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The effect of helium on the dissociation of hydrogen in the high frequency discharge and the adsorption… Munro, Ferdinand L. 1930

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U . B . C . CAI. ^  THE EFFECT OF HELIUM ON THE DISSOCIATION OF HYDROGEN IN THE HIGH FREQUENCY DISCHARGE and THE ADSORPTION OF HYDROGEN BY SULPHUR b y Ferdinand L. Monro  A Thesis submitted for the Degree of MASTER OF ARTS in the Department of CHEMISTRY  THE UNIVERSITY OF BRITISH COLUMBIA April, I93O.  U 8 R A R Y  TABLE OF CONTENTS  Page. Previous Work  1.  Object of Present Investigation  2.  Apparatus  3*  Diagram of Apparatus  (to face) 3 .  Experimental  4.  Results  6.  Discussion of Results  6.  Summary  8.  Tables  10 to 1 5 .  THE EFFECT OF HELIUM ON THE DISSOCIATION OF HYDROGEN IN THE HIGH FREQUENCY DISCHARGE.  Previous Work. The first mention of dissociation due to electrical discharge was that by S. P. Farwell,^ who in 1^14 reported an increase in pressure for the corona discharge in air. increase in pressure was ascribed 2 various causes.  In 1<?1& Kunz  This  by different workers to  came to the conclusion that the  effect was not due to heating, but that it was due, at least partially, to ionization.  The following year Arnold^ ascribed  the pressure increase to heating effect alone.  After  com-  paring the increase in pressure due to heat and that due to the corona, Warner^ came to the conclusion that the initial effect in the corona was due to ionization.  In 1?18 Tyndall^  published a paper supporting Arnold's view, but in lp20 Fazel^ concluded that the pressure effect was due to ionization and not heat.  The same year Kunz^ ascribed the  pressure increase to the fact that the ions impart their momen to the gas. 1. Farwell, Proc. Am.I E.E. 33, 16^3 (1?14); Phys. Rev. 4, 3 1 (1914J 2. Runz, Phys. Rev. _8, 28 (1?16) 3. Arnold, Phys. Rev. 93 (l^l?) 4. Warner, Phys. Rev. F , 285 (l^lb); 10, 483(1917) 5. Tyndall, Phil. Mag.**33, 261 (1^18) 6. Fazell, Phys. Rev. 1*^* 157 (1?22) 7. Kunz, Phys. Rev. 19, 163 (1^22)  -  2  -  In 1929, Marshall & Nunn^ reported work that had teen carried on at this University for the past five years on the effect of high frequency discharges on the dissociation of various gases,  in it they definitely showed that the increase in  pressure due to electrical discharges was caused by dissociation of the gas.  They determined the dissociation for  different gases, by noting the almost instantaneous pressure increase when the discharge was passed.-  The dissociation was  found to increase with increase in pressure.  It was also  found that the dissociation depended on the dimensions of the discharge tube. Object of the Present Investigation. In their paper Marshall & Nunn showed that helium gave no pressure increase corresponding to that of dissociation. This is to be expected since ordinary atomic dissociation is impossible in a monatomic gas.  It was thought, however, that  the helium might have some effect on the dissociation of a diatomic gas, as an activating agent or as a mechanical agent by preventing the recombination of the atoms when once dissociated. With the object of determining this effect, it was decided to mix hydrogen and helium in varying proportions and compare the pressure increase with that obtained for corresponding amounts of pure hydrogen.  Since this pressure in-  crease would be due only to dissociation of the hydrogen, the effect of the helium could be easily found. 1.  Trans. Am. Electrochem. Soc. 40, 11^ (1^2?)  - 3 Apparatus. The apparatus used for this work was used by Marshall and Nunn.  similar to that  The discharge tube used was the  tube described in their paper and consisted of a pyrex tube 2.3 cm. in external diameter and 27 cm. long.  The ends were  covered with foil 6 cm. deep, leaving the edges 15 cm. apart. The volume of the tube was ^2.^4 cm.  The hydrogen was pre-  pared by the electrolysis of a saturated solution of Ba(0H)2 and dried by passage over calcium chloride and phosphorous pentoxide. The helium was purified by passing it through a tube of activated charcoal (B) which had been freed from gases by heating it, in a vacuum, to 444° in the vapor of boiling su!phur.  The pressure of helium passing through the charcoal  was controlled by means of the manometer (G).  