INDUSTRIAL AND ENGINEERING CHEMISTRY
October 15, 1931
Experiments of this sort gave rise to the hope that this was a method of separating calcium and strontium quantitatively.
Unfortunately, however, the solubility of strontium p-bromobemoate is remarkably increased by the presence of other metallic ions, including the calcium ion. A solution containing equal amounts of calcium and strontium nitrates gives a very slight precipitate, even when the concentration of the strontium salt is 10 or 15 mg. per cubic centimeter. If the concentration of calcium nitrate is increased to three or four times that of the strontium nitrate, precipitation is entirely prevented. All efforts to avoid this difficulty have been unsuccessful. In the hope of effecting a separation of calcium and strontium, comparisons have been made of the solubilities of several other halo-benzoates of these two metals. I n no other case, however, was there any great difference in solubility, either in water or in water-acetone mixtures. Qualitative tests have shown that if a chlorine, bromine, or iodine atom is in the ortho position to the carbonyl group, the salts are many times more soluble in 94 per cent acetone than if the halogen atom is in the para position; the few meta-substituted salts studied show an intermediate solubility. In any case, the solubility
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decreases markedly with increasing atomic weight of the halogen. Table I gives the solubilities of the para-substituted salts in 94 per cent acetone a t room temperature. (The ortho- and meta-salts were not studied quantitatively.) It will be seen that all of the p-iodobenzoates are quite insoluble in 94 per cent acetone. The large equivalent weight of iodobenzoic acid should make it an excellent precipitant for the quantitative determination of the alkaline earth metals. A study of this may be made a t a later date. of Alkaline Earth Halo-Benzoates i n 94 Per Cent Acetone (Expressed in millimoles per 100 cc ) HAI.O-BEN70ATE CALCIUM STRONTIUX BARIUM p-c1 2.9 0.1 0 007 p-Br 1.79 0.028 less than 0.003 P-1 0.16 0.026 less than 0.003
Table I-Solubility
Literature Cited (1) Fresenius, Z . anal. Chem., 89, 189 (1893). (2) Hillebrand and Lundell, “Applied Inorganic Analysis,” p 490, Wiieq., 1929. (3) R a w o n , J . SOC.Chem. Ind.. 16, 113 (1897).
Electrolytic Determination of Cobalt‘ Dorothy H. Brophy RESEARCH LABORATORY, GENERAL ELECTRIC CO., SCIIBNECTADY, N. Y.
HE use of c o b a l t in
A rapid electrolytic method for the determination This electrolytic s o l u t i o n of cobalt has been described. This method makes use served as a basis for the expermanent m a g n e t s and cemented t u n g of a rapidly rotating anode (800 to 1000 r. P. me), a gauze periments. If the solutions sten carbide brought about cathode, and an electrolytic SolUtion consisting of were stirred, the electrolysis the necessity of a more rapid ammonium chloride, ammonium hydroxide, and required from 6 to 7 hours. sodium bisulfite in amounts adjusted as described A current density of 3 amp. method for its determination. Electrolytic separations are in the d k i c ~ ~ i o n . per sq. dm. was maintained and the electrodes were kept a l w a y s very attractive for BY observing the m ~ m m e n d e dprecautions, it is rapid a n a l y s e s , b u t h a v e possible to remove from 15 to 160 mg. of cobalt in a 4cm.apart. Ahemicylindrinever been h i g h l y recomhalf hour and obtain bright, adherent deposits in cal cathode, 9 x 5 cm., with mended for cobalt, possibly which the amount of sulfide has been s w h ~ ~tod 8 a wire a n o d e was used for owing t o t h e i n a b i l i t y to negligible quantity. these experiments. reproduce r e s u l t s following Organic acids, hydrazine sulfate or hydrochloride, For non-agitated solutions, suggested procedures. If a and hydroxylamine hydrochloride have been tried from 17 to 22 hours were remethod required more than 1 under similar conditions and found to be unsatisfactory. quired, and then one could not hour, t h e r e was nothing be sure of the complete regained over the present volumetric analysis now used ( 5 ) . moval of cobalt. A current density of 0.3 amp. per sq. dm. The object of this work has been to develop a rapid electro- was maintained and the electrodes were kept about 2 cm. lytic determination of cobalt. apart. For the following experiments, Belgium cobalt was reResults could not be reproduced using this electrolytic purified by conversion to the chloropentamine cobalt chloride, solution; modifying it by adding varying amounts of sodium dried and ignited to oxide, and reduced to metal by hydrogen- bisulfite, acetic acid, formic acid, and oxalic acid did not firing. The purity of the final product was determined by improve results. Therefore, after about one hundred deterconversion to sulfate and ignition a t 550’ C. until constant minations the method was given UT) entirelv. weight had been obtained. The results thus obtained checked Rotating Anode with the theoretical. A rotating anode has long been used for rapid electrolysis Stationary Electrodes and was suggested and used for cobalt determinations by If stationary electrodes are used, two methods may be Smith and Kollock (S),Exner (W), Brenner and Ross ( I ) , adopted. I n one the solution may be stirred; in the other and Wagenman (4). the electrolysis may be carried out in non-agitated solutions. The apparatus used consisted of a rotating platinum anode and a platinum-rhodium gauze cathode. Attempts were Electrolytic Solution made to reproduce the highly satisfactory results obtained by 10 grams of (NH4)2S04 Smith and co-workers, but these attempts were unsuccessful. 75 to 100 ml. of NHIOH The deposits a t times were very satisfactory and checked with Total volume, 100 ml. the theoretical amounts of cobalt, but all the cobalt had not 1 Received April 15, 1931. Presented before the Division of Physical been removed from the solution. If complete deposition and Inorganic Chemistry at the 81st Meeting of the American Chemical of cobalt were obtained, then the results were too high. Society, Indianapolis, Ind , March 30 to April 3, 1931.
