V O L U M E 2 4 , NO. 5, M A Y 1 9 5 2 centrated hydrochloric acid and carrier sulfate solution to produce about 100 mg. of barium sulfate precipitate; heat to boiling; add 25 ml. of barium chloride solution (50 grams per liter) slowly with constant stirring; allow precipitate to digest for a t least 1 hour and to stand overnight before filtering. Transfer precipitate to filtration apparatus (Tracerlab, Inc.), rn ashing R ith alcohol and acetone. AIount precipitate with filter paper on brass disk (Tracerlab) for radiometric determination. In the case of solutions containing pyridine, after adding potassium permanganate and heating gently to oxidize the xanthatesulfur, neutralize the pyridine and render the solution acid (pH 1.0) by addition of concentrated hydrochloric acid. Then make up to 400-ml. total volume with water, and follow the procedure outlined above. The accuracy of the procedure was checked by taking 121.7 mg. of sodium sulfate, adding water to 400-ml. total volume; adding 1ml. of concentrated hydrochloric acid; heating; and adding 25 ml. of barium chloride solution, etc., which for four determinations yielded barium sulfate precipitates weighing 199.8 f 0.3 mg. (theoretical yield 200 mg.).
889 LITERATURE CITED
(1)
Carr, J. S.,S.M. thesis, Massachusetts Institute of Technology, 1951.
(2) Gaudin, A. hI., “Principles of Mineral Dressing,” New York, (3)
McGraw-Hill Book Co.. 1939. Gaudin, A. M., and Bloecher, F. W., Jr., Trans.Am. Inst. Mining
(4)
Gaudin, A. &I., and Schuhmann, R., Jr., J. Phys. Chem., 40,
Engrs., 187, 499 (1950). 257 (1936).
Glendenin, L. E., Nucleonics, 2, 12 (1948). (6) Glendenin. L. E.. and Solomon, A. K., Phus. Rev., 74,700 (1948). (7) Henriques, F. C., Kistiakowsky, G. B., Margnetti, Charles, and Schneider, W. G., IWD.EXG.CHEX.,ANAL.ED., 18, 349 (5)
11946).
Vincent, K. C., Sc.D. thesis, Massachusetts Institute of Technology, 1943. (9) TVark, I. W., “Principles of Flotation,” Melbourne. Australasian Institute of Mining and Metallurgy (Inc.). 1938. (10) Weiss, N., Trans. Am. Inst. Min. Engra., 183, 145 (1949). (8)
RECEIVED for review N a y 13. 1951.
Accepted August 30,1951.
Precision Determination of Carbon in Metals By a High Frequency Combustion-Volumetric Methods LEONARD P. PEPKOWITZ AND PAUL CHEBINIAK Knolls Atomic Power Laboratory, General Electric Co., Schenectady, 11’. Y. SIMPLE consideration of the volumes and kinds of measurevolume a t constant pressure, temperature, and barometric pressure-made in the usual macrovolumetric determination of carbon dioxide indicates that carbon should be determined volumetrically with considerably better precision and accuracy than at the present time. A gas buret can be easily read to f 0.15 cc., which is equivalent to =t0.00270carbon on a 1-gram sample. The advent of the modern high frequency induction heating devices has provided a convenient method for attaining high enough temperatures so that this factor is not limiting.
A ments-Le.,
SOLID PLUG
PACKED WITH GLASS WOOL II cn,
I
Figure 1.
Saturator
The apparatus used in this investigation was a Lindberg H-F combustion unit and volumetric carbon determinator with some modifications which are described below. Using the equipment without modification and the procedure described by the manufacturer ( I ) , a mean error of &0.022% was obtained on four Kational Bureau of Standards standard steels. This value is somewhat better than the usual variation obtained withvolumetric methods, but does not approach the precision and accuracy inherent in the volumetric method.
