A N A L Y T I C A L CHEMISTRY
1612 Table 111. Precipitation of O s m i u m by T h i o n a l i d e Sample S o .
Reduced Precipitate
Residue
Osmium Volatilized
Deviation
Mg.
Mg.
Mg.
72
5.232 5.170 -0.3 0.062 5.239 0.042 5.197 +0.3 5.245 5.173 -0.3 0.072 5.310 0.116 5.194 +0.2 AV. 5,257 0.073 5.184 0.3 The result obtained by hydrolytic precipitation was 5.245 mg. with a deviationof0.170. 1
2 3 4
constant weight. The filtrate was tested for osmium in the same manner as the filtrate from the hydrolytic precipitation. Twentyfive milliliters of 0.2 A’ hydrochloric acid were added t o the precipitate in the beaker and the beaker was placed on the steam bath for 15 t o 30 minutes. This process was repeated four times and t h e washings were tested for osmium. After the fourth n-ashing the precipitate was transferred to the crucible. The crucible was placed in the ignition tube and hydrogen allowed t o flow through the tube for 5 minutes before the burner was lighted. The precipitate wl-asdried with a low flame. As the temperature was increased the precipitate turned from brown t o black, and a yellow liquid appeared on t h e cool part of the tube. +4very disagreeable odor was also noted. The precipitate appeared as a small sphere assuming the gray color of osmium sponge. The precipitate was then ignited in hydrogen a t full heat for about 2 hours, cooled, and weighed as usual. KO osmium was detected escaping from the tube during ignition. a f t e r ignition t o constant weight, the osmium was ignited
strongly in air. The residue from this oxidation was ignited in hydrogen until its weight was constant.
A spectrogram of the residue revealed iron, silicon, and magnesium, but no osmium. Magnesium \vas used as a catalyst in the preparation of thionalide (14). The results are recorded in Table 111. Further investigations are being made to determine the optimum conditions for this precipitation and the applicability of the method to other organic precipitants. LITERATURE CITED
(1) Ayies, G. H., dx.4~.CHEY.,2 1 , 652-7 (1949). ( 2 ) Xyres, G. H., and Wells, TT’. K., Ibzd., 2 2 , 317-20 (1950). (3) Barefoot, R. R., hIcDonnel1, IT.J., and Beamish, F. E., I b i d . , 2 3 , 514-16 (1951). (4) Chugaev, L., Compt. rend., 1 6 7 , 2 3 5 (1918). (5) Gilchiist, R., B u r . Standards J . Research, 6 , 421-48 (1931). ( 6 ) Ibid., 9 , 2 7 9 (1932). (7) Hill, M. A., and Beamish, F. E., ANAL.CHmf., 2 2 , 590-4 (1950). (8) Lebeau, P., and Jolibois, P., Compt. rend., (17 146, 1028 (1908). (9) Rogers, W.J., Beamish, F. E., and Russell, D. S.,ISD. EXG. CHEU.,AKAL.ED., 1 2 , 5 6 1 - 3 (1940). (10) Sandell, E. B., Ibzd., 16,342-3 (1944). (11) Teeter, K. G., unpublished research report. (12) Thiers, R., and Beamish, F. E., ANAL.C H E l r . , 1 9 , 4 3 4 (1947). (13) Thiers, R., Graydon, I T , and Beamish, F. E., Ibzd., 2 0 , 831-7 (1948). (14) Welchei, F. J., “Organic Analytical Reagents,” Vol. IV, p. 165, New Tork, D. Van Nostrand Co., 1948. RECEIVED for review January 28, 1952.
Accepted August 22, 1952.
Titanic Chloride as an Intermediate in Coulometric Analyses P.AUL ARTHUR AND JOHN F. DONAHUE’ Department of Chemistry, Oklahoma Agricultural and Mechanical College, Stillwater, Okla.
