Solution Method for Spectrographic Analysis Utilizing a Dropping Electrode R . J. KEIRS
AUD
D. T. ESGLIS, University of Illinois, Urbana, 111.
T
maximum opening. (These specifications are for use only when the tube is filled to a point below the stopcock level-i. e., in use, the glass tube is never filled to include liquid in the stopcock. Filling the tube past the stopcock should be avoided, since the rate of floiv cannot be easily duplicated.) If larger volumes of solution are needed for excitation, the tube should be made of greater length or greater diameter. Since corrosive liquids are somet'imes employed, it is necessary to shield the electrode stand, etc., from the spray which the spark produces during excitation. A most satisfactory and inexpensive form of shield can be made from a piece of absorbing paper (Bluebird lining paper), cut and folded into a box, with an open end and top, and of such dimensions that it cttn he fitted between the electrode holders. A small slot is cut in the bottom of the shield to allon- the lower electrode to protrudc.
HERE often arises in spectrographic analysis a need for
a simple, yet reliable, method for the quantitative tleterniination of substances in solution. Procedures for the preparation of standard pomder samples for spectrographic work and their subsequent analysis are generally inore laborious antl time-consuming than those utilizing solution$. Ailso,the homogeneity of standard solutions is niuch more certain and their preparation is simpler than those for either powders or metallurgical specimens. Several methotls for solution anal> have been described in the literature. Each has its individual merits ant1 dieadvantages as to ease of manipulation, complexity of design of container for the solution, adaptability to ayailable electrode stand design, reproducibility of excitation conditions, and quantity of solution needed for an analysis. The forms of apparatus described by Gerlach and Schw5tzer ( I ) , T~vyinaii and Hitchens (j), and Jolihois antl Bossuet ( 2 ) employ special electrode equipment arid relatively large quantities of solution. Of several types of electrodes described in the literature, one attributed to Secke is nientioned by L o w (5') and it has mine similarity to the method proposed in the present paper. However, no data are given by L o w to show the reliability of the apparatus in quantitative work, and the original communication coiild not be located. Aft'er completion of the work of this paper, it was found t'hat,L3.indegardh (4) also refers to the work of Secke and has suggest'ed changes in proceclure analogous to those employed here. The technique, which in the present work was designed for use with a cold, high-potential spark, involves a slow ant1 regulated addition of the solution through a hollow upper electrntle. Y
Operation After the spect,rograph has been adjusted and the plate holder loaded, the carbon electrodes are placed in the electrode stands, with the usual precautions as to electrode heights and spark gap distances. The drilled carbon serves as the top electrode, while the flat-surface carbon serves as the bottom electrode. The dropping electrode is then inserted firmly into the top carbon electrode (no other support being necessary to hold it), the absorbing paper splash-shield is placed about the electrodes, the stopcock is opened, and the spark is started immediately. Observation of the time is noted the instant the spark is excited, and a preliminary sparking of 15 seconds is given the electrodes (solution flowing) before the shutt,er of the spectrograph is opened. After the 1.5 seconds' preliminary sparking, the shutter is opened, and the exposure is continued for 60 seconds. (The spark is not interrupted between the preliminary sparking and the time the shutter is opened.) The shutter is then closed, the spark discontinued, and the stopcock closed in the order given. The dropping electrode is removed, drained, cleaned, rinsed with the next solution to be run, and finally filled. Sew or repurified carbon electrodes are placed in the stand, and the procedure is repeated until all desired solutions have been examined. To facilitate draining of the tube when cleaning and refilling, the capillary tube is inserted in a suction flask, equipped with a onehole rubber stopper. After the spectra have been taken, the plate is developed, fixed, washed, and dried, and the desired line densities are determined. Here, as in all quantitative spectrographic analysis, standardization and