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The diffusion of gases of the atmosphere through hot quartz Harris, Joseph Allen 1923

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Qj«tfrtJ^ S O U . • p * t ^ '  _TKE DIFFUSION OF GASES OF THE ATMOSPHERE THROUGH HOT QUARTZ, by Joseph Allen Harris  A Thesis submitted for the Degree of MASTER OF ARTS in the Department of CHEMISTRY.  THE UlTIVERSITY OF BRITISH COLUMBIA. APRIL  1925  Stable of Contents T  Historical'.  TT Object of the Research, 111, Apparatus, IY  Prooeedure• [b*l Method of analysis of the gases, (a) Rates of Diffusion.  J  Calibration of Apparatus, (a) The Resistance thermometer. (b) The Volume of the apparatus, (o) Volume of the quartz bulb. (d) Calibration of McLeod gauge. (e) Area and average thickness of the quartz.  Y£  Calculation of Results.  VII.  Experimental Results. (a) Analysis, (b) Diffusion Rates,  VIII. Discussion of Results.  IX.  Summary. Bibliography.  (I)  The Diffusion of the Gases of the Atmosphere through Quartz HISTORICAL; While endeavouring to evacuate a sample of prepared cocoanut charcoal, contained in a quartz bulb at temperatures in the neighborhood of 950 0, it was found by the writer that it was impossible to maintain a vacuum at these temperatures.  Three sugestions as to the cause , presented  themselves. (1) The presence of a minute leak in the appar- atus (2) Action of the silica O Q the carbon at high temperatures. (3) Diffusion of gases of the atmosphere through the quartz. On allowing the quartz bulb to attain room temperature and again evaouating, it was found that no increase in pressure occurred,thus dispelling the idea of leakage. The quartz bulb was now removed from the apparatus and the charcoal extracted. On examination of the walls of the bulb there was unmistakeable evidence of interaction of the silica on the charooal. There was still the possibility of  .  diffusion taking place also; so accordingly , the bulb was oarefully cleaned, dried and replaced in the apparatus. The whole was again carefully evaouated and allowed to stand overnight at room temperature. The following morning there was no sign of any diffusion having taken place at this temperature. The temperature of the bulb was now gradually raised to the original working temperature, and immediate signs of diffusion were noticed. It was decided to make a study of this.  (2) Previous workers in this field. That quartz is permeable to gases has "been shown "by previous investigators. Villard (l) worked with hydrogen, and found that at temperatures in the neighborhood of 1000°C., diffusion proceeded quite rapidly. Johnson and Burt (2) have noted the diffusion rate of hydrogen through quartz, and also state that Eitrogen may diffuse in the neighborhood of 600 C. Jaoquerod and Perrot (3) shcjpd similar properties for helium. Richardson and Ditto (4) attempted to detect the presence of the heavier inert gases, ( Xenon, Krypton, Argon anf leon) in minerals . Their observations showed that neon possibly diffused through red hot quartz tubes, but no evidence of argon diffusing could be detected. Mayer (5) conducted a series of experiments on the leakage of hydrogen, nitrogen and oxygen through a quartz tube, and attempted to determine the relation between the amount of leakage and the pressure and temperature of the gas. His work appears to be the only previous study of the diffusion of oxygen through quartz. In the case of oxygen and nitrogen he stated that no leakage oould be detected for pressures of less than one atmosphere. Under approximately like conditions he found that hydrogen leaks the most rapidly, and nitrogen the least rapidly.  (3) Object of the present Research: In this case the object was to make a study of the nature of the gases that were diffusing, their rates of diffusion at atmospheric pressure, and the influence of temperature on the diffusion rate.  APPARATUS: A diagram of the apparatus is given on Plate I. The bulb B, was of transparent quartz , and was connected to the apparatus by means of a carefully ground joint A.  Heating was effected by means of an electric fur-  ness , platinum ribbon being used in its construction. This was controlled by means of a large rheostat, and the temperature read by means of a platinum resistance thermometer* The thermometer was calibrated against ice, stem and sulphur vapour, according to the method as outlined by Robinson ^merioan Inst. Mining and Metallurgical Sngin. 