mark with chloroform and mixed very well. Measure the absorbance of this solution at either 380 or 425 mF against a blank containing all reagents with no aluminum.
RESULTS
KO high-temperature alloys \yere available as standards for aluminum. An indication of accuracy, at least in so far as color development and pho-
DISCUSSION
It is not advisable to make the p H adjustment before adding the sodium cyanide solution because the basic cyanide vi11 render the solution too alkaline. The formation of hydrogen cyanide is kept a t a minimum due to the addition of sodium sulfite solution. After the addition of the saturated sulfite solution, the medium is a t a p H of S, or slightly alkaline, in which case hydrogen cyanide will not be evolved.
Table II. Comparison of Per Cent Aluminum“ Found b y Gravimetric and Colorimetric Methods
Sample 3v4 3v5 3V8 3\19 2971
/
80-
2972
2702
2 60-
2973
g 50m
I- 40-
30E20-
Io-
I
I
I
I
I
I
I
I
tometry are concerned, is shown in Table I. Heats of a nickel-base alloy containing major amounts of chromium, cobalt, titanium, and iron were analyzed using the recommended procedure (Table 11). Figure 1 illustrates the nearly linear curves obtained a t 380 and 425 mp. Figure 2 shows the maximum wave length a t 380 mp.
Color-
Gravimetric* 2.95 2.93 3 04 3.01 3 05 3.00 3.06 3 05 1.51 1.50 1.26 1.25
imetric 2.90 2.91 3 00 3.00 3 00 3 00
1 .oo
1.oo
3.07 3 05
1.50 1.50 1.25 1.25
1.00 1 .oo 3190 4.50 4 55 4 53 4.54 3191 4 25 4.25 4.25 4 25 3192 4.00 4.00 4 00 4 00 Each sample was run 5 times with each procedure, having a deviation of no more than 0.05y0 of the total aluminum. * Modified method of Blum ( 1 ) . 0
LITERATURE CITED
(11 Blum, W.,cJ. A m Chern. SOC. 38, 1282 (1916). (2) Chenery, E. >I., d n a l y s t 73, 420 (1950). (3) Gentry, C. H. R., Sherrington, L. G., I b f d . , 71, 432 (1946). (4) Kassner, J. L., Ozier, XI. A., ANAL. CHEM.23, 1453 (1951). (5) Lundell, G. E. F., Knowles, H. B., Bur. Standards J. Research 3, 91 (1929). Banks, (6) IIargerum, D. IT., Sprain, W., C F., ANAL.CHEM.25,249 (1953). ( 7 ) Short, H. G., Analyst 75, 420 (1950). (8) Smith, G. F., May, R. L., J . A m . Ceram. SOC.22, 31 (1939). (9) Smith, W.H., Sager, E. E., Sievers, I. J., ANAL.CHEM.21, 1334 (1949). (10) Sudo, Emiko, Sci. Repts. Research Insts , Tohoku Unzo., Ser. A, 4 , 268 (1952). (11) Thrun, TT’. E., A \ ~ L . & E x . 20, 1117 (1948). (12) White, C. E., Lowe, C. S., IND. ESG.CHEY.,AUAL.ED. 9, 430 (1937). (13) Kiberlev, S. E., Bassett, L. G., ANAL. CHEV.21,609 (1949 I.
RECEIVED for review Xovember 7 , 1957. Accepted October 10, 1958.
Determination of Oxygen in Copper WILLIAM F. HARRIS and WILLIAM M. HICKAM Research laboratories, Westinghouse Electric Corp., Pittsburgh 35, Pa.
b A rapid method for determining oxygen in copper is necessary for effective refinery control. When copper i s melted in a graphite boat under vacuum conditions, essentially the only gas present in the system is carbon monoxide. The gas pressure can b e measured with a mercury manometer. The results obtained by this method are comparable to those obtained by the conventional vacuum fusion technique and are not subject to sulfur errors. A determination can b e accomplished in 15 minutes, so that it is possible to make any necessary adjustments in the oxygen content of the copper heat immediately.