duplication of technique are of utmost importance. The dropping electrode is easily cleaned and filled by attaching a small piece of rubber tubing to the upper end and connecting to a vacuum line. The solution to be analyzed is sucked into the tube to a mark belon- the stopcock, the vacuuni line is removed, the stopcock is closed, and the tube is removed from stock solution and n-iped dry. The rate of flon- from the dropping electrod? is governed bythe size of t h e capillary orifice. This arrangement allow the solution to flo\v continuously and evenly into thr spark, where a fresh eurface is constantly being formed, and tiit, excess is expelled from the electrodes by the force ~f the spar high-potential (cold) spark muht bra wed for excitation, since t h r direct current arc develops too high a temperature, which affects the delivery of the solution through the capillary orifice and a t times n-ould he sufficient1)- hot to melt the gl
Electrode S?-stem The lower electrode is an ordinary spectroscopic carbon rod \r.ith a flat end surface exposed to the spark. The upper carbon electrode is constructed, as shovn in B (Figure l ) , from a piece of 0.25-inch (6.35-mni.) spectroscopic carbon rod 1.26 inches (31.8 mm.) long. One end of the electrode is drilled to a depth of 1 inch (25.4 mm.) with a 0.11-inch (2.78-mm.) drill. (The size and depth of drill were chosen to fit the particular size to which the glass capillary end TYBS drawn.) The remaining 0.25 inch of the electrode is drilled 11-ith a 0.08-inch (1.98-mm.) drill. The smaller hole is necessary to effect a steady flax- of solution into the spark and to prevent large drops from playing upon the spark and varying excitation conditions. The device for introducing the solution, a "dropping electrode", ia cwnstructed from a piece of glass tubing 0.25 inch (6.35 mm.) i n diameter, 7 inches (17.8 cm.) long, and fitted with a stopcock at one end, as shown in A (Figure 1). The other end is softened in a flame and drawn to a pointed capillary. The capillary tip is then fire-polished until the orifice will permit a flow of approximately 0.9 cr. per minute, a-hen the stopcock is adjusted to the
Espeririien tal Standard solutions of inangaiiese were prepared of the following manganese concentrations: 0.5, 0.25, 0.10, 0.05, 0.025, and 0.01 nig. per ml. The solyeat used was 4.5 per cent. liydrocliloric acid. Copper was chosen as the internal standard. aiitl a solution of cupric sulfate was prepared, of such coriceiitratioii ai to gigr satisfactory line densities for the line a t 2369.8 -1. The solutions actually used in the I were prepared by mixing equal T-oliimes of manganese and cupric sulfate solutions. 275
INDUSTRIAL AND ENGINEERING CHEMISTRY
276
READINGS OF MANGANESE AND COPPER LINES TABLE I. DENSITOMETER Mn Plate 1 Conon. M n Cu
Plate 2 hln Cu
Plate 3 hXn Cu
46.7 41.8 30.3 23.6 15.9 6.7
42.2 37.0 28.1 19.8 12.6 6.2
Plate 4 Iln Cu
Plate 5 hln Cu
Plate 6 Mn Cu
Mg./cc. 0.5 0.25 0.10 0.05 0.025 0.01
46.9 39.6 30.4 23.1 15.5 8.1
23.6 22.0 23.6 24.9 23.6 24.0
23.1 24.1 23.7 23.0 23.2 23.2
21.1 42.2 2 0 . 0 42.0 2 0 . 8 2 1 . 2 3 6 . 2 2 0 . 0 3 6 . 1 21.1 22.1 26.5 20.3 27.5 21.3 20.3 19.3 21.2 18.6 20.4 21.0 13.1 21.2 13.7 21.8 21.6 6.522.5 6.521.5
LINETO TABLE 11. RATIOOF DENSITIESOF MANGANESE COPPERLINE A?.
Mean DeviaPlate Plate Plate Plate Plate Plate Aver- Devia- tion of Concn. 1 2 3 4 5 6 age tion Mean
Mn
Mg./cc. 1.99 2.02 2.00 2 . 1 1 2.02 2.08 2 . 0 3 0.036 0.014 0.5 0.25 1.80 1.73 0.10 1.29 1 . 2 8 0.05 0.93 1.02 0 . 0 2 5 0.66 0 . 6 8 0.01 0.34 0.29
1.74 1.81 1.27 1.31 0.98 0.91 0.60 0.62 0.29 0.29
1.71 1.29 0.91 0.63 0.30
1.74 1.42 0.96 0.68 0.34
1.75 1.31 0.96 0.64 0.31
0.031 0.036 0.035 0.030 0.021
0.012 0.014 0.014 0.012 0 0086
17.1 21.7 20.0 22.9 22.8 24.0
35.7 37.7 28.5 22.1 15.6 8.1
VOL. 12, NO. 5
The lines chosen were free of any background, so that no correction was necessarv. The ratio of the density of the manganese line to the copper line was plotted against log concentrac:nm Y’”lL*
Table I gives densitomete: readings of the manganese line at 2576’12 and the copper line a t 2369.8 =1. for different manganese concentrations. Six separate plates were exposed, using the same standard manganese solutions. Table I1 gives the ratio of the densities of the manganese line to the copper line, the average ratio value, mean deviation, and average deviation of the mean. When the average ratio values are plotted against the log-concentration (mg. of manganese per cc.), a curve is obtained, as shown in Figure 2.