1920 , p.450] The calibration curve was drawn according to the equation R  t *  R  o( I + at + B t2) so as to give accurate readings to  one degree centigrade. ( Graph I) Mercury sealed stopcocks H and I allowed the bulb to be isolated from the apparatus at any time, while between them, connection oould be made to a manometer when desired. The volume of the apparatus was obtained by means of a Toplerpump T, The large McLeod gauge FG was used in the analysis of the gases. Both of these  (4) could be disconnected from the rest of the apparatus by means of the cook J,  Pressures were read  on the smaller  McLeod Gauge OR,readings being possible to !<)""* num. The apparatus was connected by a stop-cock L, to two mercury diffusion pumps P, whioh in turn were connected to a water pump at V. By means of these pumps evacuation of the apparatus was possible in a few minutes. X is a hydrogen generator, entered on the diagram but not used during this research, since air was used in the calibration of the volume of the apparatus. Drying tubes atX removed any moisture from the air used during the calibration.  0—  0  PROCBBDURE The a p p a r a t u s was c a r e f u l l y t e s t e d for any p o s s i b l e l e a k by e v a o u a t i n g , c l o s i n g the cook a t L, and allowing to s t a n d o v e r n i g h t . The temperature of the furnace was now r a i s e d to working temperature and the whole of t h e apparatus again c a r e f u l l y evacuated. As soon as t h e furnace had assumed a oonstant t e m p e r a t u r e , and the McLeod gauge showed no p r e s s u r e , t h e cocks a t J and L were c l o s e d , and the time n o t e d . The p r e s s u r e s read were t h e n p l o t t e d a g a i n s t the t i m e , c o r r e c t i o n s over the whole volume having been made for v a r i a t i o n in room t e m p e r a t u r e . [ G r a p h # 3 ^ Prom these curves t h e p r e s s u r e r a t e s a t d i f f e r e n t  temper-  (5) atures, in millimeters press, per second were obtained. The rates of diffusion in cc/seo., through quartz of area .o#e square centimeter, and thickness one centimeter were then calculated and plotted against the temperature.  Method used in the Analysis of the Diffused Gases. Even after continuous runs of 150 hours and temperatures in the neighbourhood of 1000 0. the small amounts of the gases present made it impossible to use ordinary methods of gas analysis. Richardson (4) showed that hot calcium absorbs all of the chemically active gases except Hydrogen. Sievertx (6) has shown that while some specimens of commercial Calcium unite with Nitrogen, only above 800°C, the majority of them exhibit a second zone tff activity between 300°C and 500°C, with an optimum at about 440°9. Soddy (7) has also shown that, provided the initial pressure does not exceed a few millimeters, all the msmms. o  common gases are completely absorbed between 700°C and 800C by Galcium. Moreover he found this metal to be of great value in the separation of the rare gases of the atmosphere, Thus since no absorb&ion by Calcium takes place below 300*C it was decided to use this metal as the absorbent for Nitrogen, and to use 6-opper for the determination of any Oxygen that might be present. As mentioned above, on acoount of the small amounts of gas present , it was necess-  (6) ary to devise a special means of analysis. Consequently a large MoLeod gauge was constructed (see Plate TT ) The scale G was 50 cm. in length thus allowing a wide range of readings. Instead of having the usual closed capillary, a short capillary tube was sealed into the bulb F at S. This was then bent at right angles and drawn out at the end. This was now  fastened into a small quartz tube, 10 cm. long  which contained the absorbents. The copper used was granular, being freshly reduced from the oxide by means of a current of hydrogen. This was contained in the tip of the tube at M. A layer of broten quartz separated the copper from finely divided metallic Calcium, which in turn was separated from the joint D also by pieces of quartz. The mercury in the gauge was brought up to the level U, and held constant in that position. The joint D was now carefully covered with moist filter paper, and the quartz tube heated to redness as a test for any adsorbed gases. Having made certain of the entire absence of any gases the mercury was withdrawn, and the guage again evacuated. This was accomplished by closing the colts H and K, opening J and connecting to the pumps. In this way only the diffused gases contained in the connecting tubes were lost, the bulk being present in the bulb B, and the Mc Leod Gauge OR. (Plate I). The cooks were  —^—  PLq-rt u  (7) then reopened, and the gas drawn into the "bulb of