V O L U M E 27, NO, 3, M A R C H 1 9 . 5 5 titrated with Fischer reagent to the end-point color of a matching
portion of the neck of the &sk does not become wet with gl$col. The mixture is then titrated with Fischer reagent until the loa er phase is near the end point color. The flask is again stoppered and shaken as before. The phases are allowed to separate and the titration is then completed with small increments of titrant until the color of the lower phase, as observed in the side well, matches the original color standard. When dense or viscous oils fraction before are analyzed, the addition of a light the pretitration of the glycol phase assists in the separation of phases. The application of this procedure for the determination of solubility of water in hydrocarbons is shown in Table 111. Replicate determinations indicated excellent precision of the method, except for the experiments a t 75' C., where difficulties in sampling caused somewhat poorer precision. The reverse dead-stop endpoint procedure also can be employed, using the dead-stop titration vessel (Figure 3, left). As long as the electrodes are immersed in the lower (glycol) phase, the end point can be readily determined when the flask is gently swirled. CONCLUSIONS
The usefulness of the reagent, solvents, and apparatus described has been demonstrated in the laboratories of the authors and others who have adopted several of these techniques but have
453 not included complete details in their publications (1, L ) . It
ACKR-OWLEDGMENT
The authors are indebted to W. B. M i l k a n for the design of the all-glass, siphon-type buret assembly and to R. H. Smith for Some of the experimental mrork involved, The Use of glycolWas suggested by H. R. Mcpyridine mixture as Combie, of Shell Chemical CO., Pittsburg, Calif. LITERATURE CITED (1) Brochmann-Hanssen, E., and Pong, P., J. Am. Pharm. d s s o c . , Sci. E d . , 41, 177 (1952). (2) Carter, R. J., and Williamson, L., Analyst, 70, 369 (1945). (3) Cornish, G. R., Plastics (London), 10, 99 (1946). (4) Davis, F. E., Kenyon, K., and Kirk, J., Science, 118, 276 (1953). (5) Fischer, K., Angew. Cheni., 48, 394 (1935). (6) Frediani, H. A., AXAL.C H m f . , 24, 1126 (1952). (7) Mitchell, J., Jr., and Smith, D. Rl., "Aquametry," p. 42, Interscience, Xew York, 1948. ( 8 ) Ibid.? p. 65. (9) I b i d . , p. 86. (10) I b i d . , pp. 146-54. (11) I b i d . , pp. 122, 162-8. (12) Jt7ernimont, G., and Hopkinson, F. J., ISD. ENG.CHEM.,ANAL. ED., 15, 272 (1943).
RECEIVED July
16, 1954.
dccepted October 22, 1954.
Apparatus for the Pyrohydrolytic Determination of Fluoride and Other Halides C. D. SUSANO, J. C. WHITE, and 1. E. LEE, JR. Analytical Chemistry Division, O a k Ridge N a t i o n a l Laboratory, O a k Ridge, Tenn.
A n apparatus for the pyrohydrolytic determination of fluoride and other halides is constructed entirely of nickel and stainless steel rather than platinum and quartz. The apparatus is economical, compact, and easily manipulated. .4pproximately 5000 determinations were made in 22 months before replacement of the reactor tube was necessary. The tube had been maintained at 1000" C. for approximately 3500 hours with daily cooling and reheating.
