EXCHANGE 9061 '12 *A *M ' soig THE UNIVERSITY OF CHICAGO The Diffusion of Gases and the Density of Chlorine A Search for Probable Isotopes of Chlorine A DISSERTATION SUBMITTED TO THE FACULTY OF THE OGDEN GRADUATE SCHOOL OF SCIENCE IN CANDIDACY FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CHEMISTRY BY William DeGarmo Turner TABLE OF CONTENTS Outline I Introduction 2 Historical 3 The Choice of a Method 5 Description of the Apparatus 6 Manipulation 7 Corrections . 8 Results 13 Summary 14 EXCHANGE THE DIFFUSION OF GASES AND THE DENSITY OF CHLORINE A Search for Probable Isotopes of Chlorine OUTLINE A study of chlorine, to account for its atomic weight of 35.46, was made through the medium of fractional diffusion as a means of separat- ing possible isotopes. To investigate the method and determine its ap- plicability a preliminary investigation was made with the gases Methane (molecular weight about 16) and Ammonia (molecular weight about 17). These gases proved to be separable by means of a diffusion ap- paratus devised for the occasion. Moreover a diffusion of lead nitrate in water solution was made also, to study this type of diffusion as per- haps applicable to chlorine. The method of gas diffusion was chosen and a system designed using as a diffusion medium clay pipe stems, which had proved to be the most desirable of a number of materials considered. The chlorine was subjected to fractional diffusion in this system and density determina- tions were made on both the end fractions. For these determinations a number of density bulbs were prepared and calibrated. A Balance was specially adjusted for the weighings and was enclosed in a large glass case designed to protect it from sudden changes of temperature. To determine gas pressures accurately a precision barometer described by A. O. F. Germann, was constructed and this also was enclosed in a glass case. For final density determinations two volumeters were made and to purify the chlorine for these, precipitated gold was employed in a glass tube heated by a specially designed electrical unit Several preliminary results were obtained all serving to indicate re- finements and improvements to be made in the method of diffusion and density determination. The final densities after the equivalent of 1,024 fractionations and after careful purification are as follows: I. The heavy fraction 3.209 g. per 1. average. II. The light fraction 3.203 g. per 1. average. These results indicate that chlorine cannot be separated into its iso- topes by diffusion of chlorine gas, but suggest the diffusion of Hydro- chloric Acid gas and atomic weight determinations by analytical methods. 559 4 7G 2 THE DIFFUSION OF GASES AND THE DENSITY OF CHLORINE INTRODUCTION Recent studies of the periodic system of the elements, lt 2> 3 and the more perfect formulation of the relationships between the atoms, especially those of atomic weight below 59.0, i. e., the first twenty-seven elements, have led to the recognition of certain hitherto unexplained peculiarities of certain elements. Among these is chlorine with atomic weight 3546 and in a study of its atomic weight the investigation de- scribed in the following pages was undertaken. It has been shown 2 that for the elements up to Cobalt at least, the average deviation of the atomic weight from whole numbers is ex- tremely small on the basis of oxygen = 16, and of these first twenty- three elements Magnesium 24.32 and chlorine 35.46 are the only ones which show large departures. Again the determinations of the weight of the liter normal, of chlorine 4 have given the value 3.214 grams per liter and this value leads to an atomic weight of 35.28 much lower than that obtained by chemical or physical methods, i. e., 35.46. This irregularity also has lead to many attempts at an explanation, for example, by assuming a partial dissociation of the chlorine at ordinary temperatures. This as- sumption however has been shown to be improbable by M. Maurice Pellaton in a careful determination of the physical constants of chlorine 5 leading to the conclusion that there is neither dissociation nor associa- tion in chlorine gas. Moreover, E. Marchand has determined the sur- face tension of liquid chlorine and is lead to the conclusion that chlorine is normal in the liquid state also. It has been recognized in recent years that many elements exist in isotopic forms, i. e., that one element, an identity chemically, and with a single atomic number and so far as is known, a single spectrum, may arise from several independent sources and thus consist of several dif- ferent kinds of atoms with different atomic weights or indeed with the same atomic weight and different intrinsic internal energies. But though these isotopes are the same chemically, they may differ in physical prop- erties such as density or melting point. Thus Richards 6 has shown that 1 Harkins and Wilson, Proc. Nat. Acad. Set., Vol. I, p. 276, May, 1915. 