This consisted  of a mercury manometer with the air left in the sealed arm. The large bulb on the other arm was used as a reservoir for the mercury when the apparatus was pumped out.  By means of  this manometer the helium pressure could be kept at about one atmosphere.  The overflow manometer (K) was used to permit  the escape of gas from the charcoal tube when the liquid air was removed.  The purified helium was stored in a reservoir  (L) containing phosphorous pentoxide to remove any traces of moisture.  The current was supplied by an Oudin oscillation  transformer (H) operated by a transformer (E).  K.W. 10,000 volt wireless  The spark gap (S) and condenser (F) were  - 4 included in the circuit as shown.  The current was measured by  a Weston Thermo Galvanometer (N) placed in the ground lead. The current was kept nearly constant at about  m.a.  Experimental The main difficulty is to distinguish between the increase in pressure due to dissociation and that due to heating.  After trying various methods, it was found that the most  consistent results were obtained if the current was left on for a few seconds after the initial increase in pressure due to the dissociation had taken place, and then  a reading of  the level on the left side of the manometer was taken. same time the current was turned off.  At the  The manometer level  immediately dropped very rapidly for one or two seconds and then much more slowly.  The reading when the change in rate  occurred was taken and the difference between this and the initial reading was taken as half the increase in pressure due to the dissociation. Experiments were first made with helium in order to determine whether it gave any increase in pressure corresponding to that given by a diatomic gas.  It was found that the  pressure increased from 4-3% but that the increase lessened as the pressure increased instead of increasing with pressure as found for hydrogen by Marshall & Nunn. The method used in determining the effect of the helium on the dissociation of hydrogen was as follows: Hydrogen was admitted to the discharge tube, the pressure  noted and the dissociation determined as described.  Helium  was then added to the hydrogen in increasing quantities and the dissociation determined after each addition.  The apparatus  was then pumped out and a new series of readings were obtained for a different initial pressure of hydrogen. The actual dissociation was calculated from the results obtained by means of the formula given by Marshall and Nunn.  where p^ - initial pressure of gas r pressure of hydrogen. (P2**Pl) * increase in pressure due to dissociation. Vb - volume of discharge tube. V^ - volume over the manometer and the connecting parts before passing the discharge. A ? I increase in Va due to the depression in the sulphuric acid level when the discharge is passed. The values of the constants in the above equation for all series except that given in table 3 were Vb I 92.94 c.c. = 7 . 2 c.c. + (77-R).i234 where R was the reading on the right hand side of the manometer at the pressure under consideration.  While obtaining  the values for series 6 it was found that the discharge tube had developed a weak spot that was continually puncturing. For  series 3 it was replaced by another tube of the same  linear dimensions but having a volume of 88.24 c.c. other constants were kept the same.  The  Results The results obtained for various hydrogen pressures are given in tables 1-3. and those for helium alone in table 6. Pressure readings are given in centimeters of sulphuric acid (density I.834) as measured, and also converted to millimeters of mercury, 1 em. of sulphuric being equal to 1.355 mm. of mercury.  The first column gives the pressure of helium added  to the pressure of hydrogen given at the top of the table, the second the increase in pressure for the corresponding mixture and the third the % dissociation, caluclated on the basis of the hydrogen present.  The current is given in the fourth  column. The results for the various hydrogen - helium mixtures are plotted in the graph.  Each curve gives the %  dissociation for the indicated pressure of hydrogen in the presence of the pressure of helium shown on the abscissa. It will be noted that the dissociation of a fixed amount of hydrogen increases almost linearly with the amount of helium added.  