THE feasibility of using the titanium couple as an intermediate in coulometric reductions was tested by using it in the analysis of a series of iron samples. The use of standard solutions of such reducing agents as titanous chloride, chromous chloride or sulfate, stannous chloride, and cuprous chloride in direct titrations of oxidizing agents has always been seriously limited by theinconvenience involved in handling, storing, and using these reagents. The difficulty of avoiding air oxidation and the consequent change in titer is so great that most chemists use indirect methods of analysis rather than employ such reagents. It has been pointed out by Szebelledy and Somogyi (3) and demonstrated by Swift and coworkers ( 2 ) and Cooke and Furman ( 1 ) that such reagents, if they have suitable properties, can be generated electrolytically, and the unknown determined by application of Faraday’s laws. Thus Swift was able t o analyze solutions containing chromates and vanadates by means of electrolytically generated cuprous copper, while Cooke and Furman determined chromates and ceric salts through the medium of electrolytically generated ferrous iron. To be suitable for use in the constant-current coulometric determination of a given oxidizing agent, an intermediate must have the follov,ing Characteristics: I t s oxidized form must be reducible a t the electrode with 100% current efficiency; and its reduced form must be capable of reducing the unknown stoichiometrically and with reasonable rapidity. It was t o increase the number of substances known t o have the first of these characteristics and to make available more powerful reducing couples t h a t this research was undertaken. APPARATUS AND REAGENTS
Electrolysis Cell. The electrolysis cell consisted of a 150-ml. 1
Present address, Okmulgee, Okla
beaker covered by a wooden block, 100 X 100 X 18 mm., with a circular cavity in the underside, 5 to 6 mm. deep and just big enough to fit around the top of the beaker. Through this cover holes were drilled as follows: a 25-mm. diameter hole in the center t o accommodate the anode compartment; a 7-mm. hole t o admit the salt bridge of a saturated calomel electrode; and two 12-mm. holes fitted with rubber stoppers. Through one of these stoppers the glass tubing support for a platinum wire indicator electrode was inserted; through the other the heavy wire, x-hich supported and provided electrical connection t o the cathode, was passed. The anode compartment was a glass tube 25 mm. in outer diameter and 100 mm. long. I n the lower end there was a sintered-glass disk of medium porosity. Diffusion through this disk proving t o be too rapid, a suspension of finely powdered glass was d r a x n through it by suction until the pores were sufficiently clogged to permit only a very small seepage. The electrolysis anode n-as a platinum gauze electrode taken from a set of ordinary electrodeposition electrodes. The cathode first used was made by spot welding a No. 18 B. and S. platinum wire 100 mm. long to the back of a 50 X 50 mm. sheet of 0.005inch platinum. Later this electrode was converted to a gold electrode by heavily electroplating it with gold from a cyanide bath. The indicator electrode was a No. 22 B. and S. platinum wire, 3 em. long, sealed through the bottom of a soft-glass tube. About 2.5 em. of the wire extended outside the glass, and this part of the wire was bent upward and coiled around the glass t o form the electrode surface, Electrical contact t o the external lead was made in the usual manner by means of a globule of mercury. The saturated calomel reference electrode was the conventional type with a Bide-arm salt bridge fitted with a stopcock and a capillary tip, the latter passing through a 7-mm. hole in the beaker cover and dipping into the solution. The solution was stirred by means of a magnetic stirrer. Electrical Circuit. Eight 6-volt storage batteries connected in series were used as the power supply. Two 50-watt, 5OO-ohm variable resistors and one 50-watt, 10-ohm variable resistor, all connected in series, n-ere made into a resistance box which served
V O L U M E 2 4 , N O . 10, O C T O B E R 1 9 5 2 to caontrol the current through the cell. A Weston Model S o . 430 multirange milliammeter was used to measure the current, t'he instrument being calibrated frequently by potentiometrically measuring the ZR drop across a standard 1-ohm resistance r h i c h was connected into the electrolysis circuit. The circuit was arranged so that by throwing a double-pole toggle switch the electrolysis and a Gra Lab Universal timer could be started or st,opped simultaneously. Provision vias also made whereby a 25-ohm variable resistor, adjusted to pass approximately t'he same current as was being used for the electrolysis, could be thrown into the circuit in place of the cell. By allowing the current to flow through the resistor for 30 minutes before an electrolysis, it was possible to reduce the batteries to a stable working condition before runs were made. A Cenco potentiometer (Cat. S o 83411) was used for