2 Harkins and Wilson, /. A. C. S., 37, 1,367, June, 1915. 3 Harkins and Hall, /. A. C. S., 38, 109, Feb., 1916. 4 Jaquerod and Tourpaian, /. Chim. Phyx., 11, 3 and 269 (1913). , B M. Maurice Pellaton, /. Chim. Phys., 13, 426 (1915). 6 T. W. Richards, 7. A. C. S., 38, 221 (1916). THE: DIFFUSION OF CASKS AND THE: DENSITY OF CHI/DRINK 3 lead from radium has a different density from ordinary lead, and Soddy 7 has shown the same for lead from thorium and ordinary lead. In an entirely different type of investigation (dependent however on the same physical property, density) F. W. Aston in conjunction with Sir J. J. Thompson has attempted the separation of neon by fractional diffusion, into two isotopes. In the light of all these considerations it seemed probable that ordi- nary chlorine must be a mixture of isotopes of different atomic weight and that it should be separable into its constituent parts by diffusion. Such an investigation should be the more valuable since the atomic weight of chlorine is so fundamentally important, especially as the basis of other atomic weight determinations. HISTORICAL Many methods have been used for the study of gas diffusions but few are adapted to the separation of gases by fractional diffusions. One of the early workers was Loschmidt 8 but he conducted his experiments without the use of porous media simply diffusing one gas directly into another. Later Winkelmann 9 and Obermayer 10 have made extended investigations but they studied the speed of diffusion in long narrow tubes. J. Stephan 11 also one of the early investigators followed Loschmidt in sim- ilar work. More recently Ramsay and Rayleigh 12 have used a porous clay pipe for fractional diffusion of atmospheric nitrogen, and Ramsay and Collie 13 and Ramsay and Travers 14 have applied the same methods to clevite gas. Their system was to allow the gas mixture to diffuse from approximately atmospheric pressure into a vacuum so that there probably was an effect due to effusion as well as the diffusion effect. Since pure effusion does not aid in the separation of gases, 15 an ap- paratus designed to make use of the diffusion only would ^eem to have some advantages over other types. 7 Frederic Soddy, "The Chemistry of the Radio Elements," II. 28. 8 Loschmidt, Wien. Ber., 61, (2), 367 (1870); Wlen. Ber., 62, (2), 468 (1870). 9 Winkelmann, Wied. Ann., 22, i, 152 (1884); Wied. Ann., 23, 203 (1884); Wied. Ann., 26, 105 (1886); Wied. Ann., 33, 445 (1888); Wied. Ann., 36, 92 (1889); Ann. Phys., Q, 104 (1901); Ann. Phys., 8, 388 (1902). 10 V. Obermayer, Wien. Ber., 81, (2) 1,102; Wien. Ber., 85, (2) 147, 748 (1882); Wien. Ber., 96, (2) 546. 11 J. Stephan, Wien. Ber., 63, (2) 63. 12 Ramsay and Rayleigh, Phil. Trans., 186, 187 (1895). 13 Ramsay and Collie, Proc. Roy. Soc., 60, 206. 14 Ramsay and Travers, Proc. Roy. Soc., 60, 206. 15 M. W. Travers, "The Experimental Study of Gases," p. 279. 4 THE; DIFFUSION OF GASES AND THE; DENSITY OF CHLORINE Chlorine has been the basis of much careful study particularly from a physical standpoint, since it offers some peculiarities and since it is so abundant and fundamental an element. The atomic weight of chlorine has been determined by many investi- gators using a number of methods : Dixon and Edgar, 16 by direct union of chlorine with Hydrogen, Edgar 17 alone by the same reaction chlorine and Hydrogen but different procedure, Noyes and Weber 18 also by direct union of Hydrogen and chlorine, Guye and Fluss 19 by evolution of chlorine from nitrosyl-chloride, Guye and TerGarzarian 20 by density and critical constants of Hydrochloric Acid, Gray and Burt 21 by a similar physico-chemical study of Hydrochloric Acid, Rich- ards by production of Silver Chloride and Ammonium Chloride, and Baume and Perrot 22 determined it by combining Ammonia gas and Hydrochloric gas. These methods, all either chemical or dependent first of all on a chemical combination lead to a value about 35.460. The density of chlorine has been determined by L,educ, 23 Moissan and Binet, 24 and Jaquerod and Tourpaian 25 as 3.214 grams per liter normal. This will give 35.28 as the atomic weight of chlorine. Mention has been made of the work of Mr. Pellaton 26 one of the most recent works on chlorine constants. This investigator has de- termined the critical temperature, 144, the vapor tension of liquid chlorine from 100 to 144, the density of liquid chlorine, and sat- urated vapor at 7&9 to 144, and latent heats of vaporization. In all of these determinations the chlorine is shown to obey the laws for nor- mal gases. The surface tension of liquid chlorine has been investigated by E. Marchand 27 and he too finds it to be a normal liquid. 