The slope of the various curves decreases  with increasing amounts of hydrogen, showing that the effect of a fixed amount of helium decreases as it is added to increasing amounts of hydrogen. Discussion of Results. The theory of the vacuum tube is very complicated but results obtained may, at least partially, be ascribed to the following causes.  1.  Activation of the Helium.  1.  It has been shown by various workers that helium has the effect of dissociating nitrogen molecules into its neutral atomic form.  This is due to the nitrogen becoming excited by  impacts of the second kind with metastable helium atoms. Since it is known that hydrogen can only be dissociated into neutral atoms by collisions of the second order, an explanation of the dissociation of the hydrogen both alone and in the presence of helium, will be found in the following considerations. With pure hydrogen the view is that a hydrogen molecule becomes activated and then by a collision of the second kind with another molecule transmits sufficient energy to the second molecule to dissociate it into two neutral atoms.  The  excess energy is most probably emitted as light or may be used in dissociating the original molecule into a charged and a neutral hydrogen atom. The helium plays the same part in mixtures as the first hydrogen atom does in pure hydrogen.  In this case,  besides the action of the hydrogen on itself, the helium atoms are raised to a 20.5 volt level by direct electron impacts. These metastable atoms then collide with neutral hydrogen molecules and. dissociate them into neutral hydrogen atoms. Since the heat of dissociation of hydrogen into neutral atoms corresponds to 3.5 volts it can be seen that this theory 1.  Merton and Pilley Duffendack & Wolf  Roy. Soc. Proc. A107 411,1925. Phy. Rev. J54 4097*1^29.  satisfactorily explains the action of the helium. In mixtures of hydrogen and helium there is, therefore, added to the normal effect due to hydrogen collisions, the effect of collisions between hydrogen molecules and activated helium atoms. 2.  Effect of Helium on Recombination of Hydrogen. Besides the dissociating effect discussed above  the helium also has a mechanical effect of decreasing the mean free path of the dissociated hydrogen atoms and thereby decreasing the rate of recombination.  It is difficult to  estimate the extent of this effect since it is superimposed on the dissociating effect of the helium. The results obtained are most probably due to a combination of the two causes discussed above, with the dissociating effect of the helium predominating. SUMMARY 1.  The effect of helium on the dissociation of  hydrogen in the high frequency discharge has been studied and it is found the helium has the effect of increasing the dissociation. 2.  The increase has been ascribed to two causes, i. ii.  The dissociating effect of the helium. The decrease in the rate of recombination of hydrogen atoms due to the presence of the helium.  The first effect is thought to be the predominating cause.  - 9 In conclusion I wish to express my appreciation to Dr. M. J. Marshall for his unfailing help and advice in both the practical and theoretical aspects of this investigation.  UBC Scanned by UBC Library  - 10 -  TABLE I  Hydrogen r 46.3 cm* HgSO, = 62.7 Mm. Hg.  Helium Cm. H2SO4  Pressure Increase  Current  Mm. Hg.  Cm. H2SO4  Mm. Hg.  %  0  0  7.2  9.7  19.4  84  2.3  3.1  7.5  10.2  19.9  93  4.3  5.8  7.9  10.7  21.2  93  7.8  10.5  8.4  11.4  22.6  93  8.9  12.1  9.0  12.2  24.6  91.5  12.9  17.5  9.6  13.0  26.4  92  16.6  22.5  10.2  13.8  28.1  91.5  18.9  25.6  10.6  14.4  29.3  92  21.9  29.6  10.8  14.5  30.0  91.5  25.4  34.4  11.2  15.2  30.8  91.5  28.6  38.7  11.8  16.0  33.2  91.5  M. A.  - 11 TABLE II  Hydrogen = 34.75 cm. HgSO. = 47.08 Mm.Hg. Pressure Increase  Helium  Current  Mm. Hg.  Cm. HgSO^  Mm. Hg.  %  0  0  5.1  6.9  17.1  85  1.10  1.49  5.4  7.3  17.9  86  3.35  4.54  6.0  8.1  18.1  88  5.60  7.59  6.6  8.9  22.0  89  7.55  10.23  7.0  9.5  22.9  89  9.75  13.21  7.2  9.8  23.8  90.5  11.65  15.78  7.8  10.5  25.0  88.5  13.7  18.56  8.3  11.2  25.2  89  16.6  22.5  8.4  11.4  27.0  89  19.6  26.6  8.6  11.6  28.8  89  21.7  29.4  8.8  11.9  30.1  -  24.0  32.5  9.0  12.2  31.2  87.5  26.3  35.6  9.2  12.5  31.9  88  28.1  38.1  9.5  12.9  33.6  86  30.9  41.9  9.8  13.3  34.2  84  33.2  45.0  10.0  13.5  35.1  86  35.2  47.0  10.2  13.8  35.1  86  Cm.  