4
382
INDUSTRIAL AND ENGINEERING CHEMISTRY
loss in copper sometimes amounted to more than 2 mg. In one experiment, the reagent was allowed t o act upon a mixture of 0.4 gram of cupric oxide, 0.3 gram of cuprous oxide, and 0.1 gram of copper for 1 hour. At the end of this time, 0.0050 mg. of copper had dissolved. Care must be taken not to allow the extraction solution to become saturated with carbon dioxide. If the gas inlet to the flask be placed beneath the surface of the liquid, solubility errors will be increased. Fifteen determinations of metallic copper made upon a sample of electrolytic cuprous oxide indicated a n average value of 0.25 per cent, with a maximum deviation of 0.01 per cent and an average deviation of 10.006 per cent. The same number of determinations on a sample of “thermal process” cuprous oxide yielded an average value of 1.07 per
VOL. 8, NO. 5
cent, with a maximum deviation of 0.02 per cent and an average deviation of h0.008 per cent.
Literature Cited (1) Am. SOC. Testing Materials, Standard Method of Routine Analysis of Dry Cuprous Oxide, D-283-33. ( 2 ) Ibid., Standard Specifications for the Toxic Ingredients in AntiFouling Points, D-277-31. (3) Bonner, W. D., and Kaura, B. D., IWD. E m . CHEX, 19, 1288 (1927). (4) Geilmann, W., and Weibke, F., 2. anorg. allgem. Chem., 199, 120 (1931). (5) Le Blanc, M., and Sachse, H., Ann. Physik, 11, 727 (1931). (6) Scott, W., “Standard Methods of Analysis,” 4th ed., p. 208, New York, D. Van Nostrand Co., 1927. (7) U. S. Navy Department Specifications, 52 C4b, 1935.
RECEIVED August 20, 1936.
Quantitative Determination of Cadmium and Lead in Zinc Using a Grating Spectrograph with a Sector Disk HARRIS M. SULLIVAN, The Pennsylvania State College, State College, Pa.
T
HIS work was a n attempt to determine the possibility of using a replica grating spectrograph for making a quantitative determination of metallic impurities in compounds. The specific problem a t hand was the quantitative determination of cadmium and lead impurities in zinc. It was desired to take a specimen of unknown content and, by a simple procedure requiring approximately 15 minutes, excite the spectrum of the specimen, obtain a spectrogram, and from this spectrogram obtain the quantity of the impurities present. A method suitable for commercial use was desired. The grating is mounted in the Rowland fashion, with the camera fixed t o photograph the first order of the visible range. It is posqihle, by rotating the grating about its vertical axis, to obtain wave lengths from 10,000 A. to 2100 A,, the ultraviolet just outside the visible range being the most useful. The logarithmic sector disk is placed as near the slit as possible, and the mounting made stigmatic by placing the arc at the focal center of a convex lens, thus rendering a parallel beam of light on the slit. The sector disk is caused to rotate at a speed of 300 r. p. m. and is adjusted so that approximately 3-mm. length of the 16-mm. slit is left open at all times. The remainder of the slit opening is varied during the time of exposure as the sector disk rotates in front of it. The variation of time along the slit causes the lengths of the lines on the film t o vary according t o the intenaity of the line.
FIGURE1. SPECTROGRAM
A typical spectrogram is shown in Figure 1. Assuming the percentage content of the element present to be directly proportional t o the intensity of its characteristic lines for small percentages and the blackening of the film to vary logarithmically with the intensity falling upon the film, then the lengths of the lines produced by different percentages of a n element plotted against the percentage of the element should result in a curve which is a straight line. The curves were actually found to vary slightly from straight lines, as seen in Figure 2 . The arc consists of two vertical graphite electrodes, which must be of the purest graphite and approximately 0.6 cm. (0.25 inch) in diameter. The lower (positive) electrode is drilled with a 0.39-em. (0.156-inch) drill to a depth of 0.6 cm. (0.25 inch) and the sample under investigation is stuffed into this basin. This method of excitation of the spectra of slowly volatilizing substances is very effective because of the high temperature reached by the carbon arc. The current through the arc was about 5 amperes and the voltage supply 220 volts direct current. The voltage drop across the arc was 40 volts and the arc gap 1 cm.
It is essential in this type of work that the current and voltage drop across the arc, and consequently the energy consumed by the arc, remain constant. An inductance may be placed in series with the arc and resistance t o stabilize the arc c u r r e n t . Any other proved method of arc excitation of the spectra of the elements should prove as satisfactory as the one used here. Because sulfates are stable in the arc, the sulfate form of the sample was used for these tests. Any metal sample may be put into the sulfate form by first dissolving the sample in concentrated nitric acid, then adding concentrated sulfuric acid and evaporating the solution to dryness under a hood. After the residue has comdetelv dried. it i s g r o u n d i n m o i t a r and
ANALYTICAL EDITION
SEPTEMBER 15, 1936
mixed thoroughly. I n this work, samples were prepared from chemically pure zinc sulfate, lead sulfate, and cadmium sulfate. These were thoroughly dried, weighed out in known amounts to obtain the desired percentages, then ground and mixed in an agate mortar. Percentages are expressed in terms of weight per cent of zinc, lead, and cadmium metal present rather than in terms of total weights of salts present. Several technics of preparing the sample for its spectra excitation have been reported ( I , $ , 3). I n this experiment the one chosen was that of placing the same amount of powdered specimen in the lower electrode basin and burning the arc for a definite period. This time of exposure was 1 minute. The films were developed for 1 minute a t about 25’ C. The lines were measured with a small millimeter scale and magnifying glass in diffused white light. Measurements of lengths of the spectral lines can be repeated to within 0.2 mm. IMPURITY IN ZINC TABLEI. CADMIUM Length of Line (3261 A.)