16 Dixon and Edgar, Phil. Trans., 205, 169 (1905); Dixon and Edgar, Proc. Roy. Soc., A., 76, 250 (1905). "Edgar, Phil. Trans., 209, i (1908). 18 Noyes and Weber, 7. A. C. S., 30, 13 (1908). 19 Guye and Fluss, 7. Chim. Phys., 6, 722 (1908). 20 Guye and TerGarzarian, C. R., 143, 1,233 (1906). 21 Gray and Burt, 7. C. S., 95, 1,633 (1909). 22 Baume and Perrot, Arch, des Sci. phys. and Nat., (4), 32, 249 (1911); Arch, des Set. phys. and Nat., (4), 34, 352 (1912); 7. Chem. Soc., II, 102, 933; C. R., 155, 461 (1912). 23 Leduc, C. R., 125, 571 (1897). 24 Moissan and Binet, C. R., 137, 1,198 (1903). 25 Jaquerod and Tourpaian, 7. Chim. Phy., 11, 3 (1913). 26 M. Maurice Pellaton, 7. Chim. Phys., 13, 426 (1915). 2T E. Marchand, 7. Chim. Phys., 11, 573. THE; DIFFUSION OF GASES AND THE DENSITY OF CHLORINE 5 THE CHOICE OF A METHOD The method to be chosen for separation of possible isotopes should depend on diffusion since the speed of diffusion of gases varies with the molecular weights. Furthermore diffusion has been attempted in such a separation in the case of neon by Aston, 28 as has already been noted. Diffusion of a salt in solution might also effect, a separation but this method is less rapid. In order to test the speed of separation of gases of nearly the same molecular weights investigation was conducted on the rate of separation of the gases, Methane (atomic weight 16) and Am- monia (atomic weight 17). The rate of diffusion of a lead salt in aqueous solution was also investigated. The results of these investigations showed that gas diffusion is moderately rapid since a mixture of approximately equal volumes of Methane and Ammonia may be diffused by a process consuming only a few days until the remaining mixture contains about twelve times as much Ammonia as Methane. On the other hand a lead solution after more than a year had diffused upward through twenty-five centimeters of water only enough to give a negligible concentration at the top. Accordingly the method of gas diffusion through porous material was adopted. In principle such a separation might be conducted after a scheme similar to that used in fractional crystallization where a con- stantly increasing number of simultaneous separations are carried on by successive combinations of each light with its neighboring heavy fraction. However when an ample supply of the elementary material is at hand, the intermediate portions may be discarded and only the end fractions retained. Now in a separation by diffusion the heavier constituent will tend to remain within the porous tube while the lighter will pass through the wall in excess. The gas from within may then run through a second tube, what passes through the wall may be discarded as an inter- mediate fraction and what remains may be sent through a third and fourth, 36 was not made be- cause the gas was referred to water as a standard by the method of de- termination employed. When the density of a gas is referred to that of water, then if the density of water is given in terms of its weight at sea level and 45 N. lat., the density of the gas will also be so ex- pressed without further correction. Such a correction is made by Ger- mann for instance. 34 In his case the density of water is taken as 0.999868, a value which is referred to the weight of water at four degrees C. as i.oooooo. 37 The correction to be applied for location should therefore have been referred to the altitude and latitude of that place where water has an absolute weight of i.oooooo grams at four degrees C. If in- stead of 0.999868, the absolute density of water had been taken, i. e., the density expressed in terms of the weight of one centimeter of water at zero degrees C at forty-five degrees N. latitude and sea level, then no correction would have been necessary. 84 Germann, 7. Phys. Chem., 19, 472 (1915). 