potentiometric measurements. In a number of cases the constancy of the current during runs was established by means of a Brown recording potentiometer (Model S o . l53x12T7-X-30)connected across a calibrated 0.1-ohm resistance placed in the electrolysis circuit. In no case was the measured variation in current greater than 0.1% even when no effort was made to compensate by manual adjustment of the resistances. Reagents. Ferric sulfate was made by dissolving 11.168 grams of standardizing-grade iron wire in hydrochloric acid, boiling the solution to half its volume with a large excess of nit'ric acid to oxidize the iron, then fuming off with 60 ml. of concentrated sulfuric acid. The resulting solution was cooled, diluted with water, cooled again, and made up to exactly 1 Mer total volume. This gave a solution 0.1 JI with ferric sulfate and approximately 1.5 -1-n-ith sulfuric acid. In measuring this iron solution into the electrolysis cell a 10-ml. and a 5-ml. pipet were used. Analyses were run on samples of the iron solution delivered by these pipets, the iron being determined by precipitating it as the hydroxide, igniting t'o the oxide and xeighing. Several such determinations gave an average delivery of 0,1100 =k 0,00010 gram of iron for the 10-ml. pipet and 0.05585 Z!Z 0,00005 gram for the 5-ml. pipet. I n the preparation of titanic chloride solution, hydrolysis caused great difficulty. +4ttemptsto dissolve the titanium tetrachloride in 0.1 S and 1 S hydrochloric acid resulted in unstable solutions; in 2 LY and 3 LV hydrochloric acid the solutions were stable, but the acidity was so great that hydrogen evolution invariably occurred at the cathode. The only way a solut'ion that \vas satisfactory in all respects could be obtained was by adding water slowly and viith stirring to 200 nd. of C.P. titanic chloride until violent hydrolysis ceased. The volume of the solution was then brought up t o 500 ml. by addition of more water. On analysis this solution was found to be 3.6 111 v-ith titanium, while titration with 0.1 N sodium hydroxide to the phenolphthalein end point gave an acid value corresponding t o 7.4 S hydrochloric acid. PROCEDURE AND RESULTS
In making a typical run, the switch to the warm-up resistance was closed and the current adjusted to the magnitude to be used in the electrolysis. During the 30-minute warm-up period required to stabilize the batteries, the milliammeter was calibrated, the potentiometer checked, and the solution to be used was prepared. This solution, which consisted of 10 ml. of the titanic chloride solution, 90 ml. of distilled water, and an exactly measured quantity of the ferric sulfate solution, was placed in the beaker (the cathode compartment) of the cell, and the anode compartment was filled to a level about 3 mm. above that of the other solution, with 1 S sulfuric acid. The electrodes were placed in position and adjusted so only the supporting wire of either was above the solution level. Carbon dioxide was bubbled through the solution for 5 minutes, and then the inlet tube was adjusted to cause the gas to flow over the solution for the remainder of the run. \\-hen this and the warm-up were completed, the magnetic stirrer was set to stir rapidly, v,-ithout cavitation, the warm-up resistance was cut out of the circuit, and the electrolysis and timer circuits were closed. During each run the current was watched, and adjustments were made manually whenever i t
1613
changed. Results obtained with the Brown recording potentiometer mentioned earlier indicated that such adjustments were probably unnecessary; for on the whole what small fluctuations occurred seemed to be self-compensating in the times required. The potential between the indicator electrode and the calomel electrode was measured periodically; these measurements were made with greater frequency as changes in the potential indicated that the end point was approaching. Initially in this research the end point was determined graphically. Efforts to obtain the end point automatically v i t h the Brown recording potentiometer failed. I t was found that there was a definitp time lag in the response of the indicator electrode, and undoubtedly some of the difficulty was due to a small delay in getting the reduction products thoroughly mixed through the solution. Consequently, the manual potentiometer v, as used, readings being taken with the electrolysis interrupted and after such readings became constant. A4fter several such runs had been made, however, it was determined from the curves that any potential from 0.2 to 0.3 volt should serve as the end point. The results shown in Table I were obtained by running the electrolysis as before until a rapid change of voltage indicated that the end point was very near. The electrolysis was stopped until equilibrium had occurred a t the electrodes; then it was continued to the chosen end voltage. Immediately after each run the cell \?-as emptied, and it and the electrode were rinsed with distilled water. The gold electrode \\-as kept immersed in lvater n-henever it was not in use.