B
of the adverse effect that oxygen can have on the physical properties of copper, a control of the oxygen content during refining is deECAUSE
sirable. Metallographic inspection, vacuum fusion, and hydrogen reduction methods have been used for laboratory control; however, the usefulness of these methods for actual refinery operations has been limited b y the time lapse between sampling and results, sulfur interference, and the complex equipment required. For effective refinery control the time between sampling and results should be 20 minutes or less and the equipment should lend itself to operation by production personnel. A simple apparatus using the vacuum fusion principle has been developed from that suggested in earlier work ( I ) . This apparatus eliminates the chief disadvantages of the conventional vacuum fusion methods. As the time of analysis is only 15 minutes, it is possible to determine the oxygen content of a copper heat before and during pour-
ing, so that further deoxidation can be accomplished m-ith little delay. The method consists of melting the copper contained in a graphite boat in an evacuated system and measuring the pressure of carbon monoxide liberated. The apparatus now a t the Restinghouse Copper Mill is being used for the determination of oxygen concentrations from 0.01 to 0.5%. APPARATUS
The apparatus is essentially a standard volume equipped with a mercury manometer (Figure 1). The 9-inch quartz furnace tube is joined to the manometer section through a 40/50 standard-taper ground-glass joint sealed with Apiezon W high vacuum wax. The rest of the system is made from 8mm. borosilicate glass tubing. The 12/30 glass joint is used for attaching the apparatus to a mechanical vacuum VOL. 31, NO. 2, FEBRUARY 1959
281
.
Figure 1.
Figure 2.
pump for evacuation or to a mass spectrometer for 3 complete gas analysis. The graphite boat was fabricated from Xational Carbon spectroscopic grade graphite. The boat is 11/2 .X '/zX 3/8 inch and fitted with a graphite cover '/8 inch thick. It will hold copper samples up to about 10 grams in weight although the usual sample size is 2 or 3 grams. The volume of the furnace-manometer section was determined by adding 3 known pressure of gas, expanding the gas into a k n o m volume, and remeasuring the pressure. For this system the volume a t room temperature was 180 ml. Because the pressure of gas liberated during fusion is measured with the boat a t 1150" C., it is necessary to correct for the expansion of the gases in the system a t operating temperature. This correction was made by admitting a known pressure of carbon monoxide to the sj.stem a t room temperature after a thorough degassing of the boat, heating to the operating temperature for 10 minutes, and measuring the incrrase in pressure. The pressure increase mas about 25%, so all readings were corrected accordingly. PROCEDURE
At the beginning of each day the empty crucible is inserted in the quartz furnace tube and the furnace tube \Taxed to the manometer section. The system is evacuated with a Welch DuoSeal mechanical pump and the boat degassed for 20 minutes a t 1150" C. A 5-kw. Kestinghouse radio-frequency generator is used for the induction heating. K h e n the furnace has cooled sufficiently for convenient handling, the wax seal is broken, the sample placed in the boat, and the furnace reassembled. The system is pumped out for 5 minutes, the stopcock isolating the furnace-manometer system closed, and the induction heating started. The temperature is raised to about 1150" C. A 10-minute extraction of the gas is usually sufficient, although heating is continued until the manometer reading is constant. The same procedure is followed for the determination of the blank, which is consistently 1 mm. of mercury. For the next sample it is necessary only to remove the melt from the boat and add the next copper 282
ANALYTICAL CHEMISTRY
.
Time, M mutes
Fusion apparatus
Carbon monoxide pressure increase in furnace
samule. S o degassing between determinations is necessary. EXPERIMENTAL
To obtain satisfactory results with this apparatus it is essential to have primarily one gas present in the system when the pressure measurement is made. At the concentrations of oxygen under consideration, the solubility of hydrogen in copper is negligible. The nitrogen solubility is extremely small and can also be neglected. Sulfur, however, is known to interfere in the vaccum fusion determination of oxygen. Previous experience indicated that when copper n-hich contains sulfur is melted under vacuum conditions, some sulfur dioside is liberated. The amount of sulfur dioxide depends on both the sulfur and oxygen concentrations in the copper. Therrfore, in a conventional vacuum fusion system where a fast pumping speed is maintained to remove the gases from the furnace, the removal of sulfur dioxide will result in low oxygen results. The effect of the sulfur dioxide on the usual copper oxide-rare earth oxide catalyst is also not drsirable as the sulfur dioxide appcars to be absorbed and then slowly rcleased over a long period of time. I n the present apparatus the gases are not removed from the furnace so the system can be more simply described in terms of thermodynamic relationships than in continuously pumped equipment. If any sulfur dioxide is liberated during the extraction of the gases from the copper, it will be converted to carbon monoxide by the follon-ing equation:
so, + 2c
=
2co + s
From the equation Fo = -RT In K , the equilibrium constant, K , can be evaluated
I n operation, the graphite boat is a t 1150" C. but the end of the furnace tube near the 40/50 joint is about 70" C. Therefore, the sulfur produced by
reduction of the sulfur dioxide with carbon condenses a t the cooler end of the tube and the pressure of sulfur in the system is equal to the vapor pressure of sulfur at io" C. Because of this, the pressure of sulfur dioxide that (