T
HE method of pyrohydrolysis for the determination
of fluorides was first exploited by Warf and coworkers ( I ) , who developed a method for the determination of fluoride in which steam is passed over a heated sample in a platinum apparatus. The volatile products of the pyrohydrolysis are then condensed and titrated: MF2 H20 -+ 110 2HF This reaction, in the case of many fluorides, is slow and is usually conducted at temperatures of the order of 1000" C. This high temperature and the known corrosive action of solutions of hydrochloric, hydrofluoric, and hydrobromic acids on metals dictates the use of extremely resistant structural materials. Rarf and coworkers (1) used platinum and quartz in the fabrication of their apparatus. This report concerns the use of nickel for this purpose. I t was desired that the apparatus be constructed of material of similar durability to platinum and require less initial expenditure. Xickel n-as chosen a8 the metal most likely to meet these requirements. In order to reduce the cost of the apparatus still further, stainless steel was to be used wherever possible. In the
+
+
design of the apparatus, prime consideration was given to these four factors: cost, durability, ease of manipulation, and compactness. DESCRIPTIO3 OF APPAR4TUS
The apparatus, in its final design, is shown in Figure 1. Ita over-all dimensions are 28 inches high, 21 inches deep, and 15 inches wide. Thus, it is possible to place two sets of apparatus in a 6-foot fume hood and still have ample space for titration and any other necessary operation. Steam is generated in a 1-liter flask, which is heated by an electric hot plate. The steam is passed through a line made of 1-inch (inside diameter) 316 stainless steel, which is heated by a 4 2 0 - ~ a t t5-inch , furnace operated a t 1000" C. A ball joint is used to connect the steam line to the reaction tube, which is made of nickel. The ball joint was fabricated by the machine shop and was patterned after the familiar glass ball joints. Fabrication was from nickel metal. Pertinent dimensions for the apparatus shown are: male joint, lQ/ls-inch outside diameter in TT idth; female, lj/lG-inch outside diameter broadening to 15/&ch outside diameter. The seal is made tight by the weight of the reactor tube. The reaction tube is heated by a 9-inch, 580-watt furnace. The condenser jacket is made of 316 stainless steel, as is the handle. The joint is made leakproof by means of the position and aeight of the handle M hich is 7.25 inches in over-all length, 4 inches of which is a I-inch bar and 3.25 inches of 0.25-inch 316 stainless steel rod. The handle Ti-eighs approximately 1.4 pounds. A photograph of the ball joints and ball joint loclr is sholvn in Figure 2. The apparatus is positioned so that the handle of the door lock is directlv in front of the operator. Thus, the receiver vessel for the condensate is located directly to the rear. This position is the most advantageous, a s it makes for simplicity in ihtroducing the sample into the tube and permits a full vien- of the ball joint and thus virtually eliminates any inadvertent loss of samples due to escape of hydrolysis products through an improper fitting of the loclr. The apparatus was designed t o use steam either generated by a water boiler or obtained from the plant steam line A condensing
ANALYTICAL CHEMISTRY
454 trap may be viewed st the bottom of the preheater. A water boiler was found to be the more reliable S O U I C ~of steam, &s steam taken from steam lines wm often contaminated with titratable acidic constituents. DISCUSSION
This apparatus has proved entirely satisfactory all respects over a period exceeding 2 years of almost constant use. With
Figure 2.
Close-up of sample en,trar port and ball joint lock
A new tube is conditioned by passing preheated ste
Figure 1. Front view of ,pararus Ior me pyrohydmlysis of halide showing nickel reaotor tube and r l l joints t n dnrmhilitu t ha. n ~.d n.^ r. n 1 hsvond ~io(in~ e 1 w_t _ a" - _ __.I -..."i, i." rl .I la. _li -..-n -..~ _m _r
rmnort "_ ___p"""
tians. Approximrutely 5000 determinations were made over a period of 22 months before replacement of the reaction tube was necessary. It was estimated that the tube had been maintained a t 1000" C. for approximately 3500 hours with daily cooling and reheating. No rupture of the tube was noted despite this treatment. When the tube was removed from the furnace and cooled in air, spalling occurred, probably due to the high cooling rate. A nickel insert urns welded t o the tube and the apparatus has been used for 8 mo ' '
constituents that may he titratable with base. Nearly 1500 determinations have been performed during this period. The replacement of the nickel reaction tube in direct contact with the furnace has been the only maintenance required in this period, which attests to the durability and economy of the apparatus. Monel metal has also been suggested a8 a possible material for this apparatus, but has not been tested in this laboratory. Stainless steel is not satisfactory because of its nonresistivity t o steam. The original model of the nickel apparatus was built with a stainless steel condenser line. Subsequent testing of the apparatus revealed that this was not satisfactory because significant amounts of iron are dissolved by the acid condensate which interferes with the titration of the acid with standard alkali solution. LITERATURE CITED
(1) Warf,
J. C.. Cline. W. D..
m d Tevebaugh, R. D.. ANAL.CHEM..
26, 342 (1954).
R E C E ~ V Efor D reviera July 24. 1954. Accepted Ootober 13, 1954. Work carried out under Contract No. W-7405-eng-26 st Oak Ridge National Lsboratory, oDerated by Carbide & Carbon Chemiaal Co., B division of Union
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