35 Guye, 7. Chim. Phys., 5, 203 (1907). 86 Gray and Burt, 7. Chem. Soc., 95, 1,636 (1909). 87 Thiesen, Wiss. Abh. Phys.-Tech. Reich, 3, 68 (1900). THE DIFFUSION OF CASKS AND THE DENSITY OF CHLORINE II This correction may be considered further. The reductions to forty- five degrees N. latitude and sea level, of weighings made by counter- balancing with a set of standardized weights should be dependent upon the way in which the set has been standardized. If it has been checked against weights which are correct at forty-five degrees N. latitude and sea level, then it will give results wherever it is used which are also standard at forty-five degrees N. latitude and sea level, for whatever mass will counterbalance a given weight in one location will counter- balance the same piece in any other location. Furthermore, if the set has been checked against weights standard at some location other than forty-five degrees N. latitude and sea level, then that location is the one to use in making corrections to absolute weight, and not the location in which the set happens to be used. The same reasoning applies to weights of gas which are referred to corresponding weights of water. If the water weight is correct at sea level, etc., i. e., if its absolute density is taken, then the absolute density of the gas is given without correction. For example, suppose a gas is weighed in a given flask in some location, and suppose the flask is cali- brated with water using the same set of weights, which need not be standard but must be relatively correct. 38 Call the weight of gas at zero degrees C. for simplicity A, and the weight of the water in the same volume at zero degrees C. 800 A. Then at zero degrees C. the gas weighs as much as water in the given location. It will also weigh . as much at forty-five degrees N. latitude and sea level oOO and if absolute density of water is used in the calculation then absolute density of the gas will be given directly. Furthermore if absolute den- sity has not been used the necessary correction to sea level will be de- pendent only on the value of density which has been accepted and will be independent of the location in which the investigation is made and of the particular weight-pieces used. C. Considering next the corrections for the weight of the density bulbs of chlorine. i. The first correction is for buoyancy of the air on the weights used. Since the bulb is counterpoised, the only correction is for the change in W weights and is given by, - x 0.00120 where W is the weight used, *5 the 0.00120 is the density of air and 8.5 is the density of brass. This cor- 38 Gray and Burt, 7. Chem. Soc., 95, 1,636 (1909). 12 THE DIFFUSION OF GASES AND THE DENSITY OF CHLORINE rection applies to all weights whether of brass or not, since they were all calibrated against a brass standard. 39 This must be subtracted since the actual weight added to replace the chlorine is less by this amount than the face value of the weights. 2. The second correction is for the contraction of the bulb on evacua- tion. This is equal to the weight of air displaced when the bulb expands and is therefore given by S x 0.00120 where S is the change in volume. This must be added to the weight since the bulb in buoyed up by less air and therefore weighs too heavy when evacuated. 3. The third correction is for the residual chlorine. This may be computed as a pressure by means of the formula = x P and applied as a correction to be subtracted from the pressure of the chlorine or it may be computed in weight by means of the formula 0.003214 x 27 T> P ' x - x V and added to the weight of the chlorine. Since it 1 700 varied somewhat from time to time it was found convenient to com- pute it as a pressure thus avoiding a separate computation for each in- dividual bulb. 4. The fourth correction is for the compressibility of the chlorine, that is for its deviation from a normal gas within the range of the pres- sure change involved in the computation of the weight of the liter nor- mal. This pressure change was never great, from 760 to about 745 usually, but might be applied either in the computation of the true volume or as an additive correction after the computation was made. D. Only one correction was applied to the weight of the ampoule. This was for the buoyancy of the air, and since the ampoule was weighed without counterpoise the correction was applied both to the weights and to the ampoule. The correction may be represented by the formula W = W o + S(V s - V w ). Where W is correct weight, W o ob- served weight, d density of air, V s and V w the volume of the sub- stance and of the weights, now V - for brass calibrated weights 8 -5 and V may be computed from the weight of the ampoule in air (W a ) and in water (W w ) by the formula - - V f =W a - W w with suf- ficient accuracy. Then using the average value for d as 0.00117, the for- mula reduces to - - W = 1.001032 W a 0.00117 W w . This cor- rection was applied both to the full and empty ampoule. 