Sulfur Determinations with a Modified Lindberg High Frequency Combustion Furnace ALBERT C. HOLLER AND ROSEMARY KLINKENBERG Chemistry Disision, Twin City Testing and Engineering Laboratory, S t . Paul V4,Minn.
HE combustion method for the determination of sulfur in Tferrous metals ( 1 , a, 10, 111, copper-base alloys (S,6,71, coal, and coke (6) is increasing in popularity because of its speed, aecumcy, and simplicity. This paper describes certain modifications which were made to B Lindherg high-frequency combustion furnace in order to obtain accurate sulfur values, and procedures for me with this furnace. The furnace makes use of high frequency currents t o heat the ferrous metals to the oombustiou temperature, thereby differing from the ordinary resiRtance furnace, and necessitating different teehniqies in order correctly to burn nonferrous alloys, r o d , and coke. APPARATUS AND REAGENTS
Apparatus. A Jlndherg high frequency combustion furnace, Model LI-500-A. M ~ D I P I C A T I TO ~ N FURNACE S (see Figure 1). The dispersion plug WBB removed and a plug (1 gram) of glass wool, placed near the top of the Vycor combustion tube, was used in its place. A dome cap of borosilicate glass wa8 subRt,ituted for the one made of aluminum alloy. The remainder of the apparatus was standard glassware as used in the ordinary combustion sulfur methods (B, 6),with the exception of the cupelets (combustion boat.s), whioh were ohtsined f r o m Scbaar and Co., Chicago, Ill. Reagents. RR Alund u m , %mesh, N o r t o n Co., Worcester, Mass. Tin metal. manulated,
over at the start of the combustion, and the remainder W I ~ , ~iur ignition of the sample is complete and fusion of the oxides takes place. After appronim~tely2 minutes titrate the sulfuric acid formed with standard sodium hydroxide to the blue end point, using bromoere~olgreen a8 the indicator. Continue the eombustion until no more sulfuric acid ia formed. Turn off the plate switch and fluah the system for 1 minute. Momentarily open the tube by slightly lowering the loading mechanism to wash out any sulfuric acid that may have formed in the delivery tube and titrate the absorbing solution to the end point. The number of milliliters of standard sodium hydroxide used times its factor (expressed in ternis of per cent sulfur per milliliter per 1 gram of
dum. Carry out the co%bustion and titration as for ferrous metals. Coal and Coke. Weigh out a 0.05- to 0.1-gram sample of the coal or coke, transfer to the bottom of the cupelet, and cover with a thin layer of Alundum. Cover the Alundum with about 1 P a m of Plast-Iron, and then with 1 gram of tin. Then cover the contents with nluudum, and follow the combustion and titration procedure as for ferrous metals. RESULTS
Ferrous Metals. Given in Table I are the results pbtaiued using the above procedure t o determine the sulfur content of a number of National Bureau of Standards standard samples of ferrous metals, which range from east irons to stainless steels. ‘Theaverage deviation was found to be 0.001%. Copper-Base Alloys. Table I1 gives the results obtained on two National Bureau of Standards standard copper-base alloys. Coal and Coke. As there were no standard coal or coke samples
D i v i s i o n , National Radiator Co., Johnstown, Pa. T h e b a l a n c e of the r e a g e n t s -s t a n d a r d sodium hydroxide, hydrogen peroxide absorbing solution, a n d bromocresol green indicatorwere prepared as directed by Woodward ( 1 1 ) and IIoller and Yeager (6).
Tahle 1. Results on Ferrous Metals Xational Bureau of Standards
Sulfllr
Solfar liuund.
7%
7%
0.071 0.101 0.079 0.272 o.087 0.426 0.031 0.005 0.018 0.017
0.071
+o.m
0.078
-0.001 +0.001
0.024
0.023
Present,
Skmple
4a. east iron iron .h sulfur rteel ( S I R XI 1 ;.€ rteeiI.