The various steps in the procedure were examined critically and the following modifications and changes were made in the apparatus and manipulation, which resulted in obtaining a precision of =!=0.00370 with a lower limit of precise measurement of 0.02% carbon with a 1-gram sample. This is equivalent t o results obtained with a precise gravimetric method. The first observed source of error is the nonreproducibility of reading the thoroughly cleaned gas buret when using the prescribed leveling solution #(2070 sodium sulfate plus 5% sulfuric acid). Smooth drainage and reproducible values were obtained by dri-filming (Dri-film 9987, a General Electric Co. organosilicon product) the inside of the buret. This simple treatment not only corrected the drainage errors but immediately made apparent the most serious error in the original method. The dry oxygen from the combustion unit does not come to water vapor equilibrium with the leveling fluid because of the geometry of the gas buret and short time of contact before it is pushed over into the potassium hydroxide absorption pipet. In the absorption pipet, a water-vapor pressure equilibrium is established, as the gas has a large contact area with the potassium hydroxide. The net result is that the initial volume readings are low and erratic. In the cam of blank determinations, negative values are often obtained because of this increase in the pressure of the gas following the carbon dioxide absorption. Before drifilming, this effect was lessened somewhat because of the multitude of droplets adhering to the walls of the gas buret. This condition was rectified by the very simple expedient of passing the gas from the combustion unit through a saturator (Figure 1) filled with the leveling solution and placed just before the four-way stopcock of the gas buret. This modification immediately increased the precision of the method and made it comparable with gravimetric methods. A number of other small but important changes resulted in more precise values.
Glass tubing with Tygon connections was used t o connect the combustion unit directly with the oxygen flowmeter and the gas buret. -4stopcock was placed between the combustion unit and the gas buret to control the gas flow. This precaution eliminated the extra lengths of copper tubing and two needle valves which proved to be unreliable. For precise results, no dependenbe can be placed on the check valves to define the volume of the gas, since both the potassium
890
A N A L Y T I C A L CHEMISTRY
Table I.
Accuracy and Precision Obtained with Standard
Steels Carbon Carbon Present Found
Sanilile
% 8e Besseiiier steel
2 l c Bessemer steel
50b K-Cr-V steel 72d Cr-RIo steel 132 N o - W C r - l ’ steel 151 boron steel 153 Co-310-W steel
b
0 0 0 0 0 0 0
S o . of Detns.
70
“0
069 482 i28 310 803a .55b
864
067 479
0 0 0 0 0
Av. Dev. from Nean
3Iean Error
12 11
725 306 802 0 543 0 865
+O =tO x0 +O
2
? 6
2
.I\ .
5%
003 006 003 004
1 0 007 1 0 007 001
+o
r O 004
& O 002 + O 006 i.0 +o 002
t O 006 zzo 004
+O +O
003 003
Ox>-gen flow 1000 1111. per minute. S B S provisional ralue
hydioxide solution and the leveling solution will creep past the valves. This condition is most serious with the potassium hydroxide absorbing solution and was eliminated by never lowering the leveling bottle belon- the bottom of the buret. The potassium hydroxide was displaced upward to the check valve by blowing through a tube attached to the vent of the absorption pipet. The potassium hydroxide solution was brought to a constant level by this means in each determination before closing the fourway stopcock By not lowering the leveling bottle below the bottom of buret another source of error is eliminated. When the leveling bottle is lowered below the bench top the leveling solution is drawn out of the buret, which often results in trapping some of the gas in the tubing connecting the leveling bottle and the gas buret. This results in high values, because the trapped gas is read as cRrhon dioxide.
