curve #4 QO MAC/MAc x _ “ ? (Exp. 39-46) nod NWO Sas i 4 2 mg Fe potd 13 the concentration ef both the HAc and NaAc would give more certain precipitation, thet is, the lines would slope in the opposite direction from the observed. The crossing of the lines in Gurves 3 and 4 ie probebly cue to the inexact qualitative nature of the experinents. In general, however, the curves show that for any particular concen- tration of acid the precipitation is more complete for greater amounts of Nadc. In experiments with large quentities of acid it was ; noticed that the deep red color characteristis of the solution juat before precipitation took place was absent. J. Jewett hes revorted this effect of large quentities of acetic acid. "He further ascertained thet iron could not be precipitated in presence of a large amount of acetic acid by increasing the amount of sodium acetate." | Possibly the explanation of the effect is to be found in the chemistry of colloidal iron produced from acetate solutions. COMPOSITION OF THE PRECIPITATE. | Textbooks of quantitative analysis * give the composition of basic ferris acetate as Fe(OH) Ac. It is unlikely that the precipitate is as simple as this and possibly varies through rather wide limits under different conditions. Weinland ? hes studied the salts of ferric acetate complexes and has show that solutions of Fe(OH), in acetic acid contains the acetate of a hexa-~acetatetriferric y a) Treadwell and Hall, Quentitetive inalysis, Sth. ed., p. 152. A. A. Noyes, Qualitative Analysis, 8th. ed., p. 105. 14 | getd~conteinthe-neeterte-of~e--hexeuscetetetriferrte base. The cation ve +t os Le acid Fez( C2109 )¢ is the basis of the FeCl, reaction for acetic acid. 3 FeCl, + 9 Nake + 2 Hg0—> 9 NaCl + Fez(GpH,09)g(CgHs0g)(OH)g + 2 Hac Wienland made two series of experiments on the composition of the ordinary basic acetate precipitate; (1) varying the volume of the solution, (2) varying the amount of sodium acetete. The results obtained lie - glose to the value of one mol of acetate to three mols of iron. “With 390 - 1500 cc. volume he found Fe / Ac as 3 / 0.88, while with 190 cc, the proportion was 3 / 1.04. .With 2 g. NaAce the proportion was 3/ 0.88, with 3g. 3 / 1.14, ando a 3 / 1.17. He assigns the composition of the dried precipitate as Fes( C2H302)( OH) 203. 0.F. Tower ? determined the composition of basic ferrie formate and obtained also this forma. It was desired to determine the composition of the precipitate under somewhat more varying conditions. | By taking definite volumes of the standard iron solution it would only remain to determine the acetate in the precipitate. It was thought that distillation with “phosphoric acid and titration of the distillate would accomplish this easily and accurately but it wes found that the pronounced tendency of the mixture to bump made the method impractical. _A combination of straight and steam distillation from a sulphuric acid solution was next tried and blank experiments showed that the method would be satisfactory. However, only two preliminary determinations were made. Five cc. of Fe solution and 8 cc. Nadc were made up to 200 cc., heated 15 - to boiling, end boiled for three minutes. The precipitate was piitered. with the aid of suction and washed with hot water until the washings no longer discolored 2 drop of NaOH in phenolohthealein solution. The filter and precipitate were transfered to a beaker and 5o cc. of ‘standard KOH added, together with 100 ec. of water. This mixture was boiled for ten minutes, allowed to cool, and then titrated with HCl. After 20 cc. of acid had been added to the mixture, it was - Piltered and washed, and the titration completed. Volume acid, 32.30 Cl. This gives Fe / Ac as 3 / 1.61. In the second determination the amounts of material taken and the procedure were the same excep thet it was also attempted to determine the acid in the filtrate. The first 100 ce. of filtrate was titrated with standard. base ;( 17.77 ec. base, 9.04 ce. acid }. This gives ratio of 3 / 1.00. _ However, the loss of solution by evaporation during the filtration renders this result worthless. The precipitate was washed, boiled for a half hour with 25.00 ce KOH, diluted to 100 ce., filtered through a dry Pilter, and 50 cc. of the filtrate titrated with HCl solution. Stendard heid, 6.83 ce. Fe / Ac = 3 / 1.59. The investigation was discontinued at this point. ont CN SUMMARY AND CONCLUSIONS. A number of basic acetate precipvitations have been made taling 10.mg- of iron and determining the effect of varying the amounts of sodium ecetate and acetic acid and the length of boiling on the character of the precipitate and the completeness of precipitation. The results have been illustrated by several diagrams. These experiments indicate thats 1, The length of boiling has only a slight effect on the character of the precipitate. | 2. . Inereasing the length of boiling increases the completeness of the precipitation. _ 3. Increasing the amount of sodium acetate increases the completeness of precipitation. 