M. A.  - 12 TABLE III Hydrogen I 24.15 cm. HpSO, = 32.70 Mm.Hg. Helium Cm. HgSO^ 0 2.48 4.57 7.89 28.13 30.25 34.03 35.55 38.38 43.25 45.25  Current  Pressure Increase Mm. Hg.  0 3.68 6.18 10.68 35.03 43.10 46.21 48.18 51.95 ' 53.56 61.25  Cm. H2SO4 3.10 3.40 3.84 4.44 8.96 8.92 9.50 9.42 9.64 10.10 10.42  Mm. Hg. 4.20 4.61 5.20 . 6.01 12.14 12.08 12.87 12.76 13.06 13.68 14.12  %  M. A.  15.2 16.7 19.0 22.0 42.7 46.9 50.7 50.4 51.6 55.5 56.7  103.5 104 102 104 102.5 104 106 106 99  24.2 25.3 26.0 31.0 34.1 34.1 36.1 42.3  99 89 89 88 88.5 88 88 88  TABI,E Illa 7.00 8.45 12.03 17.0 19.8 23.1 26.7 28.2  9.48 14.50 16.30 23.03 26.83 31.30 36.18 38.21  4.8 5.0 5.1 6.0 6.5 7.3 7.6 7.9  6.5 6.8 6.9 8.1 8.8 9.9 10.3 10.7  Note to series Illa While obtaining the values for Table III, a gap was left between the helium pressures 7.9 - 28.1 cm. HgSO,. This series was obtained to fill this gap. Values obtained for series III are indicated by ; those for 111a by . A new resistance wire was used at this point. Apparently it has not been accurately calibrated.  - 13 TABLE IV Hydrogen = 14.62 cm. HgSO^ r 19.81 Mm.Hg.  Cm. EgSO^  Current  Pressure Increase  Helium Mm. Hg.  Cm.HHHgSOg  Mm. Hg.  M. A.  8.7  110  0  1.14  1.54  1.18  1.24  1.68  9.7  110  5.43  7.36  2.04  2.76  16.0  110  7.31  9.91  '2.18  2.95  17.1  104  9.91  13.42  2.60  3.52  20.3  105  10.88  14.72  2.98  4.04  23.6  16.53  22.41  3.66  4.96  29.4  21.25  29.18  4.49  6.08  36.3  23.98  32.48  5.10  6.91  41.1  28.83  39.15  6.22  8.43  51.6  31.80  43.08  6.60  8.94  55.1  103  34.62  46.95  7.10  9.62  59.8  101  CO  0  .  %  106  103  - 14 -  TABLE Hydrogen r  8.85 cm. HpSO^, = 11.98 Hm.Hg.  Helium Cm. H2SO4 0  Note:  V  Pressure Increase  Mm. Hg+ 0  Cm. K2SO4  Mm. Hg.  %  .50  .67  6.5  1.10  * 1.48  .56  .76  7.3  2.17  2.93  .60  .81  7.75  2.88  3.89  .66  .89  8.57  4.70  6.34  .84  1.34  11.00  6.03  8.14  .92  1.24  12.05  8.62  11.63  1.10  1.48  14.37  10.45  14.11  1.24  1.67  16.25  12.00  16.20  1.42  1.92  18.25  13.57  18.32  1.60  2.16  21.00  15.30  20.65  1.82  2.46  24.22  17.20  23.22  1.98  2.67  27.56  19.65  26.53  2.18  2.94  29.30  21.50  29.02  2.40  3.24  32.70  23.06  31.13  2.61  3.52  33.08  24.88  33.59  2.70  3.64  36.38  Owing to leakage in the condenser it was impossible to obtain accurate readings of the current used. It was approximately 90 M.A. for each pressure.  - 13 TABLE VI Hydrogen = 6.92 cm. HgSO^ = 9.34 Mm.Hg.  Cm. K2SO4 0  Current  Pressure Increase  Helium Mm. Hg.  Cm. HpS0„ ^ 4  0  .50  .67  Mm. Hg.  %  M . A.  8.95  91  .61  .82  .58  .78  10.3  91  1.22  1.65  .60  .81  10.7  91  1.75  2.36  .66  .89-  11.8  91  2.68  3.62  .68  .92  12.1  91  3.68  4.97  .80  1.08  13.0  91  5.0?  6.84  .90  1.21  14.6  91  TABLE VII PURE HELIUM Initial Pressure  Pressure Increase  Cm.  Mm. Hg.  Cm. H2SO4  Mm. Hg.  %  11.90  16.06  .46  .62  4.34  18.80  25.38  .58  .78  3.62  30.66  41.39  .90  1.21  2.89  LEGEND Hydrogen presaure  L T  3 '34 tmn 11  98 -  O 19 - 8  1  "  o d 3? 7 7 08 " curves-in x m m . o^Hgf. * 62 7 0 -various  Pressure  oi* Helium  ttt tttw. Hg.  PART  II  THE ADSORPTION OF HYDROGEN BY SULPHUR  TABLE OF CONTENTS  Page. Introduction  1.  Apparatus  2.  Diagram of Apparatus  (to face) 2.  Experimental  3.  Purification of Sulphur  4.  Results using Liquid Air  6.  Discussion of Results  7.  Summary  8.  THE ADSORPTION OF HYDROGEN BY SULPHUR.  Introduction. The theory that solids are covered with a layer of adsorbed gases is now commonly accepted. in various papers  Irvine Langmuir  has shown that this layer is most  probably only one molecule in thickness, and, from the great difficulty he found in removing the adsorbed layer he concludes that the gas molecules are held by the solid in a state of semi-chemical combination with the unsaturated valences of the outer molecules. With the object of confirming the theory of adadsorption, it was proposed to prepare a gas free surface and determine whether a gas would adsorb on the surface as it was formed.  In view of the difficulty found bv Langmuir in re-  moving gases once they were adsorbed it was decided that the most satisfactory method of preparing this surface woulg be to crush a solid into a powder.  