Kov., 1960
NOTES
GASKETS Teflon PIOStlC
Neoprene
1775
A 30 ton hydraulic jack waa used to obtain the pressures. The press was made from reinforced 8 inch channel iron welded in the shape of a box with two inch threaded stock as supports. A steel shield waa used to cover the front and sides of the press and a heavy wire screen was used in the back. By means of a mirror mounted on the wall behind the press, the pressure cell could be observed during the high pressure tests. The external pressure in all cases was measured by means of a calibrated load cell. This cell consisted of a hardened steel cylinder with two measuring and two compensating strain gauges cemented onto the cylinder walls. The samples were maintained a t constant temperature by thermostats from which oil was pumped to the copper jacketed pressure cell. A cold temperature bath was used to quickly “freeze” the reaction at the end of each experimental run. Various methods were tried to contain the sample while under pressure. Both glass and steel tubes with rubber stoppers a t both ends were tried, but found unsatisfactory. Finally, a very simple procedure gave good results. This consisted of small polyethylene bags containing the sample solution and tied with string. Methyl alcohol was used as the hydraulic fluid. It was found that even under very high pressures no leakage could be detected. All experimental runs were conducted with these polyethylene bags.
Acknowledgment.-We wish to t,hank the Office of Naval Research which provided the funds for this project. We are also indebted to Mr. E. L. Hardy and Mr. Arthur Nettleship who constructed the pressure apparatus as well as Mr. W. J. Teerlink and Dr. J. M. Sugihara who synthesized and resolved the hindered biphenyl.
THE POLL4RIZABILITYOF RADON BYD. G. TUCK Fig, 4.-Diagram
of pressure cell.
cell inside. The seals shown in Fig. 4 were adopted and found satisfactory t o 15,000 atmospheres. In this vessel the plastic chosen for the backup rings waa fabric reinforced phenol formaldehyde sheet. Its shearing strength is ample to contain the softer Teflon. Teflon shows a very low coefficient of friction against most solids, and i t is felt that in this design a thin film of this plastic rubs off onto the steel walls and serves as a lubricant for the phenolic rings. A novel feature of these closures is the use of Neoprene 0 rings, both top and bottom, so placed as to reduce to a minimum the danger of necking off the plugs. The top plug is held in place by means of a concentric screw in the piston while since no movement is required of the bottom plug, the screw is omitted. In the bottom plug the sandwich of Teflon between phenolic rings worked well. It is probable that the top phenolic ring could be dispensed with although some leakage was observed in the instance when i t was tried. Pistons and plugs were of “Venango Special” steel (Uniyersal Cyclops) hardened to Rockwell C52. Fnction was found to be not greater than 5% of the thrust on the top piston. Each pressure measurement was made by raising the thrust until slight movement of the piston occurred, observed by means of a dial gauge. Thi? thrust was recorded. The thrust then %as decreased until again there was movement of the pistons (in the opposite direction) and the reduced thrust was measured. Pressure then was calculated from the average of the two thrusts, and probably was accurate within plus or minus 1%. From observations that will not be recorded here, it was concluded that the main friction between 0 and 4,000 atmospheres was exerted by the 0 rings, but as the pressure increased to the range of 5,000 to 7,000 atmospheres the roefficient of friction decreased indicating extrusion of the low friction Teflon ring. At about 7,000 atmospheres the coefficient of friction again increased, which was interpreted to mean that a t this higher pressure the harder plastic rings had extruded against the cylinder rralls.
Department of
ChemistTy,
University of Nottingham, Nottingham, England Reeezued June 1 , 1960
I n a recent publication, Miller’ has given calculated values for the intermolecular force constants of radon; in the course of the calculatioy, two slightly differing values of 4.50 and 5.86 A.3 are derived for the polarizability of the radon atom. The purpose of the present note is to show that a concordant value of 6.3 for this parameter can be derived by a quite independent method. Chackett and the present author2have measured the heats of adsorption of the inert gases on charcoal a t low equilibrium pressures ( p 5 lop2 mm.). From the results, a value of 13.5 f 1.4 kcal./g. atom was deduced for the heat of adsorption of radon on charcoal under similar conditions; since the periodic behavior of the inert gases is well established (see ref. 2), the limits set on this value are reasonably generous. I n the same paper it was shown that for the experimental conditions of negligible interaction between adsorbed atoms, there is a good (semi-empirical) linear relationship between the heat of adsorption (AH) and the polarizability (a), which can be expressed as AH = 0.29
+ 2.11~2
where AH is in kcal./g. atom and a is cm.a. Substituting the above value of AH for radon into this equation gives THISJOURXAL, 64, 163 (1960). (2) K. F. Chackett and D. G . Tuck, Trans. Faraday S o r . , 63, 1632 (1957). (1) G . A. Miller,
NOTES
1776
Vol. 64