T a b l e I.
Analysis of Iron S a m p l e s
End No. CurPoint ~ ~ of ~ rent^,~ Volt~ ment Runs Amp. age
I
S
0.1
0.3
Iron Found A i ~- -4verage ~ Deviation ~ gram Gram %0.1103
0.0005
0.45
:$ :?:;~
~ gram
-0.0012
0.23 -0,00032 0.2 0.05603 0.00013 I1 0.1 0.35 +0.00040 0,05575 0,00020 I11 0.05 0.2 a T h e values here give the order of magnitude only. I n each r u n the actual current used was measured, a n d this measured value was used in the calculations. I n practice the currents varied from the 0.1 ampere value not in excess of 2.5 ma., from the 0.05 ampere value by not more t h a n 0.1 ma.
Nature and Treatment of Cathode. Among the most important variables found in this work were those involved in the nature and treatment of the cathode. Platinum was found entirely unsatisfactory owing to the readiness with which hydrogen \vas evolved a t its surface, causing a great decrease in the current efficiency in so far as the intended reaction was concerned. Gold, with its much greater hydrogen overvoltage, was found quite satisfactory. HoTvever, it was necessary to condition the gold electrode, both when it was freshly prepared and again after each four or five runs, to prevent the evolution of hydrogen at a hat seemed to be active spots on its surface. This conditioning was done by polishing with moist sodium bicarbonate, rinsing, soaking for 10 minutes in concentrated nitric acid,rinsing again, then flaming. The flaming must be done with caution, however, as it is very easy to melt the gold. The flaming is best xhen done in the extreme tip of a well-adjusted Bunsen burner flame, care being taken never to let the gold get more than dull red-hot. The purpose of this flaming is to round off sharp points and the edges of fine scratches, for hydrogen evolution seems to occur more readily a t such places and, once it starts, the effect seems to spread. Variations in Titanic Chloride Solution. It has already been pointed out that only one successful n a y of preparing the stock solution of titanic chloride was found. If the order of mixingLe., adding water to the titanic chloride-is reversed, hydrolysis invariably occurs; if excess hydrochloric acid is used to prevent hydrolysis, hydrogen is evolved, even a t the gold cathode. Various modifications in the electrolysis mixtures were tried in order to determine critical concentrations needed. Efforts to reduce the acidity by addition of alkali invariably resulted in hydrolysis occurring, and an increase in acidity caused hydrogen evolution. Mixtures up to 30 ml. of titanic chloride stock solution to 100 ml. of final solution (approximately 1 Jf with titanic chloride) gave good results but presented no advantages over the
~
~
ANALYTICAL CHEMISTRY
1614 lower concentration recommended. Less than the 10 nil. recommended earlier resulted in hydrogen evolution, the latter increasing rapidly as the dilution was increased. It appears, therefore, that solutions 0.3 -1.I to 0.4 M with the titanic chloride are best, for such solutions give good results nithout unnecessary wasting of material.
and 0.18% for experiment 111. Although the average deviations (see Table I ) are somewhat higher for each, these results indicate that the titanium couple is suitable as an intermediate in coulometric reductions. In addition. its reduction potential is favorable for the reduction of many substances not readily reduced by any of the coulometric intermediates hitherto reported.