I.H. steel ic e1eotrir steel h riiioon steel Ni steel (SAE 3110)
PROCEDURE
Furnace Practice. The followine f u r n a c e practice w G used on all combustions r e g a r d l e s s of t h e m a t e r i a l . T h e Figure 1. Combustion FurE i h m k n t s w i t c h was nace turned on and the furnace dlowed to warm up for 1minute (9). The pedestal height was adjusted so that t.he initial burning took place a t ahout 250 ma. (read on grid milli2~nnmeter),gmdtdual1.y increasing to approximately 450 ma. toward the end of the combustion, and then decreasing again to about 175 to 225 ma. a t the end of the run. Ferrous Metals. Weigh out a 1-gram sample of the ferrous metal and transfer to a cupelet. Cover with about 1 gram of tin and sprinkle over the top Wmesh Alundum, so that the uuderlying tin and ferrous metal do not show through. Place the eupelet on the pedestal hearth and raise into the combustion tube. Lock into position by turning the handle into the slot provided, and adjust the oxygen flow to 1200 to 1500 ml. per minute. Turn on the plate switch to start the combustion and pass the products of combustion into the hydrogen peroxide ah,wrbing solution. A smitll amount of sulfur dioxide will come
Deviation.
7%
o.ow
-o.oo2
0.273 0.038 0.028 0.031 0.005 0.017
+a 001 +O 001 &o.ooo *o.ooo -o.ooi
-o.ooi
0.046
0.004
0.004
0.008
0.006 0.018
0.016: 0.033
*o.ooo -0.001 -o.oo?
f0.002 -0.001
0.032 0.023
0.024
-u.ooi
Tahle 11. Results on Copper-Rase Alloys National B m e ~ uof Standards Shinple 124b. onnee metal 63b. phosphor bronze
Solfar present, % 0.041 0.16
Sillfm.
Found, %
Deviation.
0.044
o ,003
%
0.17
0 02
Tahle 111. Results on Coal and Coke Sulfur Present, Tvoe ”. of C o d
Cole Biturninovs e0z1 nituminoua c o d Lignite Bitumlnoua a d nitunrinorls cod
1696
46 0.54 3.97 3.09 0.79 0.73 1.23
Sulfur Found. %
Deviation.
0.56
+0.02
3.92 3.07 0.78 0.65
1.23
m,
-o.o5 -0.02
-0.01 -0.08
zto.00
1697
V O L U M E 23, N O . 11, N O V E M B E R 1 9 5 1 available, samples were taken for analysis which has been previously analyzed for sulfur by the gravimetric barium sulfate method of the American Society for Testing Materials (4). The results are shown in Table 111. The average deviation was found to be 0.03%. DISCUSSION
Yery erratic sulfur values were found using the original Lindberg high frequency unit. These poor results were traced to the aluminum alloy dome cap and the metal spring of the dispersion plug, and were probably due to the attack of the metallic parts by the sulfur dioxide liberated during the combustion. On substitution of a borosilicate glass dome cap, accurate sulfur values were once more obtained. A plug of glass wool was found to be very efficient in removing the metallic oxides from the gas stream. If the amount of Alundum placed on top of the charge is too light, large amounts of metallic oxides will be volatilized, if it is too heavy, the molten oxides will spatter. The correct amount was found to be that which just covered the charge so that the underlying metals did not show through. The sulfur values for the coal and coke samples are in good
agreement IThen the errors ( 8 ) i n thc determination of sulfur as barium sulfate are considered. LITERATURE CITED
Aites, \V. K., Steel, 125, 92 (Dec. 12, 1949). Am. Soc. Testing Materials, “A.S.T.M. Methods for Chemical Analysis of Metals,” pp. 20, 129 (1950). Ibid., p. 286. Am. SOC. Testing Materials, “A.S.T.M. Standards 1949,’’ P a r t 6 , p. 595. Bondarenko, M. M., Krolouets, S. hl., and Belyaeva, A. P., Zavodskaya Lab., 14, 991 (1948). Holler, A. C . , and Yeager, J. P., F o u d r u , 72, 83 (1944). Holler, A. C., and Yeager, J. P., 1x0. ENG.CHEM.,ANAL.b;i>.. 16,349 (1944). Kolthoff, I. M., and Sandell. E. R . , “Textbook of Quantitative Inorganic Analysis,” p. 329, Ken l o r k , Macmillan Co.. 1947. Lindberg Engineering Co., Chicago, “Instructions for Installation and Operation of Lindbei g High Frequency Combustion Furnace, LI-500-,4,” 1950. Lundell, 0. E. F., Hoffman, J. I., and Bright, H. A , , “Chemical Analysis of Iron and Steel,” p. 249, New York, John Wiley &- Sons, 1931. U. S. Steel Corp., “Sampling and Analysis of Carbon and Alloy Steels,” p. 309, New York, Reinhold Publishing Corp., 1938.
