A SPECTROSCOPIC INVESTIGATION OF RETRO GRADE RAYS IN HELIUM BY WILLIAM JACOB JENSEN A.B. Carleton College, 1920 THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS IN PHYSICS IN THE GRADUATE SCHOOL OF THE UNIVERSITY OF ILLINOIS, 1922 URBANA, ILLINOIS . .. 1 9 UNIVERSITY OF ILLINOIS THE GRADUATE SCHOOL Jung i HEREBY RECOMMEND THAT THE THESIS PREPARED UNDER MY SUPERVISION BY WTT.T.T ftM JAC OB JEN SEN ENTITLED RAYS Pi R^t.tum _ BE ACCEPTED AS FULFILLING THIS PART OF THE REQUIREMENTS FOR Recommendation concurred in* Committee on Final Examination* ^Required for doctor’s degree but not for master’s Digitized by the Internet Archive in 2015 https://archive.org/details/spectroscopicinvOOjens TABLE OF COD TENTS I. INTRODUCTION A. Purpose of the Investigation, . . . B. Historical Review . , II. PRODUCTION OF RETF . ill. THE APPARATUS A. T Discharge Tube Proper ...... B. The Exhaus C. The Cathode and the Anodes D. The Priming System u. The Spectroscope IV. MANIPULATION A. Mounting the Tube B. Procedure for Priming C. Qg the Observations V. DATA A. Observations B. Table for Comparison VI. CONCLUSIONS 1 1 4 4 5 3 6 6 7 7 8 9 11 12 I. INTRODUCTION A. Purpose of the Investigation .- The purpose of this investi- gation was, primarily, to study spectroscopically the retrograde rays obtained in a discharge tube when helium is the residual gas, and to compare the same with a similar study of the positive rays formed in the same tube. To this end Special positive ray tubes containing hollow cathodes were constructed. Incidental to this study several other factors presented themselves which, if time per- mitted, were to be investigated, such as the origin of the retro- # grade rays, whether they are present when the canal through the cathode is closed, the effect of the shape of the vacuum tube upon the presence cf the retrograde rays, and any other factors that in any way affect the production of retrograde rays; and, conversely, the effect cf the retrogr3.de rays themselves upon the glass and metal parts of the discharge tube. E. Hist or i c al R e v i ew . - Positive or canal rays were discovered by Goldstein in 1SS6. They have their origin in front < e cath- j ode in the edge cf the Crookes dark space, fall towards the cathode ! under the action of the electric field, and attain a high velocity. I If openings are made through the cathode, the canal rays stream through the openings, or canals, and appear on the other side as distinct rays or beams. Because of these openings, or canals, through the cathode, Goldstein called the beam streaming through "canal rays”, although they are now commonly called positive rays. The color of the canal ray depends upon the residual gas,- and is generally different in color from the cathode ray for the same gas.' Goldstein also observed that there was a faint additional beam, having the same direction as the cathode beam, that seemed to be a continual; ion of the positive ray, though in the opposite direction. For this reason he called the rays composing this beam "retrograde . .... s". Subsequent investigations have -shown t . retrograd rays consist chiefly of positive ions, molecular in size, though the rays may also contain negative ions, or indeed neutral particles, atomic in size. That four types of particles are present in the beam leav- ing the cathode — cathode rays (electrons), positive particles atomic in size, and neutral atoms — is evidenced by the accompany- ing photograph taken by Professor Uni: 13. (Photograph Hc..l) . The exposure was made in front c? the cathode, and shews the mag- netic and electro-static deflections of the charged carriers, and the undeflected central spot due to the neutral particles atomic in size. Villard* obtained the spectrum of hydrogen and oxygen for retro- grade rays in residual air, and showed by the magnetic and electro- static deflections that the ray was made up chiefly cf positively charged particles much heavier than the negative particles of the cathode beam. rr> J.J. Thomson measured the magnetic and electrostatic deflec- tions on a phosphorescent screen, and cu.. e to the same conclusion as Villard. He further showed that the intensity of the phosphores- cence due to negatively charged particles was much greater than that due to positively charged particles for retrograde rays, while the opposite was true for the ordinary positive or canal rays. The difference in the phosphorescence cf lithium chloride when * P. Villard. C . - H endue, 143; pp 374—876, Nov. 5,1806. 