ANALYTICAL CHEMISTRY
804 Table 11.
1' " "
Effect of Chromic Acid Concentration on .4ccuracy
(Each solution contains 2.50 grains of fluoride per liter.) Av. Chromic Fluoride Acid Concn., Found, Error, F Grams/Liter Grams/Liter /O 200 2.49 -G.4 280 2.50 0.0 300 2.50 0.0 3 50 2 50 0.0 400 2 48 -0 8 I
I
80
100
and a constant quantity of fluoride. There was a slight error in the amount of fluoride found in the solutions a t the extremes of the cliromic acid concentration range. Standards Ivere prepared which contained constant amounts of chromic acid and fluoride ion per liter, and 2.5 grams of contaminating metals per liter. The addition of these metals had little effect on the accuracy of the method, as shown in Table 111. Insufficient washing of the heavy hydroxide and silver rhromate precipitates might explain the slightly lower result obtained on the one standard containing all the contaminants.
Tahle 111. Effect of 3Ietallic Contaminants on Accuracy l l p t e l l i c Contanrinants, Grams/Liter' Cr-+-, Fe++-, c r - - -, i ' r - -, S i *, Cu + -, S i I, Cu +, 2.5 2.3 2,5 2.5 2 . 5 of each
_____._ ~
~~
200
IS0 GrOI
IN
280
300
350
400
450
500
SAMPLE, G R A M S I L I T E R
Figure 1. Amount of reagents required for 4-ml. samples of varying chromic acid contents PI ecipitate the interfering metals as hydroxides because chromium constitutes such a large portion of the interfering ions. CONCLUSION s The results indicate that this method for determining fluoride provides more than sufficient accuracy for control of chromium plating baths. The method is being used very successfully to rontrol industrial chromium plating baths. .4fter the analyst has become familiar with the method, the det,erminat,ion can be completed in approximately 20 minutes. The usual quantities of contaniinating metals do not interfere.
+
Fluoride added, grams/liter 2 50 Fluoride found, 2.46 grams/liter 2.50 BY.error, % -0.8 1 Each bath contained 250
2 50 2 .jO 2.50 2.50 2.50 2.50 2,50 2.50 2.49 0.0 0.0 -0.2 &/liter chromic acid.
2.50 2.44 2.49 -1.4
-1graph was prepared showing the volumes of 1 . 0 s sodium hydroxide and 0 . 5 5 silver nitrate which are required to remove interfering metals from samples of varying chromic acid content (Figure 1). An excess of 2 ml. of sodium hydroxide and 5 ml. of silver nitrate over the stoichiometric amount required by the chromic acid content was added. This excess is sufficient t o
LITERATURE CITED
(1) .Ilrmstrong, W.D., J . Am. Chern. SOC.55, 1741 (1933). (2) Berzelius, J. J., Schweigg J . 16, 426 (1816); Rose, H., Ann. 72,
343 (1849).
(3) Hillebrand, W. F., Lundell, G. E. F., Bright, YI. S.,Hoffman, J. I., "Applied Inorganic .Ilnalysis," 2nd ed., 742, Wiley, Yew York, 1953. (4) Hoskins, 15'. M., Ferris, C. A., TND. ENG.CHEW,ANAL.ED. 8,
6 (1936). ( 5 ) Passel, F. (to United Chromium, Inc.), U.
S. Patent 2,640,021 (May 26, 1953). (6) Starech, J. E. (to Dnited Chromium, Inc.), Ibid., 2,640,022 (May 26. 1953). ( 7 ) Willard. H. H., Winter, 0. B., IXD. ESG. CHEM.,AKAL.ED.5, 7 (1933). RECEIVED for
review .iugust 20, 1955.
Accepted February 23, 1956.
Equipment for High Pressure Optical and Spectroscopic Studies ERWIN FISHMAN and H. G . DRICKAMER University o f Illinois, Urbana,
//I.
Equipment has been developed for making optical and spectroscopic studies in liquids at pressures up to 12,000 atm. A combination intensifier and bomb for spectroscopic measurements is described, as well as a source assembly particularly suited for use with a PerkinElmer single beam spectrometer. The use of synthetic sapphire windows permits measurements to be made in the wave-length range from 0.2 to 5.0 microns. Experiments are now being undertaken to develop windows which will permit extension of the wave-length range. With this equipment it is possible to study the effect of pressure in all phases of molecular spectroscopy. By suitable modification, it is possihle to measure the effects of pressure on the refractive index and on light scattering from polymer solutions, as well as related optical effects.
