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countered in igneous rocks. A mixture of 2.5 ml. of 25 per cent sodium hydroxide and 10 ml. of 0.005 per cent pure zinc solution (corresponding to 0.1 per cent of zinc in a 0.5-gram sample) shaken with 1ml. of 0.001 per cent dithizone solution gave a trace of pink color in the carbon tetrachloride layer which was distinctly less than that produced by 0.05 microgram of cadmium. Tin, bismuth, silver, and thallium are also without effect in small amounts. Manganese shows a tendency to prevent the complete extraction of cadmium, but this difficulty is overcome by the addition of hydroxylamine hydrochloride. The element most likely to give trouble is nickel. Nickel dithizonate in carbon tetrachloride solution is partially decomposed by shaking with 0.01 N hydrochloric acid, so that more or less nickel will go into the final solution with cadmium. If more than a very small amount of nickel is present in this solution, it will impart a brown color to the carbon tetrachloride layer, the pink color of cadmium dithizonate is then obscured, and the determination becomes impossible. The solution of this difficulty lies in preventing, as far as possible, the extraction of nickel from the ammoniacal citrate solution.
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If the solution is made barely ammoniacal most of the nickel will remain in the aqueous phase and all, or nearly all, of the cadmium will be extracted. As much as 0.03 or 0.04 per cent of nickel may be present in the sample without causing difficulty if care is taken to avoid an excess of ammonia. Larger amounts of nickel are likely to cause trouble, so that the method given is not applicable to all rock samples. Moreover, large amounts of any metal extracted by dithizone (copper, zinc, etc.) are undesirable, because the complete removal of cadmium from a large volume of carbon tetrachloride phase by shaking with 10 nil. of 0.01 N hydrochloric acid may be difficult. However, in most silicate rocks the quantity of metals extracted by dithizone is small and the method described is adequate.
Literature Cited (1) Fischer, H., and Leopoldi, G., Mikrochim. Acta, 1, 30 (1937). (2) Goldschmidt, V. M., Skrifter Norske Videnskaps-Akad. Oslo I . Mat. Natur. Klasse, 1937, No. 4, p. 32. ( 3 ) Noddack, I., and Noddack, W., Svensk Kern. Tid., 46, 173 (1934). (4) Sandell, E. B., IND. ENG.CHEX.,Anal. Ed., 9, 464 (1937).
Colorimetric Determination of Nickel As Nickel-Ammonia Complex Ion GILBERT H. AYRES AND FRANCENE SMITH Smith College, Northampton, Mass.
THE
rapid development of photoelectric colorimeters and the wide application of colorimetric methods of analysis suggested to the authors the possibility of determining nickel on the basis of the blue color of nickel-ammonia complex ion, the color being measured photoelectrically. Such a method might find some application in steel and ore analysis, being simple and rapid.
Development of the Method APPARATUS AND REAGENTS.In the proposed method the concentration of nickel was indicated by the spectral transmission of blue nickel-ammonia complex ions. The instrument employed in measuring the transmission was the Yoe photoelectric colorimeter (4). Special grades of nickel salts low in cobalt and copper were used; all other reagents were of analytical reagent quality. Stock solutions, one each of nickel chloride, nickel nitrate, and nickel sulfate, were made up to contain approximately 5 mg. of nickel per ml., and were standardized gravimetrically with dimethylglyoxime (1). Suitable dilutions of the stock solutions were used in formulating the calibration curve. EFFECTOF AMMONIACONCEXTRATION. A preliminary study of the variations in transmission by nickel-ammonia ions uith concentration of ammonia was made in order to determine what concentration of ammonia should be used. From the nickel sulfate solution, two series of standards containing varying amounts of ammonia were prepared; one series had a nickel concentration of 200 mg. per liter and the other 2000 mg. per liter. At an ammonia concentration of 1.5 N the solutions were characterized by a blue color and by the complete absence of insoluble basic salt. With increasing concentration of ammonia, the blue complexes gave way
to the violet complexes, the coloration becoming constant a t about 2.5 N ammonia. Since, in the Yoe instrument as used without color filter, the blue solutions absorb more light than do the violet, they provide the more sensitive means for the determination of nickel. The instrument was therefore calibrated for nickel determination on the basis of the color produced in a solution 1.5 N in ammonia. EFFECTOF ANIONS. From the stock solutions of nickel chloride, nickel nitrate, and nickel sulfate, three series of standards were prepared. The ammonia concentration in all cases was 1.5 N , but vithin each series the nickel concentrations varied by convenient intervals. In Figure 1, the plot of values of log R/50 against nickel concentration shows that the system follows Beer’s law only for nickel concentrations up to about 600 mg. per liter. It is obvious that the anion has no influence on the transmission. EFFECTOF AimfoNIUM SALT. Since application of this method of analysis would, in all probability, involve making the determination in the presence of ammonium salt, the effect of this factor was investigated. The samples tested covered a nickel concentration range from 50 to 2000 mg. per liter and ammonium salt concentration up to 3.0 N . The presence of ammonium salt up to 1.5 N had no appreciable effect on the transmission. EFFECT OF TIME. Solutions read a t definite time intervals over a period of 150 hours showed no significant variations of transmission with time. EFFECTOF COBALT. Because of the frequent occurrence of cobalt with nickel, a short study was made of the effects of the presence of cobalt on the colorimetric estimation of nickel. Using standardized solutions of cobalt chloride and nickel chloride, a series of solutions was prepared which contained 500 mg. of nickel per liter and varying concentrations
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complex absorbs the red end of the spectrum and transmits COLORIMETRICALLY AFTER PRECIPI- the shorter wave lengths. Therefore, when cobalt is present TABLE I. NICKELFOUND TATION AS NICKELDIMETHYLGLYOXIME it must be separated unless present in very small, known conNickel Found centration for which compensation can be made in a correNickel Taken Gravimetric Colorimetria from ppt. sponding blank of the same age. Mg./l. R4 Mg./l. R Mg./l.