The solid chosen was sulphur,  as it could be easily crushed to a fine po?/<3er, thereby providing a large amount of fresh surface.  Hydrogen was  selected as the gas to be adsorbed, as it was known to have a 1.  Am. Chem. Soc. 40 I36I (l?l8) Trans. Faraday So*c. 17 Part III (l?21) Phy. Rev. K I65 (1?16)  strong affinity for sulphur and therefore would be more likely to adsorb. Apparatus. The apparatus used for crushing the sulphur consisted of a Pyrex glass tube (A) about 1 inch in diameter, inside of which v/as a bob of iron (C) which fitted closely to the tube.  Into this bob was screwed a rod of iron 1.3 inch  in diameter and 7 inches long.  The tube A was sealed to a  smaller tube (B). .Closely fitting about B v/as an electromagnet made of a solenoid of about 500 turns of copper wire. The apparatus was arranged so that when the crusher rested on the bottom of A about 2 inches of the iron rod extended into the magnet.  The solenoid was connected to 12 volt D.C. with  an electric metronome to make and break the circuit.  As the  current went on and off the crusher was raised ang dropped, crushing the sulphur (F) at the bottom of A.  By this method  a gram of sulphur could be reduced to a fine powder in a few hours. The hydrogen was prepared by the electrolysis of a saturated barium hydroxide solution and dried by calcium chloride and phosphorus pentoxide. The sulphur was purified by fractional crystallization of roll sulphur. cool,  1400 grams were melted and allowed to  '.'/hen about half the sulphur had crystallized the re-  mainder of the liquid was poured off.  The crystallization  was repeated twice and the final fraction v/as kepi over  calcium chloride.  This sulphur was used for all the work  described in this paper. Experimental. From 1-1.^ gM* sulphur were weighed and placed in the tube A, in which the crusher had already been placed.  The  bottom of the tube was sealed off and the apparatus connected to the small tube G leading to the McLeod gauge and the mercury diffusion pump..  The apparatus was then pumped out to a com-  plete vacuum and the stopcock connecting the diffusion pump was turned off.  Hydrogen was then admitted to a pressure of  -3 the order of 10 ^ mm. of mercury and the crusher started. Pressure readings were taken at intervals of about five minutes. Instead of dropping, as was expected, the pressure increased steadily as the crushing went on.  In order to  determine the cause of this pressure increase a fresh sample of sulphur was crushed without any hydrogen present.  It was  found that the pressure increased exactly as before.  If the  sulphur was allowed to stand in the evacuated bulb without crushing no increase in pressure was noted.  These facts in-  dicate the gas was evolved by the sulphur and, since it was only evolved on crushing, that it must be held in a very tenacious manner.  A series  of readings, typical of the  pressure increase due to the gas given off by the sulphur is given.  Time miii.  Pressure  0  22  4 18 23 4?  35 45 65  62 72 88  3 9  28  60  83  93  133  122  135  * 140  Purification of Sulphur. Attempts .were made to free the sulphur from the gas by the following methods. 1.  Vacuum Distillation. About 3 gm. of the recrystallized sulphur were  distilled in a vacuum, using the apparatus shown in Fig. 2. The sulphur was placed in one arm and the apparatus pumped out.  The stopcock was turned off to prevent any sulphur into  getting into the pump, arm.  and the sulphur distilled/the other  The apparatus was again pumped out and the sulphur dis-  tilled back.  This was repeated three times.  The sulphur was  removed and kept over calcium chloride as before. 2.  Crystallization from Carbon Disulphide. On the possibility that gas was more soluble in  carbon disulphide than in sulphur, some of the sulphur was disolved in carbon disulphide and allowed to crystalUze out. This was repeated several times and the sulphur was then fused and kept in  a molten state for some tine to drive off  any traces of carbon disulphide.  3.  Crashing and. Fusing. About 2 gm. of the sulphur were placed in the  crushing apparatus and crushed, at the same time pumping off the liberated gas.  After some time the pump was disconnected  and a few minutes later the pressure was measured.  