I n the same range of pH and of concentrations of Cr(I1) and oxalate, but with the Cr(I1) and oxalate in approximately equimolar amounts, the AH. The agreement with the higher of the t,wo values initial rapid reduction of oxalate is soon inhibited calculated by Miller is extremely good considering by the formation of Cr(II1)-oxalato complexes. The tailing off in the rate of Cr(I1) consumption is the extrapolations involved. illustrated by the following typical result. In a solution which was initially 0.975 X 10+ M in Cr+2and 1.00 X M in oxalic acid, and which THE REDUCTION OF OXALATE BY had a pH of 1.6,' 29% of the Cr(I1) was oxidized CHROMIUM(II)'b2 after 6 minutes, but only 51% after 10 hours. The BY RONALD M. MILBURN AND HENRY TAUBE amount of oxalate reduced by the initial fast reaction can be greatly increased by introduction into Georee Herbert Jones Laboratoru, Universatj of Chicago, Chzcago, Illznozs the solution of other chelates, such as pyrophosRecewed June 3. 1960 phate or ethylenediaminetetraacetate, which, while It has been shown that free oxalate is rather ra- not reduced by Cr(II),8 compete for coordination pidly reduced to glycolate by solutions of Cr(1I) per- positions on the Cr(II1). In some typical cases chlorate. Oxalate bound to Cr(II1) is reduced only up to 70% reduction of Cr+2 was achieved in the very slowly by Cr(I1). The observation that oxa- first few minutes. late and Cr(I1) undergo an oxidation-reduction Experimental reaction is in agreement with M ~ i s s a n who , ~ reOrdinary distilled water was further purified by refluxing ported that on preparation of Cr(I1) oxalate, part with alkaline permanganate for about 12 hours, and redistilling from a tin apparatus. Solutions of Cr+2 and Cr.,+3 of the Cr(I1) was always oxidized. prepared by standard methods.9 Except where otherWe find that in the pH range 1-2, with oxalate in were wise indicated, perchlorate was used as the anion in solutions. moderate excess over Cr(I1) and with concentra- Reactions of Cr f 2 were conducted a t room temperature tions of the order of 1/100 AI, most of the Cr(I1) is (-23") under an atmosphere of nitrogen. Concentrations oxidized within a few minutes a t room temperature. of Cr+2 were estimated by addition of a deaerated solution of excess iodine (prepared as needed from standard iodate, The Cr(II1) produced is violet-red, of similar and iodide and acid) followed by potentiometric titration of color to Cr(III)-oxalato complexes. Some tailing the remaining iodine with thiosulfate, using platinum and off in the rate of Cr(I1) consumption is observed. calomel electrodes. Glycolate was determined quantitatively by addition to 1 In a solution which was initially 1.77 X loT2M of solution, !.5 X 10r4.to5.0 X M in glycolate, of in Cr+2 and 9.1 X 10-2 AI in oxalic acid, and which ml. 10 ml. of a solution containing 0.01 g. of 2,7-dihydroxynaphhad an initial pH of 1.2, the consumptions of Cr(I1) thalene per 10 ml. of concentrated sulfuric acid. The resultat -23" were: t = 0, 0%; t = 0.10 hr., 91.4%; ing sample was heated for 1 hour at 90" together with samt = 1.0 hr., 91.2%; t = 24 hr., 97.2%. A solution ples prepared from a solution of known concentration in glycolate. On cooling the solutions the optical densities at 540 of the same composition was allowed to react to mp were measured and compared. Beer's law was found to essential completion (> 98% Cr(I1) oxidized), be obeyed throughout the specified concentration range. and then was exposed to the atmosphere, heated before the potassium hydroxide treatment failed to reveal with potassium hydroxide to free ligands attached solution of free glyoxal. to the Cr(III), and filtered while hot and again after the(7)presence This solution was buffered with HSOd- and SO'-5 Similar cooling in an ice-bath.* Tests made on portions of tailing off was observed with unbuffered solutions. (8) Although some oxidation of Cr(I1) by ethylenediaminetetraacet,he filtrate to determine the nature of the reduced tate was observed, the amount of oxidation in a few minutes was negspecies gave no indication of chloride, formate, ligible. formaldehyde, glyoxalate or glyoxal, but gave posi(9) H. Taube and H. Myers, J . Am. Chem. Soc., 1 6 , 2103 (1954). tive evidence for the presence of glycolate by the deep red-violet color of the 2,7-dihydroxynaphthalene test.5 Comparison of' the absorbance a t T H E HEAT OF COMBUSTION OF 540 mp of the red-violet product with the absorDICYANOBCETYLENE bancies given by solutions of known glycolate conBYGEORGE T. ARMSTRONG AND SIDNEY MARANTZ centrations indicated that the original filtrate conThe National Bureau of Standards, Washington, D . C. tained 95% of the amount to be expected for quanReceived June 6 , 1060 titative reduction of oxalate to glycolate by the Cr(I1) .'j Cyanogen, dicyanoacetylene and the dicyano(1) Supported by the A.E.C. under Contract AT(ll-1)-378. polyacetylenes are highly unstable thermodynami(2) The observations reported were made in the course of a study of cally. When they are burned with the proper the catalysis b y C r + + of the formation of Cr(II1) complexes. Alproportions of oxygen, carbon monoxide and though the research failed in its purpose with oxalate as ligand, a nitrogen may be the principal products of comstriking effect was demonstrated with pyrophosphate as ligand. (3) H. Moissan, Compt. rend., 92, 1051 (1881); Ann. chim. et p h y ~ . , bustion. These facts lead to the possibility of [5] !Xi, 401 (1882). obtaining very high temperatures of combustion, a (4) Much of the perchlorate was removed as KClO4; large amounts possibility which has been borne out by experiments of perchlorate interfered with some of the tests made. of Conway, Smith, Liddell and Grossel on the ( 5 ) On acidification with nitric acid and addition of silver nitrate, no cloudiness from silver chloride was observed. The qualitative combustion of cyanogen. Kirshenbaum and tests for the organic compounds were taken from F. Feigl, "Spot Testa Grosse2have calculated that even higher temperain Organic Analysis,"' D. Van Nostrand Co., Inc., Princeton, N. .I., QR,, =
6.3 f 0.6
where the limits are those of the derived value of
5th edition, 1954. (6) The potasaium hydroxide treatment may have resulted in at least partial conversion of any glyoxal to glycolate. Tests on the
(1) J. B. Conway, W. F. R. Smith, W. J. Liddell and A. V. Grosses J . Am. Chem. Soc.. 17, 2026 (1955). (2) A. D. Kirshenbaum and A. V, Grosse, ibid., 78, 2020 (195D).