a
43.5 41.5 39.4 36.2 33.6 30.0 27.6 23.6 In the tables, R designates colorimeter reading
43.3 41.0 39.4 36.3 33.5 30.3 27.3 23.2 in microamperes
of cobalt in 1.5 N ammonia. Colorimetric readings were made on these solutions a t various time intervals. At a cobalt concentration of 50 mg. per liter the blue color representing 500 mg. of nickel per liter was completely obscured by a light brown. Above this concentration of cobalt, the brown color of the solutions increased. After standing approximately 12 hours, the brown color had changed to pink or red, depending upon the concentration of cobalt, and the transmission was still changing after 28 days. The data are represented graphically in Figure 2. The interference by cobalt could not be eliminated by use of a filter in the instrument. Spectroscopic examination of solutions containing the cobalt-ammonia complex showed that they absorb all wave lengths of the visible spectrum except those in the red; on the other hand, the nickel-ammonia LOR
\I I I .I
DETERMINATION OF NICKELIN STEEL TABLE11. COLORIMETRIC AFTER SEPARATION OF NICKEL WITH DIMETHYLGLYOXIME (Volume of solution for colorimetric reading, 100.0 ml.) Sample Weight -ColorimetricGravimetric Grams R Mg./l. % % 3.18 477 1.501 31.0 480 3.20 1.501 30.9 480 3.20 1.502 30.9 493 3.29 . 1.501 30.5 493 3.29 1.501 30.5 504 3.36 1.501 30.2 501 3.33 1.501 30.3 497 3.31 1,500 30.4 477 3.18 31.0 1.501 3.33 501 1.501 30.3 Av. 3.27 3.290
Applications of t h e Method The determination of nickel colorimetrically as nickelammonia complex ion requires the absence of other substances which yield precipitates or colored solutions with ammonia. Since the systematic separation of these interfering constituents is rather laborious, it seemed Dossible that the well-known quantitative seiaration of nickel from such ions by dimethylglyoxime in the presence of tartrate, with subsequent decomposition of the nickel dimethylglyoxime thus produced, would provide a means whereby the nickel could be more conveniently isolated in solution suitable for colorimetric determination. DETERMINATION AFTER SEPARATION AS NICKEL DIMETHYLGLYOXIME. In order to test the method proposed above, a series of standard nickel solutions of varying concentrations m s read colorimetrically as nickel-ammonia complex. The nickel in a definite volume of each sample was precipitated with dimethylglyoxime, the precipitate being received in a filtering crucible with fused-in fritted-glass filter disk; t o serve as a check on the colorimetric analysis, the nickel dimethylglyoxime precipitate was dried and weighed. This precipitate was then dissolved from the filtering crucible by means of a small amount of concentrated nitric acid, and the acid solution and washings were evaporated to a volume of a few drops. The solution was transferred t o a volumetric flask, made up to volume so as to be 1.5 N in ammonia, and then read in the colorimeter. Blanks prepared from dimethylglyoxime by nitric acid treatment as above gave the same readings as ammonia blanks, indicating the absence of interfering agents in the solution. The results are shown in Table I. In another series of 7 solutions, each containing 496 mg. of nickel, the nickel found by the above method was 506, 500, 486, 500, 500, 500, and 500 mg.; average, 499 mg. Samples of nickel steel were analyzed colorimetrically from the nickel dimethylglyoxime precipitate. To serve as a check, these precipi\ tates were dried and weighed before being prepared for colorimetric reading. Results are shown in Table 11.