3 J.J. Thomson. Phil. lag. XIV, p 353, 1907. . . • I '■ • . ' " 3 struck by positive rays and when struck by cathode rays affords a simple way of investigating the path of the retrograde rays, and the origin of the canal rays. Lithium chloride phosphoresces a rich deep red when positive rays impinge upon it, and it gives the bright red line of lithium in the. spectrum. Cathode rays cause a steely blue phosphorescence which gives a continuous spectrum. By means of a small mica screen coated with lithium chloride, different regions of the tube can thus be investigated. O.H. Smith 3 investigated the retrograde rays from a cold cath- ode, measuring t efle ns by . eans of the t .. on a photo- graphic plate. He found that for retrograde rays in residual air the hydrogen molecule appeared on every plate, accompanied by a heavier carrier which in most cases was the oxygen molecule; that the negative lines were sharper and clearer than the positive lines — probably because of the disturbance of the path of the positive ion in becoming positive; that retrograde rays could be produced with a cathode having a bore in the canal as small as .05 mm. in diameter; that the best range of pressures was from .008 to .015 mm. of mercury; and finally, that the power of a moving particle to af- fect a photographic plate seemed to be a function of its kinetic energy. The mere sensitive methods that have recently been developed for the investigation of positive rays might well be applied. in the investigation of retrograde rays. * J.J. Thomson, Rays of Positive Electricity. 2 O.H. Smith, Phys. Review, 7, pp 635-633, June 1916. . . . . . . . . . 4 II. METHODS OF PRODUCING RETROGRADE RAYS The type cf cathode used determines, to a -great extent, the in- tensity of the beam produced; sc does also the shape of the discharg tube. A double cathode made cf t . _ . ..dial triangular plates, or one made of a wire gauze, give rich sources of retrograde rays — though in any case they are weak in comparison with the canal rays. A hollow cylindrical cathode, having the ends closed with discs Which have - all central apertures or slits, gives a rich source of positive rays, and also of retrograde rays. The shape cf the discharge tube, due to the electrostatic in- fluence cf the walls, is a deciding factor in the definition or con- centration cf the beam produced. III. THE APPARATUS A, The Di sc harge Tube Proper .- The tube was made of pyres glaa and was the so-called "dumb-bell” type developed by ICnipp and Kunz, It consisted essentially of two bulbs, made .from 1.5 liter flasks, joined together by a tuoe in the center cf which was a hollow, cylindrical cathode, K, (Plate I). The outer tube, T^, joining the two bulbs and Ag, was 36 cms. long by 4.3 cms. diameter. The inner tube. To, was sealed in by the ring seal, S, and was ex- actly concentric with the outer tube. This inner tube was 10 cms. long by 3 cms. in diameter, and was drawn in at n so that the cath- ode was held concentric within the tube. The purpose of this in tube was to get the face of the cathode nearly flush with the walls of the neck cf the tube, which has been shewn to be the best condi- tion for a concentrated beam (J.J. Thomson,— Rays of Positive Elec- tricity). The large ground joint, Jg, permitted the removal cf b 5 bulb A p, thereby givii ?o ess to the cathode. By removing cat hods . inal plug fro,: the ground joint, J„, and unscr vi ig the stem from the cathode, the cathode could be removed and be replaced by another — or any other changes made. The stem which held the cathode in place as enclosed by a small glass tube, as may be seen in the diagram. An anode was sealed into each bulb hy means of tungsten seals through special intermediate ^lass so that the retro- grade rays could be formed in either side cf the tube at will. was a charcoal bulb for removing all absorbable gasses. The small tube, P]_, for priming, and the stop cook, Q.p, for shutting the tube off from the exhaust system, are shown in Plate II. E. The Exhaust Line and Pumping System .- The connection of the tube proper through the exhaust line to the pumping system is shown by Plate II. This unit .