T
I
ANALYTICAL EDITION
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Hydrazine Sulfate Electrolytic Solution 30 ml. of NH40H 5 grams NH4Cl 1 gram of NH2H2N.H&O4 or HCI
Volume, 135 ml. CDIOO, 3 to 6 amp. This electrolytic solution was suggested by Wagenman, and looked very promising since the cobalt could be completely removed in 40 minutes. Results were always high to the extent of about 1 mg. The deposits looked quite fair. A second lot of hydrazine sulfate had to be used, and this proved to be very unsatisfactory, with very black deposits and results which were always high. At the suggestion of Doctor Fuess, Eastman Kodak Company, a small amount of gelatin was added to the new material, This amount was varied from 0.1 to 0.01 mg., and it did improve the character of the deposits, but the results were still 1mg. high. Varying the amount of hydrazine, or gelatin, and boiling the gelatin with the reducing agent failed to give satisfactory results. The method was finally abandoned. Hydroxylamine Hydrochloride 1 gram of KzSOa 40 ml. of NH40H 0 . 3 gram of NH20H. HCI Volume, 100 ml. CD~OO, 4 to 7 amp.
This electrolytic solution was suggested by K. Dengg, formerly of the Ontario Cobalt Works (private communication to the author from H. 13. Willard, University of Michigan). It proved unsatisfactory. No improvement in results was obtained by varying the amount of hydroxylamine, changing the sulfate solutions to chlorides, or adding a small amount of gelatin. The deposits were always black, powdery, and too high, and very seldom was all the cobalt removed in 1 hour. Recommended Procedure
The most satisfactory electrolytic solution tried contained sodium bisulfite. This had been recommended for cobalt depositions, but has always carried with it the objection that sulfur is occluded in the deposits. Such procedures have called for the use of sulfate solutions and 1 to 2 grams of bisulfite. It seemed reasonable that if the amount of bisulfite and the time for electrolysis could be reduced, the error due to sulfur occlusion might be reduced to a negligible quantity or completely eliminated. With this in mind, experiments were carried out with electrolytic solutions of varying compositions, and the following one was finally adopted: Sodium Bisulfite Electrolytic Solution 50 ml. of NH40H 5 grams of NH&I 0 . 3 to 0.4 gram of NaHSOs Volume, 80 to 100 ml. 800 to 1000 r. p. m. CD,oo, 4 to 7 amp.