If there  was no increase in pressure the pump was connected again and the crushing continued till on repeating the procedure no increase in pressure was noted.The sulphur was then fused in the bulb. 4.  Fusing in Crushing Bulb. From 1-1.3 gins, sulphur was placed in the bulb  and the crusher held up by means of the electromagnet.  The  sulphur was kept in a molten state for 10-13 minutes, the apparatus being pumped out at the same time. then allowed to solidify.  The sulphur was  This method was very unsatisfactory  as, owing to the low pressure, the sulphur sublimed before it melted and was distributed over the walls of the tube. In the last two methods described it was noticed that the sulphur blackened when in the liquid state.  This  ascribed to traces of mercuric sulphide formed by the action of mercury vapor from the manometer. The four methods of purification may be discussed together.  In all cases the treatment had no effect, since  the evolution of gas was the  same after treatment as before.  Even after the third method, when the sulphur was crushed and fused, it was found that the rate of gas evolution was the  same as before. Results using Liquid. Air. In order to obtain some information as to the nature of the gas and. as to the action of the hydrogen, a liquid air trap was placed between the crushing chamber and the manometer. This also had the effect of condensing any mercury vapor from the manometer. Sulphur was crushed without any hydrogen being present and it was found that, when the liquid air was around the trap, the pressure remained constant.  After crushing for  some time the liquid air was removed and the pressure immediately increased showing that the gas had been evolved as before but had been condensed by the liquid air. The experiment was repeated with fresh sulphur in the presence of hydrogen.  On allowing the sulphur and hydrogen  to stand without crushing, it was noted that there was a slow decrease in pressure for about five minutes after admitting the hydrogen.  After this pressure drop had ceased, liquid air  was placed around the trap and the sulphur crushed as before. As long as the liquid air was around the trap the pressure gradually dropped.  'Then the liquid air was removed the pressure  immediately increased to a value corresponding to that found when no liquid air was used.  On replacing the liquid air the  pressure dropped again to the value obtained before Its removal . A series of readings for Ihe pres3"re 'vben using  7 liquid, air is given below. Min.  Reading  0  23 liquid air off bulb  3  20 started crushing, liquid air around trap.  4  1?  6  IP  7.5  18.3  8.3  18  27  17.3  37-3  17  Discussion of Results. 1.  The Nature of the Gas Evolved. The following facts are to be noted regarding  the gas.  It is in a stete of very close combination with the  sulphur as is shown by the great difficulty found in removing it and by the fact that it is only given off when the sulphur is fused.  It is condensible in liquid air.  This combined  with the fact that hydrogen sulphide was given off during the purification by crystallization leads to the conclusion that the gas in hydrogen sulphide.  It is possible that the hydrogen  sulphide is in a state of combination with the sulphur similar to that of the polysulphides of the alkalies. 2.  Action of the Hydrogen with the Sulphur. It is apparent that there is some action be-  tween the hydrogen and the sulphur.  As was previously men-  tioned, it is impossible to say conclusively, from the data  advailable, whether the hydrogen adsorbs on the sulphur or reacts with it to form hydrogen sulphide.  The initial drop  in pressure when the hydrogen is first admitted to the reaction chamber indicates that the reaction is adsorption rather than chemical combination.  It is obvious that if the hydrogen re-  acted with the sulphur to form hydrogen sulphide there would be no pressure drop since the hydrogen sulphide formed would replace the hydrogen sulphide used in the reaction. Summary. 1.  Ordinary roll sulphur contains large quantities  of hydrogen sulphide, which cannot be removed by ordinary methods of purification. 2. atures.  Hydrogen acts upon sulphur at ordinary temper-  Experiments described indicate that  adsorption rather than chemical combination.  the action is  


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