-.as connected t ground point, J3. Q P was a stop cock for shutting off the pumps from the rest of the system while the tube was beii primed. The liquid air trap, B3, prevented any mercury vapor from entering the system from the pump. The phosphorous pent oxide bulb, B^., removed all ... - the system, while the chare , •W moved all absorbable gasses during the process of priming the tube. Pg was a capillary stem for letting down the vacuum in the system. C. The C . . _ai tne Anodes .- The cathode was made entirely of aluminum, being the hollow, cylindrical type. Plate III shows ■ - construction. The drawing represents the cathode twice actual size in order to show the construction more clearly. The discs were wedged into the channeled ends. The small door was mounted as shown in section, b limensions and construction ing such that the door was well balanced. After oeing closed by tilting tne tube h?v/V/V/y/w,i it just remained closed when the tube was in a horizontal position, and could be opened by tilting the tube into a vertical position. The mounting' of the tube, and the joint J-, permitted the opening and closing of this doer even while the tube was being evacuated. The dimensions of the cathode were as follows: Outer cylinder: length ; diameter (outer) 3.54 cm. Inner cylinder: length l.g diameter (out .r) 3.38 cm. imeter of apertures The anodes were made of small aluminum rods sealed through the glass with tungsten. A bead of special Corning glass was first formed upon the tungsten wire. To this bead was fused- a short tube ■ m3 ) . glass was then fused onto the the anode. The terminal for the cathode was a plain platinum seal through the common glass of the terminal plug. The tips of ail the electrodes were protected by placing corks over them, and joining on flexible i copper leads made of -several strands of fine wire. • cem . — The bulb whi contained the suj of helium, and the system of stop cocks for letting small quantities out , are shown in Plate IV. was joined to P^ through a capillary tube for sealing off. >pe . - r constant deviation -spectr - scope, irith an illuminated pointer eve-piece was used in makin- the observations. 7 IV. MANIPULATION A. Mounting the Tube .- Photograph II shows the general set-up of the apparatus for priming the tube, The mounting was so made that the tube could be turned in order to open or close the small sathode during the process of exhaustion. It shoul be noted also that sufficient flexibility was allowed to r> revent toe much strain on the ground joint., J 3 . This flexibility was obtained by suspending the unit shown in Plate II by means of a spring sus- pension. B. Procedure for Priming .- A Xnipp mercury vapor pump , support ed by a Cenco-Nelscn Hyvao oil pump, was used to pump out the sys- tem. Before introducing helium into the tube, the pumps were al- lowed to run several hours, and at tne same time both of the char- coal bulbs. Bn and B 2 , were heated with Bunsen burners to drive out all occluded gasses. In heat.in larcoal bulbs, care was taken net to get them too hot and soften the glass. All lubricated joints were carefully protected from the heat by asbestos. The mercury vapor pump was put into operation only after the oil pump had reached its limit. At all times when the mercury vapor pump was in operation, liquid air was kept on the trap, B 3 , to prevent any mer- cury vapor from entering the tube from the pump. Now, wit Q Qg, and Qg closed, the tube was thoroughly out- gassed, and the mercury vapor pump all to carry ti acuum to hj ainable point. Then CV, was closed, t,: at removed from Bg, and the pumps were stopped. The ap] cat us was then ready for the introduction of the helium. This was done as follows: Q5 was opened for a moment and then closed. Q4 ".'as next , al- lowing a "dose” of helium to pass into the tu >e. Q4 was then closed II — — 8 again. The quantity cl’ helium introduced was regulated by the numb s ! of Mdses” g . ext, liquid air was put on Bg, and B| ■ t ed more. Bg removed all impurities from the helium, while the phos- phorous pent oxide bulb, B4, removed all water vapor. When the posi- tive rays appe quite red, was closed, the heat removed from q, and the ao.i from By. - xt was closed, and the priming unit sealed c ff at P^P<. - ■ . with fairly purs, dry helium. C* i'c^ai ay tne Qb s ervat 10ns . - The Hilger cons spectroscope was used. Some of one readings • - direct, as indicated, and the others were made by focussing the de- 1 sired beam by a lens and casting a sharp image upon the slit. This ! gave brighter lines. Many of the lines were too faint to make accu- rate observations. . * * . . V. DATA A. Ob s srvat i one . - I. Positive ray viewed lengthwise with the slit of the cathode focussed upon the slit of the spectroscope: o A units color Intensity Standard Element 6710 red F 6708 ? Li ? 