accuracy (mcan error) and the precision (average deviation from mean) of the procedure. The present method has been applied to other materials beside steels. Its applicability depends on ascertaining the proper bedding material for the purpose, which may be an accelerator or a deaccelerator, depending on the metal and its rate of oxidation in oxygen. For 0.5-gram samples of titanium, vanadium, and and zirconium the following bedding materials are recommended : titanium, 1.5 grams of cupric oxide; vanadium, 0.5 gram of 30mesh lead; zirconium 1.5 gram of a mixture of 6770 powdered ~ these metals is iron and 33‘; cupric oxide. The osl-gen f l o for 700 to 1000 nil. per minute. Following the acceptance of this paper for publication, the method as used by E. L. Simons of the General Electric Research Laboratory. He observed a slon- equilibration of the gas with the leveling solution following the absorption of the carbon dioxide when the gas buret is t.horoughly dri-filmed, SO that no drops of leveling solution adhered to the walls of the buret. This equilibration is required, because the vapor pressure of water is not identical above the potassium hydroxide solution and the leveling solution. This difficulty can be eliminated by dri-filming only to the extent that reproducible and smooth drainhge is obt,ained but a few droplets of leveling solution adhere to the upper part of the gas buret. Under these condit’ions t’he final equilibration is rapid. The data in this paper nere obtained with a gas buret dri-filmed in this fashion. LITERATURE CITED
(1) Lindberg Engineering Co., Chicago, Ill,, “Instructions for the
EXPERIXIEhTAL RESULTS
The data in Table I were obtained with the modifications described above. All other conditions were those specified by the manufacturer-i.e., 0.25 gram of 20-mesh tin as an accelerator and an oxygen flow of 700 ml. psr minute. The data indicate the
Lindberg Carbon Determinator.” RECEIVEDfor review June 11, 1951. -4ccepted October 31, 1951. The Knolls Atomic Power Laboratory is operated b y the General Electric Co. for the Atomic Energy Commission. The work reported here was carried o u t under contract S o W-31-109 Eng-52.
Test for Highly Active Methylene Groups PETER F. WARFIELD Ansco Research and Development Laboratories, Binghamton, .V. 1-
4 V E R Y convenient test for highly active methylene groups in organic compounds exists, but does not appear to be 11-idely known except by those working on the preparation of color formers for use in color photography. A variation of this teat appears in an article by Weissberger and Porter ( I I ) , but this variation involves the use of photographic film and is not so adaptable to laboratory usage. 9reaction involving the coupling of pnitrosodimethglaniline, which leads to the formation of the same dyes as are produced in the test described in this paper, is given in another article by Keissberger and Porter ( I O ) . The reactions involved in this test constitute the basis of the presentday processes of color Photography (6)and date back to the early work of Fischer and Siegrist ( 3 ) . The over-all reaction may be written:
SH,
‘Rz SRJ
\ -
il
-
C-X=a=XR,
/
A
B
~
I The photographic latent image is the oxidizing agent in the usual process for color photography, but for the purposes of this
test, such compounds as potassium ferricyanide and aninioniuni persulfate are more suitable. There is considerable discussion as to the mechanism of this dye-forming reaction (1, 4, 6-8, IS), but such discussion lies outside the scope of this paper. The Droduct of this reaction is a dye whose color may range from yellow to green, depending upon the nature of the activating groups attached to the active methylene radical. Substituents in the phenylenediamine molecule are also important in determining the final color, but we are here concerned only with different active methylene compounds. S o t all groups known to organic chemists as “active methylene groups” will enter into this reaction. I n fact, it is generally necessary that the methylene group have two of the more powerful electron-attracting groups (such as -CN, -COR, and -COtR) attached to it, but when the methylene group is part of a fiveor six-membered ring, one such activating group will often suffice. For example, acetophenone with only one activating group does not react to produce a dye, but dibenzoylmethane with two such groups gives a reddish yellow dye. However, phenol, which has only one activating group, can produce a color in this test, probably because of the resonance stabilization of the phenolate ion. The active resonance structure is given in IIC. The effect of substituents in the phenolic nucleus upon the color of the dye produced by reaction with a substituted p Phenylenediamine is discussed in three papers by Vittuni and Brown (9).