Literature Cited
The electrodes were placed a t a distance of 60 cm. from the slit of the spectrograph. The spark gap was adjusted to 6 mm., and duplication of the gap distance was accomplished by the use of a glass spacer 6 mm. thick. No external condensing lens was used. A Bausch & Lomb large Littrow (quartz) spectrograph was employed, using a slit width of 70 microns and 4-mm. height. Prism position 7, covering the range 2300 t o 2900 A., was used to register the section of spectrum which contained the manganese and the copper lines selected.
(1) Gerlaoh, W., and Schweitzer, F., 2.anorg. allgem. Chem., 195, 255 (1931). (2) Jolibois, P., and Bossuet, R., Compt. rend., 204, 1189 (1937). (3) Lowe, Fritz, “Optisohe Messungen des Chemikers und Mediziners”, 2nd ed., pp. 53-7, Dresden and Leipzig, Verlag von Theodor Steinkopff, 1933. (4) Lundegardh, H., “Quantitative Speotralanalyse der Elemente”, p. 96, Jena, Verlag von Gustav Fischer, 1929. (5) Twyman and Hitchens, Proc. Roy. Soc., -4133,72-92 (1931).
Dry Ice as a Preventive of Atmospheric Oxidation GEORGE E. FERGUSON AND LEOPOLD SCHEFLAN Pyrene Manufacturing Company, Newark, N. J.
I
T IS well known that tin in commercial tin-lead solders
can be determined accurately by titration with standard iodine solution, provided that it is present entirely as stannous ion in hydrochloric acid solution (1). The use of solid carbon dioxide has been found helpful in preventing oxidation of the stannous ion previous to the titration.
I
2.0
2.2
1.4
P.6
%2
70
i2
I i.4
i.6
LOG CONCENTRATiON
FIGURE 2 Excitation of the sample was obtained by a high-potential spark supplied from a 220-volt source, with sufficient resistance to produce a current of 17.5 amperes in the primary of a 1000 to 1 5-kw. transformer. The secondary circuit conmicrofarad sisted of 8 condensers (in parallel) of 815 X each. No inductance coil was used in the secondary circuit. The solutions were analyzed by the technique already described, and the spectra were recorded on Eastman D. C. (double-coated) orthochromatic plates. The plates were processed using Eastman standard x-ray developer and fixer, and were developed for 5 minutes a t 18” C. After development, they were fixed for about 20 minutes, washed in running water for a t least one hour, rinsed in distilled water, and dried in air. The Gaertner visual microdensitometer, having a scale range of 0 to 100 divisions corresponding to density units of 0 to 4, was used to evaluate line densities.
After a sample of solder filings has been prepared and dissolved in hydrochloric acid in the usual way, and any tin in the stannic form has been entirely reduced to the stannous form, immediately place a small piece of solid carbon dioxide in the solution and place the flask in a cooling bath of ice and water. Add more small pieces of dry ice and maintain a vigorous evolution of gaseous carbon dioxide within the Erlenmeyer flask until the solution has been cooled t o room temperature and is ready for titration. Just preceding the titration, wash down the wall of the Erlenmeyer flask with distilled water containing a small piece of dry ice, add 5 ml. of starch solution as indicator, and titrate the solution with 0.10 N iodine solution. The use of solid carbon dioxide prevents the formation of stannic ion due to atmospheric oxygen, makes it unnecessary to employ a bicarbonate of soda solution as a wash water, and eliminates the necessity of setting up apparatus for passing gaseous carbon dioxide or any ot,her gas through the solution during cooling. Dry ice may serve equally effectively in other determinations where protection of the solution from atmospheric oxidation is important.
Literature Cited (1) Scott, W. W. “Standard Methods of Chemical Analysis”, pp. 426-8, New York, D. Van Yostrand Co., 1917.