5880 yellow VE 5890 Na 5047 green VF 5847,8 He 5017 green VB 5015, 7 He 4833 green F 4833 He 4713 blue VF 4713 He 4471 violet VF 4471,6 He 4387 violet VF 4388 He Ii. Cathode ray - viewed lengthwise with th e slit of the oath- ode focussed upon the slit of the spectroscope: 6711 V 5890 VE 5043 VF 5016 VB 4931 B 4711 VF 4470 F 4388 VVF III. netrograde ray - viewed diagonally, cathode ray deflected. tne retrograde ray being focussed upon the slit of the spectroscope 5830 F 504S VF 5013 B 4919 F 4709 VVF 4470 F IV. Undeflect e& Cathode Hay - viewed sidewise, and direct with-! out focussing lens: 5890 B 5053 VF 5015 B 4323 VF 4711 VVF 4471 VVF . . . . 10 V. Retrograde ray - viewed side-wise, cathode ray deflected, an direct without focussing lens; 5890 VF 5017 B 4S21 VF 4731 VVVF VI. Positive ray - viewed side- and direct without focussing lens: 5890 F 5014 B 4933 VF 4465 VVF VII. Cathode 1 ■ viewed siae^ of the spectroscope: 58S0 B 5051 VF 5017 VB 4921 F 4863 VVF 4712 VF 4471 B 4388 VF VIII. Positive ray - viewed sid< ed, focussed upon the slit of the sp 58S0 B 5048 VVF 5015 VB 4331 VF 47X3 VVF 4468 VF E . Table for Coin-far is on . - I II III IV V VI VII VIII C ol or El ement 6710 6711 — — ■ red Li? 5830 5890 5890 5830 5890 5890 5890 5830 yellow Na? 5047 5049 5049 5052 - — — 5051 5048 green He 5017 5016 5013 5015 5017 5014 5017 5015 green He 4932 4921 4313 4922 4331 4922 4931 4921 gr een He 4713 4711 4709 4711 4730 — 4712 4712 blue He 4471 4470 4470 4471 — 446 5_ 4471 4468 v i ol et He 4387 4388 — 4388 vi olet He I. Positive ray - v i ew ed lengt hwise with the slit of the * ode focussed upon the slit of the spectroscope: II. Cathode ray - viewed lengthwise with the slit of the cath- ode focussed upon the slit of the spectroscope: III. Retrograde ray - viewed diagonally, cathode ray deflected, the retrograde ray being focussed upon the slit of the spectroscope:, IV. Undeflected Cathode ray - viewed sidewise, ai out focussing lens: V. Retrograde ray - viewed side-wise, cathode ray deflected, and direct without focussing lens: VI. Positive ray - viewed side-wise, negative ray undeflected, and direct without focussing lens: VII. Cati . glow - viewed side-wise, focussed upon the slit of the spectroscope: VIII. Positive ray - viewed side-wise, negative rays undeflect- ed, focussed upon the slit of the spectroscope: ■ . ' . ‘ ■ 13 VI. CONCLUSIONS The chief difficulty in making this investigation was to get a Learn intense enough to give a bright spectrum, in order to make ac- iings. From the very nature of the rays and the manner in which they are produced it is impossible to get a ray nearly so in- tense as the positive ray. Much time was spent trying to get an in- tense beam, by varying the quantity of helium. Too much helium caus es diffused rays which mask the retrograde ray, while too little does net give a distinct beam. In the tube finally used the beam extended about three-fourths of the way across the bulb, and the bulb was fairly clear from diffuse and reflect ays. To the naked eye the beam of the positive ray and of the retro- grade ray appeared slightly different, the latter appearing a mere purplish tinge. than the former. The writer thinks this was due to the difference in the intensity of the two beams. All the observations showed distinctly the yellow sodium line ( 5890 ). In the two observations where the inside of the cathode was fo- cussed on the slit a red line, apparently lithium, appeared. This must be due to phosphorescence on a slight amount of impurity of lithium. In all, seven different helium lines appeared, while for the retrograde rays only three were present. Those lines not present for tne retro - / ray were faint lines i the other observations. All of the lines that were present in the retrograde ray were also present in the positive ray. In conclusion, I wish to express my appreciation to Professor C.T. Knlpp for the interest and assistance given in this " . ■ . I ifl ' a 1 . . . . ■ _ investigation and ^Isc to thank Professor A.P. c . .. for the facili ties of the laboratory. __ — UNIVERSITY OF ILLINOIS-URBANA 3 0112 108856573