4. The reaction cannot follow any simple mass-action expression. Curves 3 and 4 illustrate 2 phenomena which has not yet. been explained. Two determinetions give the composition of the precipitate as Fe / Ac = 3 / 1.60. The precipitate may therefore consist of approximately equal amounts of Fe(OH), end Fe(OH) sAc. 1. Se 17 BIBLIOGRAPHY. A list of only the most useful articles is given here. A. Mittesch. The Accuracy of the Acetate Method for the Separation of Iron and Manganese. Zeit. anal. Chem. 42, 402 - 500, (1003). W. Funk. Separation of Iron from Menganese, Nickel, Colbalt, and Zine by the Acetate Process. - Zeit. anal. Chem. 45, 181 ~ 105, (1006), W. Funk. | Separation Of Iron from Manganese, Nickel, Colbalt, and Zinc by the Formate Process. | | Zeit. anal. Chen. 45, 480 .~ 504, (1906). Jom Jewett. - Influence of Acetic Acid on the Separation or Iron as a Basic Acetate. | Am. Chem. J. 1, 251 ~.255, 1879. ‘Weinland and Guasmann. On Ferric Acetate and the Acetic Acid Reaction with Ferric Chloride, also the " Basic Precipitate"; Zeit. f. anorg. Chem. 65, 157 - 168. R. F. Weinland. Chromi and Ferri Acetates. Chem. Zeitung. 35, 1096 ~ 7, (1012). 0. F. Tower. Precipitation of the Iron Group and the Composition of certain Ferri Formates. J. Am. Chen. Soc. 32, 953 - 7, (1910). “10. 1@ We Hera. Decomposition of Ferric Acetate. Zeit. enorg. Chem. 20, 16 - 20, (1800). B. Reinitzer. Reactions of the Acetates of Chromium, Iron, and Aluminun. Monatsh. Chem. 3, 249 ~ 265, (1882). ‘Lundell and Knowles. The Separation of Iron and Aluminun from Manganese and Gertain Other Elements. J. Am. Chen. Soc. 45, 676, (1925). PART B. ANALYSIS SG OF THE IRON GROUP. ‘In connection with the work on the precipitation of iron as a pagie acetate some experiments were made on a proposed modification of the analysis of the iron group. In the present method for the detection of manganese ‘by potassium chlorate in concentrated nitric acid solution (procedure 61. A. A. Noyes, Qualitative Analysis) small quantities of manganese are sometimes missed; by the filter paper pulp present in the solution. Possibly due to the reduction of the KC10, of nickel and cobalt from iron with ammonia is unsatisfactory because of the large fractions:carried down by much ferric hydroxide. It was ‘thought that the following scheme would offset these difficulties to some extent,and in general be more simple. ANALYSIS OF THE IRON GROUP. Precipitate: Fe(OH)» MnO » Ni(OH)o, Gol OH)s, (Zn, alkaline-carths). Treat with HCL, add NaAc anc heat. Wmnt*, Nit’, Cot?, (2n, alkalinesearths). Precipitate Solution: Fe(OH) jAc. _ Add Bry and heat. Precipitate Solution: Mit*, Cot, (2n*t, Minds ‘alk, -cearths ). Follow usual procedure. If vchosvhate was present the srecedure would be the same except that a separate small portion would be tested for’ iron anc also iron added to the main portion with the sodium acetate unless a red precipitate had already formed. Also, the seperation 20 The first point investigated was the conditions under which | * nanganese would be precipiteted by bromine in acetic acid, sodium acetate solutions. Caloulation showed that with about 500 mg. Fe and using 15 co. 3N NaAc, with volume 100 - 150 ¢c., the concentrations of Hic and NeAc after preci olitetion of the iron would correspond to 5 cc. 6N HAc and 7 cc. 3N Nac in 100 cc. Experiments were made using these and _other concentrations with various amounts of manganese and bromine and ' determining the effect of heating. The following procedure was found to give complete precipitation of the manganese. Add tec. & on £ & (om) liquid bromine to the solution, shake for about 2 minute, heat on the water bath for 5 minutes, boil until bromine fumes are no longer noticeable, and then boil five minutes longer. (Derk brown or black precipitate; presence of manganese.) Filter. If the precipitate is more than 100 mg. add 1.3 cc. 6N NaOH to the filtrate and 0.2 ce. bromine and boil for five minutes. This is a very sensitive test for manganese and 0.1 mg. can be detected because of the dari color of the precipitate. Although ‘most of the manganese is easily precipitated, the last few traces are difficult to get dom, but the above procedure gives satisfactory results. The brecivitate is quite compact and the hot solution is easy to filter. A couple of trial anelyses were made with 500 mg. Fe and 1 mg. Mn and both gave a very distinet test for manganese by this method. So far this method would seem to be very satisfactory, but the “behaviour of cobalt end nickel with biouine renders the method worthless. Five hundred milligrans of cobalt was taken with 15 ee. NaAe and 1 ce. HAc and treated with bromine according te the above procedure. — During } ct ~~ ss = 2 ° , the heating a black slimy precipitate forued,(about 40 mg.). 21 | The filtrete wes vink colored. it was neutralized with sodium hydroxide, “4 ec. HAc added end then 1 cc. bromine, and the mixture heated. A black precipitate forned, (150. mg.). The filtrate was colorless. . Five bundred mili grans of nickel with 15 ec. NaAc, 1 cs. HAc, and 1 cc. bromine in 100°ce¢. solution was heated for five minutes and then boiled to exvel the bromine. About fifty milligrams of a dark colored preeipitete formed. . The filtrate was green. “While these results render this proposed method for the iron group useless, possibly conditions could be worked out for the separation of cobalt from nickel by means of bromine in acetate solutions which would serve better than the present tests with dimethylgloxime and notassium nitrite. With respect to the oxidation of cobalt Lundell ( J. Am. ? Shem. Soc. 45, 2600,(1923) shows that cobelt interferes with the bismuthate method for manganese because it is oxidized.