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it has been the experience of the authors that by the colorimetric procedure a result on the analysis of three to five samples can be obtained in about one half the time required by the gravimetric procedure. The authors are cognizant of the fact that the method proposed requires the cons t a n t a t t e n t i o n of the analyst during this time, whereas the gravimetric procedure does not. The nickel dimethylglyoxime precipitate can be decomposed with concentrated h y d r o c h l o r i c acid to give a satisfactory solution for analysis as nickel-ammonia complex, but more difficulty is experienced in dissolving the precipitate from CONCENTRATION OF COBALT, MG. PER LITER the filter plate with hydrochloric acid than with nitric acid. Sulfuric acid was found to be unsatisfactory, for Discussion of Results during the evaporation of the acid solution there was formed a Using the method proposed, the color of nickel-ammonia yellow-green precipitate which was difficultly soluble in water complex ions is a satisfactory basis for the estimation of and ammonia. In the use of nitric acid, if evaporation be nickel. The color system is stable. A concentration of 1.5 N carried to the separation of solids, the residue is not readily ammonia is satisfactory. The presence of ammonium salt soluble in water or ammonia. This difficulty can be overaffects only slightly the transmission of the solutions. Idencome by a second treatment with a small amount of nitric tical transmissions were obtained in ammoniacal solutions acid, the evaporation being stopped before solids separate. made from the chloride, nitrate, and sulfate of nickel. During the process of calibration of the instrument, and Measurements have been made up to a nickel concentrain the subsequent applications of the method, an occasional tion of 4000 mg. per liter. As little as 5 mg. per liter can be sample showed a slight turbidity, and most of the samples, detected with certainty. The region of highest sensitivity lies including the blank solutions, which were clear by naked-eye between 500 and 1500 mg. per liter, for in this range the perobservation were seen to scatter light somewhat when placed centage deviation due to the instrument error (0.2 microin the light beam of the instrument. This turbidity could ampere) is a t a minimum; within this range the method is usually be removed by filtration and as a matter of routine in accurate to 1 per cent. This method, therefore, compares preparing solutions for colorimetric reading they were filtered favorably in accuracy with other colorimetric methods for through Whatman paper No. 50. Traces of any residue left nickel (2, S ) , in which the accuracies range usually from 1 on the filter gave negative tests for nickel. to 5 per cent. Although the intensity of the blue color of nickel-ammonia complex ions is not sufficient to permit visual matching with any degree of accuracy, if the transmission is Summary measured photoelectrically the method is as satisfactory as A method has been developed for the colorimetric estimaother colorimetric methods performed visually. tion of nickel as its ammonia complex. The color of the comThe colorimetric method with ammonia is subject to esplex is stable, and is very little influenced by added ammosentially the same interfering ions as other colorimetric nium salt. methods for nickel. The separation of nickel from interfering The method has been applied to the analysis of nickel in a constituents by precipitation with dimethylglyoxime, followed steel by utilizing dimethylglyoxime to separate the nickel, by transposition to nickel-ammonia complex ion for colorifollowed by conversion of the precipitate to nickel-ammonia metric estimation, can be accomplished much more simply complex ions for colorimetric determination. and rapidly than the removal of interfering ions by precipitations with hydrogen sulfide, ammonia, etc., as required in the thiocarbonate and the dithiooxalate methods. Literature Cited The use of dimethylglyoxime for accomplishing the separa(1) Kolthoff, I. M., and Sandell, E. B., “Textbook of Quantitative tion of nickel, followed by decomposition of the precipitate Inorganic Analysis”, pp. 684-5, New York, Macmillan Co., with nitric acid and the colorimetric measurement of nickel 1936. as its ammonia complex, has been applied successfully to the (2) Snell, F. D., and Snell, C. T., “Colorimetric Methods of Analyanalysis of nickel steel. Although the precision is not high, sis”, Vol. I, pp. 313-20, New York, D. Van Nostrand Co., 1936. the average of several determinations agrees well with the (3) Yoe, J. H., “Photometric Chemical Analysis”, Vol. I, pp. 295average of the gravimetric determinations. From the point 305. New York. John Wilev & Sons. 1928. a t which the nickel dimethylglyoxime precipitate is filtered, (4) Yoe, J. H., and Crurnpler, T: B., IND:ENQ.CHEY., Anal. Ed., the colorimetric method is more rapid than the gravimetric; 7, 281 (1935).