DISCUSSION
iilthough the primary purpose of this research mas to test the titanium couple as an intermediate rather than to devise a new method of analyzing iron samples, the results of these iion analyses provide evidence for the probable usefulness of this couple in coulometric reductions. Samples of iron of exactly the same size as those used in the runs listed in Table I, when analyzed by the well-established ferric oxide gravimetric method, gave average results for iron as follom: for experiment I, 0.1100 i0 0001 gram; for experiments I1 and I11 0.05585 zt 0.00009 gram. Comparing the averages found coulometrically with those determined gravimetrically and assuming the latter value to be correct, the actual error would be 0 27% for experiment I, 0.32% for experiment 11,
ACKNON LEDGRlEhT
The authors yish to express their gratitude to the Dow Cheniical Co., Midland, lIich., for its kindness in supplying titanium tetrachloride to complete this research r h e n other sources \%-ere unable to make delivery of this reagent. LITERATURE CITED
(1) Cooke, TT. D., and Furmnn. S . H.. ANAL.CHEX, 22, 896 (1950J. (2) Meier, D. J., Meyer, R. J., and Swift, E. H., J. Am. Chem. Soc., 71, 2340 (1949). (3) Szebelledy, L., and Somogyi. Z., Z. anal. Chem., 112, 313 (193s). RECEIVED for review February 4 , 1952. .4ccepted June 16, 1952.
Recording System for Mass Spectrometers K. K. JENSEN, W. E. BELL, AND F. E. BLACET D e p a r t m e n t of C h e m i s t r y , I-niversity of California, Los Angeles, Calif. SING a vibrating reed electrometer, a system for recording mass spectra has been installed on a Westinghouse Type LV mass spectrometer. This system is relatively economical in cost, simple in operation, accurate and dependable, and produces rapidly a directly readable chart on a pen recorder. The installation consists of a control box containing a Helipot and a magnet current meter, a vibrating reed electrometer and amplifier, a recorder, and a calibrating potentiometer. OPERATION
The main magnet current is varied from 100 to 7 ma. by means of an electronic circuit, controlled by a 15-turn Helipot which is driven by a synchronous motor through a gear reduction assembly. Scanning speed can be varied by changing the gear ratio. A Record switch controls both the Helipot motor and the chart drive motor in the recorder. The scanning motor drive is equipped with a magnetic clutch, which permits manual operation of the Helipot without strain on the motor gear-train. An interlock switch on the lid of the control box cuts off this scanning motor without disturbing the chart drive; hence, the scan can be interrupted a t any moment by simply raising the lid. This permits the magnet current to he manually set to any desired value and on closing the lid the scan starts from t h a t setting. A switch selects the direction of scan. The vibrating reed electrometer (manufactured by Ap lied Physics Corp., Pasadena, Calif.) consists of an electrometer t e a d which is mounted adjacent t o the ion collector plate, and an amplifier which is located on the control table. A decade range switch on the amplifier selects full scale sensitivities of 1, 10, 100, or 1000 mv. for recording mass peaks. Scale changes ap ropriate for each peak as the spectrum is being scanned are m a l e by the operator. With unfamiliar samples, a com lete scan is made on the 100-mv. scale; a second scan then can [e made over the desired mass range, and peaks easily recorded a t the proper sensitivity. The recorder is a 1-second response, 27.5-mv, strip-chart Brown Electronik potentiometer (manufactured by blinneapolis-Honeywell Regulator Co., Philadelphia, Pa.) with an auxiliary marker pen externally actuated by means of a toggle switch. An 11-inch chart having a 0.5-inch margin a t each edge for pertinent notes identifying mass peaks, magnet current, etc., is used. In order to record the full peak intensities, it was found that 23 minutes are required for scanning the mass range from 100 through 12. A section of the n-butane mass spectrum is shown in Figure 1. The signal to noise ratio is such that a peak intensity of 0.1 mv., corresponding to an ion current of 5 X 10-16 ampere, can easily be
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ol
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Figure 1.
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, -
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SCAN
151
I
; 1
Section of Normal Butane Spectrum
Recorded a t ionizing potential of 70 volts and with ion accelerating voltage set at 750