T
0 USDEKSTASD, correlate, and predict the physical
and chemical effects of pressure, its effect on intermolecular and intramolecular forces must be determined. Optical and spectroscopic investigations provide important evidence as t o the nature of these effects. This n-ork was confined to the study of equipment which was used successfully for optical and spectroscopic work in liquids at pressures up to 12,000 atm. When infrared spectroscopy is applied to liquids, the vibrational frequencies between atoms in a polyatomic molecule are observed. I n the pressure range mentioned, the effect most generally observed is that of crowding solvent molecules around a given bond. Because of the mutual polarizability of bonds, there is an attractive interaction which depends strongly on intermolecular distance. Solution properties, transport phenomena, and other macroscopic properties depend on these interactions,
805
V O L U M E 28, NO. 5, M A Y 1 9 5 6 and many pressure effects can be generalized from these measurements. I-ltraviolet spectra are primarily dependent on the electronic structure of molecules, v-hich can also be affected by interaction v i t h the solvent, and thus by pressure. I n particular, interesting pressure effects are anticipated in complexes such as the benzeneiodine system.
is satisfactory to calculatr the high pressure, making a 10% allowance for friction. The liquid to be studied is introduced directly on the high pressure side. This eliminates the necessity for separating the liquid from a pressure transmitting fluid, and considerably simplifies the operation. Thorough cleaning is, of course, necessary between runs, and coirosive liquids must be handled nith care WJIVDOW PLUGS 4nD UINDOWS
The principle of the window plug (Figure 2) is essentially the same as that established by Poulter ( 3 ) . The plug is made from inch in diameter a t Columbia Superdie tool steel. The hole is
Figure 2.
Figure 1.
Window plug
Spectroscopic bomb
1Iany other high pressure optical experiments, such as lightscattering studies of polymer molecules in solution, are also possible with the equipment desrribed. IYTEYSIFIER
Figure 1 s h o w a cross section of a reasonably small, portable high pressure apparatus 1vhic.h may be introduced into various epecatrometeis and other optical setups. The device consists of a n intensifier n-,th a 3-inch diameter low pressure piston and a l/?-inrh diameter high pressure piston, both utilizing conventional Bridgman unsupported a r m parking ( 1 ) . Any desired rtroke can be incorporated. but for most experiments 1 to 2 inches are ample. The t r o ends of the intensifier are conveniently made from SAE 4140, 4340, or 6150 steel hardened t o 48-50 Rockwell C. The over-all dimensions of the apparatus are 4l/2 to 5 inches in diameter and 10 to 15 inches high. The ram and high pressure piston are Superdie tool steel (Columbia Tool Steel Co., Chicago Heights, Ill.) hardened to 58-60 Rockn-ell C. The IOT pressure end can be attached to a portable pump and a free piston gage or a good Bourdon gage, such as a Heise gage. I n a special run before making optical measurements, the low pressure gage reading is calibrated against the reading of a manganin gage on the high pressure side, but for many purposes it
the surface of the windo\y and is tapered out a t the angle of the light beam. The main problem in the plug design is to make the surface hard enough to seat the window and still make the plug tough enough to Tvithstand cracks, particularly along the threads. The best compromise found in this laboratory is to make the face 55-56 Rockwell C and to draw the threads to about
806
ANALYTICAL CHEMISTRY
50 Rockwell C. Occasionally the face deforms a t this hardness, but plugs which have been used for 50 or more runs a t 10,000 to 12,000 atm. are still in service. The face of the plug is surface ground and lapped on 0000 emery paper. I t is convenient to screw the plug into a lapping block 11/2 to 2 inches in diameter, which prevents curvature of the surface. iThen the window seats on the plug and cannot be blown off orally from underneath, or when the plug can be picked up by lifting the window, without separating window and plug, the seal is satisfactory for even the least viscous liquids. The brass cap is useful for holding the window in place during assembling and dissembling, and while applying pressure. The plugs can be sealed in the bomb using steel unsupported area rings as described by Bridgman (1). The window spacing can be varied from less than 1 mm. to 1 em. or more by varying the ring thickness. Linde synthetic sapphires make convenient windows. The standard mindow used for this work was l / 2 inch in diameter and ' / 2 inch thick. It is important that the C axis of the crystal be perpendicular to the window faces. If a flatness of a t least 0.0001 inch is specified, the sapphires lyill usually seal as purchased; otherwise, they must be lapped myth diamond paste. The major limitation on the use of sapphire windoim is that they cut off radiation of wave lengths longer than 5 microns. Preliminary information ( 2 ) on sodium chloride window indicates that they are satisfactory a t least to 1000 atm., and calcium fluoride windows may be useful at still higher pressures.