Time,
hour The electrolyses were made in the solutions as soon as prepared. The bisulfite must be added to the alkaline solution. For amounts of cobalt from 100 to 160 mg., 0.3 gram of sodium bisulfite was needed. Less reducing agent gave streaked deposits and all the cobalt could not be removed in a half hour. For amounts of cobalt less than 100 mg.that is, 80 mg. to 15 mg.-more bisulfite had to be used (0.4 gram) in order to get complete deposition in 30 minutes. Just why more reducing agent must be used with smaller amounts of cobalt is not quite clear, and until the function of the bisulfite is known, such a question cannot be answered. If the solution was not colorless in 20 minutes, 10 to 20 mg. 1/2
Vol. 3, KO. 4
more of bisulfite were added. I n no case was it necessary to add 0.5 gram of reducing agent. The rate of stirring is very important. If this falls below 800 r. p. m., deposits are darker and the electrolysis must be continued for more than a half hour. Such deposits always carry sulfur, and enough to give high results. The addition of 0.1 to 0.5 mg. of gelatin to the electrolytic solution seemed to have a beneficial effect with small amounts of cobalt (80 to 15 mg.). The deposits had a better appearance and qualitatively carried less sulfur, although there is no difference in the quantitative results given in Table I. of Addition of Gelatin t o S m a l l Amount8 of Cobalt SULFUR IN GELATINCOBALT ADDED COBALTFOUND ERROR DEFOSIT Ma. MR. MR. MR. 0.i 12:9 12: 5 +0:4 Trace 17.6 None +0.2 0.5 17.4 31.5 Trace 0.5 31.3 4-0.2 0.1 50.0 50.2 +0.2 Trace None Trace 59.2 5.9 +O. 2 61.4 -0.2 None 61.6 0.5 71.3 71.4 ‘None None 10.1 74.5 None -0.2 Trace 74.7 80.7 00 None 80.7 0.5 82.3 82.3 None 00 Present 83.4 83.7 $0.3 Present 0.5 81.0 80.9 -0.1 Present 0.5 87.0 $0.1 0.5 86.9 Trace Present 87.9 0.1 88.1 -0.2 100.4 None None 100.1 +0.3 108.6 None None 108.7 -0.1 111.9 None Trace 111.6 $0.3 None -0.2 125.5 Trace 125.7 -0.7 133.3 None 134.0 None 162.0 None None 161.7 4-0.3
Table I-Effect
After removing the deposit with dilute nitric acid and then boiling off most of the acid, the solutions were tested for sulfate with barium chloride. Complete removal of cobalt was assured by testing with phenylthiohydantoic acid ( 5 ) The cathode tends to increase in weight. This was found to be owing to deposition of platinum dissolved from the anode, an error which can be taken care of by using the weight of the cathode after the cobalt has been removed for the calculations of results for that particular experiment. The increase in weight amounted to 0.2 mg. unless the electrolysis had been prolonged for three-quarters to one hour, when there was an increase of 0.5 mg. It had been suggested that better deposits could be obtained by immersing the electrodes in the solution when the current was aIready on. This point was carefully tested and it was found that there was no difference in results if the electrodes were placed in the solution either before or after the current was applied. Cobalt must be separated from any obviously interfering elements before electrodeposition. For this purpose, known amounts of cobalt were added to varying amounts of iron, and the cobalt precipitated with phenylthiohydantoic acid (6). The precipitate was washed and dried, ignited to oxide, and dissolved in concentrated hydrochloric acid. It may be dissolved in aqua regia and evaporated with concentrated sulfuric acid, although this process is less rapid. Potassium bisulfate fusions are not to be recommended, since the presence of sulfate necessitates a longer time for electrolysis. The last traces of iron must be removed by a double ammonium hydroxide precipitation. Table 11-Separation I R O N AS
of Cobalt from Interfering Elements Using Iron SULFUR IN
Fe(N0s)a COBALT ADDED COBALT FOUND ERROR DEPOSIT M.9. Mg Mg. Mg. 22.1 4-0.1 None 2 2 . 0 50 20.5 00 None 20.5 50 27.1 +0.1 None 27.0a 100 21.4 00 None 21.4a 500 23.5 +0.2 None 23.3 500 23.7 f0.2 Trace 23.5a 1000 24.1 t0.3 None 23.Sa 1000 22.5 00 None 22.5a 1000 =Phenylthio precipitate dissolved in hydrochloric plus nitric acids. For others ignited oxide dissolved in concentrated hydrochloric acid.
For the determination of cobalt in tungstten carbides, either the tungsten can be precipitated by conversion to tungsten
INDUSTRIAL AND ENGINEERING CHEMISTRY
October 15, 1931
oxide or, if only the percentage of cobalt is desired, the cobalt may be precipitated directly with phenylthiohydantoic acid (6) and the electrolysis carried out as described in the discussion. Tools intended to contain from 13 to 14 per cent cobalt were found to have 13.81 and 13.83 per cent cobalt. Acknowledgment The author wishes to acknowledge the cooperation of Charles Van Brunt and Margaret 0. St. Louis of this depart-
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ment; also Roger L. Jones, of Syracuse University, who spent last summer in this laboratory. Literature Cited (1) Brenner and Ross, J . Am. Chem. Soc., 33,493 (1911). (2) Exner, Ibid., 26, 896 (1903). (3) Smith and Kollock, Ibid., 26,1595. 1606 (1904); a7, 1255 (1905). ~B ~18, t ~ 447 ,~ (1921). l ~ (4) Wagenman, ~ (5) Willard and Hall, J . Am. Chem. SOL,44,2219 (1922).