the gauge Fj the mercury was then raised again to U, and the pressure-read on the scale G. The quartz tube was now covered with moist filterpaper with the exception of the tip containing the oxygen absorbent. This was then heated to redness,, a sudden drop in the pressure denoting the absorption of the oxygen. The quartz was then allowed to cool , the mercury lowered in the bulb in order to thoroughly mix the remaining gases,and then brought back to U. The copper was again heated and the above process repeated until a oonstant pressure was obtained. The tube wa& again allowed to oool", the filter paper covering the calcium moved to oover the cement at the joint D» and the whole tube reheated. A sudden drop showed that the Nitrogen present was being absorbed. The proceedure was repeated as in the case of the oxygen until a constant pressure was again reached. Any residual pressure would indicate the presence of rare gases, since they are not affected by the above absorbents. A sample of air subjected to this method of analysis gave ready indication of their presence. Prom the relative pressures, the relative amount of oxygen and nitrogen may be calculated.  Owing to the  extremely low rate of diffusion at low temperatures it was only possible to obtain sufficient gas for analysis at the higher temperatures.  (I)  (a)  yumuw fala wu oallaratod afalaat aoltlaf loo, atom, aaA aalpaar vapoax. fho oallaratloa oarvo woo Araam aoooHtla* to taa oqaatloa; 1* » lg( I • at • It*), wharo Ro la taa roalat~ •4 taa aaltla* polat of laa, l v taa roalat* at aai taayorataro t , ahilo a, aai 1 ara oonatanta. OalaalataA from aaoro w oataia taa valaaa.  a - .009468.  B • -0000004194.  faa aallaratloa oorro ( Oraph X ) waa dram aaaarilag to tao valaaa aolov , oa a aoalo that 9ava aaaarata roailnfa to 1*0• loo la t tao t (oaa»)  faasaratara 0.0 100. 0 900.0 900.0 400.0 900.0 900.0 TXO.O 990.0 990.0 990.0 990.0 900.0 910.0 990.0 990.0  at.tt •9.01 99.99 106.40 X99.9? 199.94 166.96 191.91 199.91 199.99 191.99 194.1V 194.69 199.09 199.94 199.90  IKtfff  -  tE&sS  ....  0.  (9( Calibration of Resistance Thermometer (oontd)  Temperature  Resistance 198.44 199.85 201.23 203.93 206.69 208.07 209.40 210.74 212.09 212.75 213.42 214.76 216.05  890.0 . 900.0 910.0 930.0 950.0 960.0 970.0 980.0 990.0 995.0 1000. 0 1010. 0 1020. 0  (b) VOLUME OF THE APPARATUS. Air was drawn into the apparatus through the drying tubes X ( Plate 1 ), and the pressure read on the manometer HI. The air was then pumped out by means of a Topler pump and collected in a eudiometer toy displacement of mercury. The eudiometer had been calibrated in the usual manner, by weighing with distilled water. A calibration curve was drawn (Braph 2) to a scale reading correctly to .01 cc. Three determinations of the volume of the a-ptmratus were made. These gave values of ;(a) 217.6 ; (b) 217.3 ; (o) 217.25, from which the value of 217.3 was taken as average. Calibration of Eudiometer, [Graph 2]was drawn in accordance results. (Scale Read.  Wt water{21.3 CJ  2.0 6.8 18.0 29.0 39.0 50*0  148.35 153.10 164.25 175.22 185.17 196.06  Volume oo 148.646 153.406 164.578 175.704 185.540 196.452.  S3 r a - t 3 ^ "  BSH  ?#  ;  C o cr M  Jo  tu tt  (J  \o  6-  140  ISO  Ibo  170  i«o  1^0  -5.0O  a.o  V O L U M E IN C.C .  ff CflLlBR.RTIOrt O F EluOIOMETER.  (10) (o) Volume of the Quartz Bulb. Since the gas contained in the quartz bulb was at the temperature of the furnace, while the r e s t of the apparatus was at room temperature, the volume of that part of the eulb extending into the furnace had to be determined in order to make c o r r e c t i o n s . The volume was determined by weighing the bulb cont a i n i n g d i s t i l l e d water, and gave a value of 59.17 oo. (d) Calibration of the MpLeod Gauge: This was calibrated in the usual manner by filling with mercury and weighing. The total volume was found to be  47.3991 oo , while the  oapillary had a volume of .0013673 oo per mm. length. Three points of reference ojj the scale were ohosen such that when the mercury level was brought to these points, each mm. difference in level was equivalent to 1 x 10*4 mm. pressure at the upper level, 1 x 10"* at the intermediate level, and 2 x 10-3 mm. at the lower one. (e) Area and average thickness of the Quartz bulb. The weight of the portion of the quartz tube projecting into the furnace was obtain-  (11) ed, and assuming that fused quartz has a density of 2.65, the total volume of quartz was calculated and found to he 18.628 cc. As the bulb and connecting tube were fairly symmetrical, the superficial area could be easilly determined by obtainthe outside dimension of the bulb. This area was found to be 120.07 sq. cm.  