39 Gray and Burt, J. Chem. Soc., 95, 1,636 (1909). THE DIFFUSION OF CASKS AND THF, DENSITY OF CHLORINE RESULTS Results of all Determinations are Tabulated Below : TABLE I. CALIBRATION OF BULBS. Bulb Mo. Weight of water, first Weight of water, second Volume first Volume second I II III IV 310.549 677.906 889.570 678.173 310.529 889.554 678.137 310.556 677.920 889.587 678.186 310.536 889.571 678.150 TABLE II CONTRACTION BY METHED OF RAYLEIGH Bulb No. I II III IV Volume 310.546 677-920 889.579 678.168 Contraction 0.0025 0.0105 0.006O 0.0005 TABLE III. DENSITY AFTER FIRST SERIES. Bulb Corrected barometer Corrected weight Corrected weight True weight of Weight per liter millimeter evacuated full chlorine normal I a 752.51 1.8906 0.9040 0.9864 3.208 b 752.51 2.6926 0.5530 2.1393 3.187 II a 748.11 1.8901 0-9337 0.9562 3-201 b 748.11 2.6922 0.5469 2.1450 3-214 c 748.11 34913 0.6807 2.8 IO2 3-209 TABLE IV. DENSITY AFTER SECOND SERIES. Bulb Corrected barometer Corrected weight Corrected True weight weight of Weight per liter millimeter evacuated full chlorine normal I a 746.74 1.8904 0.9147 0-9755 3-197 b 746.74 34918 0.6864 2.805O 3-209 II a 746.34 1.0960 0.9321 0.9742 3-195 b 746.34 2.6973 0.5627 2.1350 3.206 c 746.34 3.5025 0.7054 2.7975 3.202 TABLE V. DENSITY AFTER COMBINED SERIES, REFINED APPARATUS HEAVY FRACTION ONLY. Bulb Corrected barometer millimeter Corrected weight evacuated Corrected weight full True weight of chlorine Weight per liter normal I II III 746.09 746.09 746.09 1.8912 2.6930 3-4920 0.9129 0.5561 0.6908 0.9781 2.1366 2.8008 3.2084 3.2092 3.2072 14 THE DIFFUSION OF GASES AND THE DENSITY OF CHLORINE TABLE VI. DENSITY AFTER COMBINED SERIES, REFINED APPARATUS, LIGHT FRACTION ONLY. Ampoule Corrected volume of apparatus Corrected weight of ampoule full Corrected weight of ampoule empty Corrected barometric pressure Weight per liter normal I II 1408.779 1423-731 23.8677 23.0346 19-4477 18.5730 742.49 742.00 3-2019 3.2037 The above results may be summarized showing the heavy fraction to average 3.208 grams per liter, and the light fraction to average 3.203 grams per liter. The conclusion to be drawn from these results is that chlorine as a gas cannot be separated into its isotopes by diffusion. This is probably due to the fact that the gas molecules in chlorine consist of combinations of both lighter and heavier fractions, as well as combina- tions of two atoms of the lighter or two atoms of the heavier. A further conclusion may be drawn that density determinations involve great dif- ficulties in manipulative technique. A preliminary experiment on the diffusion of methane and ammonia, however, has shown the reliability and ease of separating two gases of slightly different density by diffusion. A continuation, therefore, of this investigation will involve the fractional diffusion of hydrochloric acid gas and the determination of the weight of its chlorine content by gravimetric and volumetric analytical methods. SUMMARY Since the atomic weight of chlorine shows some irregularity when con- sidered in the light of formulae recently developed in a study of the periodic system, an attempt was made to account for this abnormality. The chlorine was subjected to a series of fractional diffusions in a specially designed apparatus and the density of the end fractions was determined. Preliminary density determinations were made from time to time with a refined type of density bulb apparatus. This proved in- sufficient for the final determinations and for these a special volumeter without stop cocks was employed after taking careful precautions to in- sure a pure chlorine. The results indicate that chlorine cannot be separated into its isotopes by diffusion of chlorine gas, and that density determinations are too tedious as a means of determining atomic weight. An investigation by diffusion of Hydrochloric Acid and analytical determination of atomic weights has since been carried out in this laboratory. 5594 rc" UNIVERSITY OF CALIFORNIA LIBRARY