>MISCELLANEOUS FEATURES
I t is frequently convenient to have a plug (particularly the bottom plug) tighten flush n-ith the surface of the bomb. A convenient device for this purpose is shown in Figure 3. The square head of the plug is replaced by a removable hexagonal nut which pins to the plug with three a/8-inch diameter pins of SAE 4340 steel hardened to 50 Rockwell C. The nut can be made easily removable and lasts indefinitely. A modified design of apparatus involving three nindow plugs, one perpendicular to the ot,her two, can be used for light-scattering and light-absorption studies. ACKNOWLEDGMENT
The authors wish to acknowledge the skillful machine work and useful suggestions of W. W.Demlow. LITERATURE CITED
(1) Bridgman, P. W.,"Physics of High Pressure," pp. 34, 37, 39, G. Bell and Sons, London, 1947. (2) Parsons, R. W., private communication, U. of Illinois, Urbana, Ill. (3) Poulter, T. C . , Phgs. Rev. 35, 297 (1930). RECEIVED for review October 13, 1955. Accepted February 4 , 1956. Division of Industrial and Engineering Chemistry, Symposium on Processing under Extreme Conditions, 128th Meeting, ACS, .Minneapolis, Minn., September 1955. Other papers presented a t this symposium appear in Industrial and Engineering Chemistru, May 1956. Work was supported in part by t h e Atomic Energy Commission.
Spectrophotometric Determination of Zirconium in T h o r i m LOUIS SILVERMAN and DOROTHY W. HAWLEY Atomics International, Division o f North American Aviation, Inc., Canoge Park, Calif.
A t a controlled high acidity, zirconium, in the amount of 0.005 to 0.350q& can be determined colorimetrically using Alizarin Red S. As much as 200 mg. of thorium can be tolerated in the presence of 10 to 700 y of zirconium. Acetone and heat accelerate the rate of color development and increase the stability of the color. Small amounts of iron and other metals normally present in thorium do not interfere.
A
N INVESTIGATION of new techniques for the purification
of thorium presented a need for a method for the determination of small amounts of zirconium in thorium. -4number of organic reagents have been studied and recommended for the direct colorimetric determination of zirconium. These include p-dimethylaminophenylazobenzenearsonic acid (6))alizarin ( 2 , 8), Alizarin Red S ( 3 , 4,9-11, fd), purpurin, ( 2 , 8) quinalizarin ( 2 , 8 ) , thoron ( 6 ) ,and chloranilic acid (10,13). I n their present form, these methods are time-consuming or require the removal of thorium if present in large amounts. Alizarin Red S (sodium salt of 3-alizarinsulfonic acid) showed the most promise, because the colors ordinarily produced by interfering metals (other than hafnium) are vitiated in strong mineral acid solution. The various contributory factors were studied to obtain the maximum absorbance due to the zirconium-Alizarin Red S lake under conditions that result in minimum interferences from other sources. REAGENTS
Standard Zirconium. Dissolve 35.33 grams of C.P. zirconyl chloride octahydrate (ZrOC12.8H20)in an aqueous hydrochloric acid solution (pH 1.2) and dilute to 1 liter with the same acid
solution. Standardize using the p-bromomandelic acid method (7). This solution contains 10 mg. of zirconium per milliliter. Prepare solutions containing 0.100 and 0.010 mg. of zirconium per milliliter by properly diluting the stock solution with the aqueous hydrochloric acid solution. Standard Thorium. Dissolve and fume 29.74 grams of thorium nitrate tetrahydrate [Th(r\;03)4.4HzO] with 150 ml. of concentrated perchloric acid. Dilute to 1 liter w t h water, making certain that the pH is approximately 1. This solution contains 25 mg. of thorium per milliliter. Analyze by precipitating the thorium as oxalate and weighing the oxide ( 2 2 ) . Colorimetric Reagent. Dissolve 500 mg. of Alizarin Red S (National Aniline Division, Allied Chemical and Dye Corp., S e w York) in a 2 to 3 hydrochloric acid solution and dilute to 1 liter with the same solution. Let stand for 2 days and filter through Whatman S o . 40 paper. The solution is stable for a t least 1 month. Sample-Diluting Solution. Prepare a hydrochloric acid-water solution having a pH of 0.70. PROCEDURE
Sample Preparation. Weigh a sample (metal or compound) containing 0.800 gram of thorium into a latinum dish. Add 10 ml. of concentrated nitric acid and a g w drops of 2% hydrofluoric acid. Warm to initiate the reaction, then remove from the heat. If the reaction becomes too vigorous, it may be moderated by the addition of water. When the reaction subsides and solution is complete, add 5 ml. of concentrated erchloric acid. Eva orate to near dryness and cool. Add 2 ml. ornitric acid and 5 m! of perchloric acid and again evaporate almost to dryness. Dissolve the residue in 5 ml. of 1 to 1hydrochloric acid with heat. Transfer to a 100-ml. volumetric flask and adjust the volume with water. Transfer a 25-ml. aliquot (200-mg. sample) to a 50-ml. beaker. Add 4 ml. of acetone and adjust the volume to 32 =k 2 ml. with water. Determine the pH of the solution and adjust the sample to H 0 70 using 1 to 1 hydrochloric acid solution and water. 8ipet.10 ml. of Alizarin Red S reagent into a 50-ml. volumetric flask and then transfer the sample to the flask. URe the hydrochloric acid-water solution, pH 0.70, for all rinsings and any