The thickness was  then determined approximately by finding the ratio  of  volume to area . Prom this uiiickness, the  inside area oi «he bulb was calculated, and the effective area calculated by taking the mean value of the two above areas. This area was found to be 112,12 sq. *m.  By dividing the volume once  more by this area, the true thickness was found to be 18.688/ 112.12 or .166 cm. CALCULATION OP RESULTS •  The number of oc. of gas at I« T.P diffusing through 1 sq. cm. of surface, and a thickness of 1 cm. under actual partial pressures existing in the atmosphere, at any constant furnace temperature, will be taken as our unit. The pressures read off were corrected for room temperature, and plotted against the time * ( Graph #3) The average slope of these curves gave the ratio of increase in pressure in mm. per sec.  (12) These rates were reduced to co. per seo. in the following manner. Let p he the pressure rate in mm per sec. pg - 760 mm. v'' = volume of the apparatus at furnace temp. vK = volume of the apparatus at room temp. T 0 = 273 tf s furnace temperature in deg. C. t r = average room temperature " ". T = 273 + tf-tr Y 0 • total volume at H.T.P. in co. per seo. v0'', and VQ are the volumes of the apparatus at furnace temp, and room temp, respectively, under H.T.P. Then ? 0  - V x p/po x T0/T0f  Since this part of the apparatus had been corrected for room temperature this equation becomes, vo  =  v' x p/p0  Since the second volume had been corrected for room temperature but not for furnace temperature we have, v£  *  v*' x p/p0 x T0/T  Therefor Po( ^ - £ ( 158.2 + 59.17 x 273 ) 760 tf-tr+7TJ  The rate V 0 is also a function of the area, and of the thickness of the quartz. It has been shown for other cases of diffusion, that the diffusion rate is directly proportional to the area and inversely to the thickness. If K is a constant, A , the area in sq. cm. and 1 the thickness of the quartz bulb, Y0  3  K x A/1  , or K  -  Yn x 1 A  (13) Then K is the number of co. of gas at 1T.T.P. diffusing through 1 sq. cm. of quartz of 1 cm, thickness, per second. -o-o-o-o-o-o-o-o-o-o-o-o-o-o-oBZPERIMBNTAL RESULTS. The analysis of the gases that had diffused at temperatures of approximately 1000 0 is given below. Init Press.  After Cu.  lafter Ca.  8.5 7.5 8.2 8.6  0.0 0.0. 4.0 0.0  39.0 35.3 51.4  £~0T 81.1 80,8 81.11 85.66  T^F 18.9 19.2 18.99 14.34  Th$ ladt analysis was for a lower temperature, Diffusion i^ates. The pressures and times of run, from which the pressure rate ( Graph 3) is calculated was drawn according to the values below . /Time in mins. Temp. 1017 C.  Temp 995 C  Temp 967 C,  45 60 90  Press. . cm x 10" 4  Press. cm. x 10~4|  Time min.  9,027 10.782 17.35  30 50 75  6.669 10.280 14.1924  fe  35 66 84 97 126 143 163  4.2722 8.1033 10.9600 12.3414 15.1855 18.3975 19.9290  30 75 JL35 190 240  3.2964 9.8990 15.5740 20.7834 26.8375  120 150 180 210  9.975 , 12.2850 I 14*8575 16,8800  60 80 210  4.9350 6.8145 17.6400  (14) Temp.C. (1) 918'C  Pressure . om x 10  Time in mins.  30 60 150 210 270  1.9657 4.05212 10.6719 14.8845 19.4982  893"0  30 60 100 120 180 195  1.3065 3.5790 6.5425 7.8088 10.3515. 11.8590  800'C  20 30 80 120 150 180 220 240  1.6783 2.5426 3.7888 5.9094 7.7284 8.4822 10.8075 11.8065  15 75 100 120 160 210  .5460 3.4755 2.6103 4.4310 4.5500 6.0790  15 30 45 75 90  .1995 .3255 .5460 .9870 1.2390  775°C  749 °C  press.in om x 10"*  Time in mins.  2  50 60 90 150 165  £.0900 5.2651 6.4018 9.0550 10.5726  •  135 180 210 240 270 390  1.47 2.52 3.013 3.335 3.9580 5.635  Ho d i f f u s i o n was obtained below tempe r a t u r e of 720*C  GRAPH m  (14 a)  By taking the average slope of these diffusion ourves, ( graph 3) the pressure rate in mm. per second was obtained oner the different temperatures. Substituting in the equations on page 12, the volume rate is obtained in cc. per second. From these values the unit of diffusion K can be calculated.  Vol. rate  press rate  Temp room.  Temp furn.  *r  tf  18  749  .2381 x 10" 6 ,  n  775  .4660  N  800  ll  K  vc  P  .5447 x 10-7  .8066 x 1)  1.067  1.580  .8000  1.8264  2.7046  893  1.0400  2.3574  3.4910  tt  918  1.2000  "  2.7154  4.0210 •  n  967  1.3640  "  3.0789  4.5594  tt  995  2.0330  "  4.5790  6.7810 "  it  1017  3.1660  8.6256  12. 