RECEIVED hlay 2, 1951.
Microdetermination of Saponification Equivalent CECIL H. VANETTEN, Northern Regional Research Laboratory, Peoria, 111. of the micromethods for determination of saponification M OST equivalent described in the literature consist of essentially a
reduction in the size of sample and apparatus of conventional macromethods for determination of saponification number of fats and oils (2-5, 7 ) . The ingenious method of Marcali and Rieman ( 6 ) , in which the blank is eliminated, is limited to materials in which the organic acid derived from the ester is soluble in benzene. Mitchell et al. ( 8 ) reported a semimicroprocedure using 1 to 2 me. of sample and its application to a variety of synthetic esters. The present paper describes a micro saponification technique which is different from the techniques described in the above references. I t is applicable to a wide range of esters, including volatile esters and some requiring drastic treatment in order to bring about complete reaction. APPARATUS AND SUPPLIES
Reaction Tubes. For solids and high-boiling liquids, thinwalled soft glass tubes, from 50 to 60 mm. long and from 5 to 8 mm. in diameter, were sealed a t one end. For volatile liquids, similar tubes (Figure 1) with a capillary in the center were used. The diameter of these tubes was not critical. For low-boiling esters, the capillary must be small enough to prevent loss of sample. Reagent-Dispensing Tube. A convenient dispenser for the alkali solution was an ordinary 10-ml. glass stopcock microburet, protected a t the top with an Ascarite tube. The tip of the buret was drawn out, so that the reagent could be easily delivered to the bottom of the reaction tube without touching the side walls. Support Rack. During saponification, the tubes were attached t o a metal rack by means of rubber bands. This rack consisted of a notched metal strip about 3 cm. wide and 20 em. long with numbered positions to accommodate eight tubes. With the use of this rack the tubes could not become interchanged, and a series of tubes could be agitated simultaneously by rotating the rack. REAGENTS
Potassium hydroxide solution, 1.0 to 1.3 N in technical grade ethylene glycol. Diethylene glycol (Q),water, and ethanol were equally satisfactory for those esters soluble in them, Standard hydrochloric acid, 0.01 A‘ aqueous. Mixed indicator. One part of 0.04% aqueous cresol red and 3 parts of 0.04y0 aqueous thymol blue. 1-Propanol. Ethanol, %yoor absolute. Sodium hydroxide, approximately 0.01 N .
PROCEDURE
For solids or high-boiling liquids, about 0.05 me. of the ester was weighed to the nearest 0.005 mg. in the reaction tube. In the case of viscous liquids the material was forced from a transfer capillary (inside diameter about 2 mm.) by using a small rubber Q I
\\
v
Figure 1. Reaction Tuhe for Volatile Esters tube as a pressure bulb. Potassium hydroxide solution (I00 to 175 mg.) was delivered on the sample from the tip of the reagentdispensing tube. The final weighing to determine the weight of potassium hydroxide solution was made to the nearest 0.1 mg. About 0.1 ml. (0.2 to 0.3 ml. with less soluble esters) of 1-propanol was delivered into the tube from a medicine dropper or micropipet, and the tube was centrifuged for about 30 seconds. The open end of the tube was sealed in a micro flame. I n the case of volatile liquids, the tube in Figure 1 was used. The sample was inserted by means of a capillary about 0.8 mm. in inside diameter into the weighed tube a t point b. After a suitable weight of sample had been delivered, the tube was centrifuged to force the sample through the capillary to position c, and its weight was accurately determined. Reagent was introduced a t point b and centrifuged into c, and the final weight was taken. 1-Propanol was introduced and centrifuged into c, and the open end of the tube was sealed a t a. The solution wae mixed from one end of the tube to the other through the capillary by centrifugation. The sealed reaction tubes, mounted on the support rack, were heated in an oven a t 100” to 105” C. for 1 hour. After 15 to 30 minutes in the oven, the eamples were thoroughly mixed by