Cadmium
%
Mm.
0.001 0.002 0.003 0.007 0.012 0.020
5.1 5.5 5.8 6.8 8.0 9.8
IN ZINC TABLE 11. LEADIMPURITY
Length of Line
Lead
% 0,001 0.002 0.003 0,008 0.012 0.020
(2863
A.)
Mm. ,
..
...
1.8 2.8 3.6 4.9
(2833
A,)
PERCENT IMPURITY FIGURE 2.
7.8 9.0
Table I shows the tabulated results for cadmium, and Table 11, for lead. These results are shown graphically in
CADMIUM AND
LEAD IMPURITIES
IN ZINC
Figure 2. The 2663 8. line of lead fails to appear below 0.003 per cent lead. It can be concluded from these results that cadmium and lead impurities in zinc can be easily detected down to 10 parts in one million, with an accuracy of 10 to 15 per cent. The lengths of the cadmium and lead lines a t 0.001 per cent indicate that percentages of these impurities below 0.001 per cent could be detected and the amounts estimated.
Acknowledgment It is a pleasure to acknowledge the loan of the replica grating spectrograph and accessory apparatus by the Central Scientific Company of Chicago, without which this investigation could not have been carried on.
Mm. 4.4 5.0 5.3 6.8
383
Literature Cited Methods of Chemical Analysis by Emission Spectrum,” London, Adam Hilger, 1932. (2) Slavin, Morris, Ens. Mining J., 134, 509-13 (1933). (3) Twyman, F., and Smith, D. M., Am. Inst. Mining Met. Engrs., Tech. Pub. 79 (1928). ( 1 ) Gerlach and Schweitaer, “Foundations and
RECEIVEDJune 4, 1936. Contribution from the Department of Physics, Dlvislon of Chemical Physics, School of Chemistry and Physics, The Pennsylvania State College.
Determination of Manganese in 18-8 Corrosion-Resisting Steel LOUIS SILVERMMS, 2129 Wightman S t . , Pittsburgh, Pa.
S
TEELS of the 18-8 (chrome-nickel) type dissolve rather
slowly in sulfuric acid, but rapidly in aqua regia. Both the nitric and hydrochloric acids are easily removed by perchloric acid a t its boiling point. After cooling and diluting, the chromium is precipitated during the neutralization with zinc oxide emulsion. After correctly preparing the solution and titrating the manganese, the results on standard samples ran about 0.1 per cent too low. It was possible that a portion of the manganese had separated as a chromate, or that some manganese was oxidized to the trivalent form by the perchloric acid and came out as the hydroxide upon the addition of the zinc oxide emulsion. To take care of either possibility, sulfurous acid was added to the solution which had been fumed with perchloric acid and diluted. Completion of the routine analysis showed exact checks with the sulfuric acid solution method. Weigh 1 gram of drillings into a 150-cc. beaker. Add 25 cc. of the dissolving solution (1000 cc. of water, 250 cc. of nitric acid, and 750 cc. of hydrochloric acid), and heat until solution is complete. Add 10 cc. of perchloric acid (technical), and boil until the chromium is oxidized and the perchloric acid starts to condense on the cover and walls of the beaker. Remove from the hot plate. Wash the acid down with water. Dissolve the residue with water, dilute to about 30 cc., and add 10 cc. of a saturated sulfur dioxide solution (10 cc. of a 25 per cent sodium sulfite solution will do) to reduce the chromium. Boil 2 or 3 minutes. Cool.
Neutralize with freshly prepared zinc oxide emulsion, using but
a slight excess. Cool, and make up the solution to 250 cc. in a
volumetric flask. Empty into a 400-cc. beaker and stir; the chromium will settle in a short time. Pipet out 50 cc. into a 150-cc. fat-extraction flask. Add 30 cc. of a mixture of 3600 cc. of nitric acid, 810 cc. of sulfuric acid, 300 cc. of orthophosphoric acid, 232 grams of silver nitrate, and 13,860 cc. of water. Heat until the solution is clear. Add 20 cc. of 6 per cent ammonium persulfate solution, and heat carefully till bubbles of oxygen form on the surface of the liquid. Cool. Titrate wit,h arsenite solution of such strength that 1 cc. is equivalent to 0.1 per cent of manganese on the 0.2-gram sample. Using U. S. Bureau of Standards sample KA2-S, 5.5 cc. were required by both this and the sulfuric acid solution methods.
Discussion This solution method is faster than solution in sulfuric acid, or directly in perchloric acid. It has the further advantage that iron is not separated from solution by the zinc oxide. Thus the permanganate solution which is brought to the arsenite buret is in almost the same condition as that of a lowchromium steel which was probably used to standardize the original arsenite solution. The accuracy is the same as that of the sulfuric acid solution method. RECEIVED June
11, 1938.