A Test for Aldehydes Using Dimethylcyclohexanedione' Woltor Weinberger THEMENNENCOMPANY, NEWARK, N. J.
IIIS valuable test, since its introduction by Vorlander in 1896 (5,Y),has been neglected by and is still unknown to the majority of chemists. Of late it has been infrequently used in work in photosynthesis and in detecting traces of aldehydes in biological material, but it has never received the place it deserves as a routine and definite test for aldehydes. There are several distinct advantages inherent in this test: (1) reliability; (2) sensitivity; (3) definiteness (it yields a crystalline precipitate); (4) simplicity of technic; (5) a reagent which does not react with ketones; and (6) which can often be used when other better known reagents cannot give the information sought. Its chief disadvantage, formerly, was that the reagent was not readily available. It may now be purchased easily from the Eastman Kodak Company, Rochester, N. Y. The reagent is dimethylcyclohexanedione, commonly called dimetol and dimethylhydroresorcin. It unites with aldehydes, the condensation product so formed being soluble in water with difficulty. The result of work undertaken to determine how this reagent might best be used, its defects, and its sensitivity, is here presented. The melting points of a number of derivatives are also included. The original experiments were performed with formaldehyde. Subsequent experiments, however, show that the method adopted and the conditions and cautions laid down here apply equally well to other aldehydes. The reagent is soluble in alcohol and water. It oxidizes slowly in the presence of air, and when kept in well-stoppered bottles keeps indefinitely (6). Test Procedure
T
The solution of the reagent is added to the solution of the aldehyde. Under proper conditions the condensation product separates out of the solution as a fine crystalline and exceedingly insoluble precipitate. The oxygen of one molecule of formaldehyde unites with a hydrogen atom of each of two molecules of the reagent, water splitting off, and the residue is the insoluble compound (4, 5; 7 ) . Let us assume for the sake of simplicity that the reagent is dihydroresorcin 0
0
II
HzC@
+
C=O
HIC
O=C
Received May 26, 1931.
CHI CH2
HzC
Method for Precipitation of Aldehydes The method decided upon for the precipitation of aldehydes by dimetol is as follows: A 5 to 10 per cent alcoholic solution of the reagent is prepared. Sodium chloride is added to the aqueous solution of the
aldehyde. The aqueous solution containing the aldehyde is neutralized and left neutral or very faintly acid-e. g., with dilute acetic acid-and cooled. To this cold solution a few drops of the reagent are added. The solution is then vigorously stirred, or permitted to stand until the precipitate takes its final crystalline form.
0
CII H HC! R CI H O F K ( ) C H + H ~ C u i \ & o H 2
CH2 1
0
I1
This condensation product is soluble in hot water, alcohol ether, petrolic ether, gasoline, acetone, and, very probably, in most organic solvents. It is essential as a first condition, then, that the aldehyde be precipitated from a cold aqueous solution, although small amounts of alcohol do not interfere. It may be noted here that the condensation can take place in an alcoholic solution and the condensation product precipitated by the addition of water. These solubilities in hot water and in alcohol are put to good use in purifying the crystals for melting-point determinations. The condensation product is easily soluble in fixed and carbonate alkalies and in acids, but it is not appreciably soluble in cold, very dilute solutions of organic acids. The reagent should, therefore, be added to a neutral solution of the aldehyde. Since this is impracticable, the solution of the aldehyde should be made faintly acid with some weak organic acid. A saturated aqueous solution of the condensation product formed by the reaction of formaldehyde and dimetol contains a t 19" C. 0.0005 gram per 100 ml. (6), and much less than that in the presence of excess dimetol. The condensation product is still less soluble in the presence of salt. The addition of sodium chloride was resorted to in order to increase the sensitivity of the test. The precipitate does not come immediately, but comes down slowly, becomes bulkier on standing, and then takes its final crystalline form. The formation of the precipitate and its crystallization is materially hastened by vigorous stirring. This precipitate shows a characteristic structure under the microscope (5).
'2x0 O=C CHr
CHz
CHz
The precipitate may be recrystallized from a suitable solvent (for example, alcohol or hot water), and its melting point determined. By means of this determination the presence of a specific aldehyde may be confirmed. A number of melting points for dimetolaldehyde derivatives and their sources are given in Table I.