6220 "  "  " ,T  n  (15) DISCUSSION OF RESULTS It is evident from the above analysis that the major part of the observed diffusion is due to the passage of oxygen through the quartz. Furthermore, contrary to expectations, atmospheric argon takes no perceptible part in the diffusion. It is impossible on the basis of the present results to calculate the individual diffusion rates of oxygen and nitrogen, as it is by no means certain that the rate will be directly proportional to the external pressure. If, however we assume for the moment that it is proportional to the pressure, then it can be seen that the diffusion rate of oxygen is 80/20 x 4/l or sixteen times that of nitrogen, under equal external pressures. While, as pointed out above, this value cannot be relied upon, it does at least indicate that the diffusion rate of oxygen is many times that of nitrogen. The results indicate that there is also a possibility that of the gas diffusing at lower temperatures scsKxi more oxygen would be present, thus indicating an even higher ratio at these temperatures.["Graph 4]indicates that the diffusion rate increases with temperature, at first as an almost linear function, and later at a much higher rate SJwo points lie somewhat off the curve, otherwise quite a smooth curve is obtained. Furthermore, extrapolation of the curve would indicate no diffusion at 705°C. One observation was made at 720* C for 11/2  hrs. which indicated no  (16) diffusion at this temperature. It has not since been possible to verify this minimum temperature, as the elect-ric furnace burned out at this point, and is now being repaired. On the whole,therefor the curve gives a fairly reliable indication of the variation of diffusion rate with temperature. This is the first known investigation of the identity of the atmospheric gases diffusing through hot quartz. The diffusion of argon through hot quartz as investigated by Richardson and Ditto (4) is still in doubt though no evidence of diffusion was noticed in this case. The diffusion of oxygen and nitrogen have been investigated by Mayer (5), who used the almost unworkable method of measuring the decrease in pressure inside the quartz bulb caused by diffusion through the bulb to the outside. He stated that no diffusion of oxygen or nitrogen was obtained below one atmosphere pressure, which is directly contradicted by the present results. Furthermore,he operated at a maximum temperature of 3J80 C, and a minimum of 280.9. This is below the range at which diffusion would occur according to the present results. As Mayer reports only a few small graphs , which are absolutely unaoompan-ied by data of any kind» his reference cannot be taken seriously. Since the completion of this thesis, a reference to the work of Johnson and Burt (2) on the diffusion of nitrogen from the air has appeared in the current number  (17) of Chemical Abstracts. The original article is not available at the present time, and information in the abstract is rather vague. However, it appears that Johnson and Burt obtain an initial diffusion of nitrogen at 600*0, which is more in accordance with our results. Furthermore it is stated that the diffusion of nitrogen increases very rapidly with temperature, and the abstract gives the impression that all of the diffusion is ascribed to the I£. SUMMARY. The results of this research may be summed up as follows. (1) Hot quartz is permeable to the atmosphere. (2) Analysis of the gas obtained by diffusion gave about 81$ Og, 19% Eg and no perceptible amount of argon, thus showing that the rate of diffusion of oxygen is many times that of of nitrogen. (3) The diffusion rate increases at first linearly, and then more rapidly with the temperature. Extrapolation indicates zero diffusion at about 700 C. In conclusion the writer wishes to express his appreciation of the help and assistance given by Dr. M.J. Marshall, under whose direction this work was carried, eat  especially in the construction of the apparatus with«-  out whioh this thesis would have been impossible, Chemical Laboratories, University of British Columbia.  Bibliography* (1)  P . V i l l a r d , Gomptes Eendus. 1900, v o l , 130, p 1752.  (2)  Johnson and B u r t ,  J o u r n . O p t i c a l Soo. Am. 6_ , 734-8, 1922.  (3) Jaoquerod and Perrot, Archives des Sciences. 1904, vol. 18, p. 613; volEO p454. (4) Richardson and Ditto. Phil. Mag. 22 704-6. C.A. 6_ . 1392. (5) Mayer, C.A. 10, 140. Phys Rev. 6, (1915) 288-91, 66)  Sievertz. Journ. Soo. Chem. Ind. 35, (1916) 119-20 Z.Elektrochem. 22, (1916) 15-8 Chem. Zeit.  28  (1915) 619-20  Z. Angew. Chem. 39 (1915) 804. (7) Soddy,  Bature 79_, 129, Phil. Mag. 16, 632. Chem. Hews, 94(1906) 305, Chem. Hews  95( p, 13, 25 , 45, 61,)  Proc. Roy. Soo. 78. 429- 58.  


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