FLAME REACTIONS O F SELENIUM AND TELLURIUM BY HARRY B . WEISER AND ALLEN GARRISON
In a recent communication, Papishl has extended the observations of Bancroft and Weiser2by showing that elementary selenium and tellurium can be precipitated on a cold object from flames charged with compounds of these elements The introduction of compounds of both selenium and tellurium into the hydrogen-air flame imparted characteristic flame colorations in distinct zones. Analogous to the conclusions reached by Bancroft and Weiser, Papish concluded that “processes of dissociation, reduction and oxidation are back of the luminescences in the different zones.” The investigations were not carried to the point where it could be said with any degree of certainty what specific chemical reaction was responsible for a given luminescence. This seemed unfortunate, particularly in view of the fact that the colorations of the different zones in the flames of selenium and tellurium were apparently quite sharply defined. Accordingly, this investigation was undertaken to determine if possible the causes of the different luminescences. The experiments with selenium will first be considered.
Experiments with Selenium The Hydrogen-imzir Flame.-Papish introduced elementary selenium and the oxide and hydride of the element into the hydrogen-air flame and obtained the results given’ in Table I. For the purpose of familiarizing ourselves with the various colors as well as their location in the flame, the experiments of Papish were repeated and extended: Hydrogen from a cylinder was passed through a horizontal hard-glass tube, the end of which was bent upward and supplied with a platinum tip approximately 4 mm in diameter. The hydrogen was 1
2
Jour. Phys. Chern., 22, 430, 640 (1918). Ibid., 18,213,281 (1914)-
Flame Reactiow of Seleaium
avld
Tellurium
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TABLEI Substance volatilized
Luminescence
I I Deposit Lumines- Deposii on cold object
1
I
Pale blue Se SeOz Deep blue Se HzSe Very faint blue None Deep blue Se Violet Se Blue Se Se
Luminescence
Deposit on cold object
Greenish1 None Greenish None Greenish2 None
ignited at the tip and the flame was adjusted to a height of approximately IO centimeters. By heating the metal or its salts in the hard glass tube, the vapors were carried into the flame in the stream of hydrogen and imparted to it three quite distinct colors in different regions: First, blue in the inner region surrounding the zone of unburned gas; and a deeper shade of blue in an outermost shell seeming to be not more than 4 mm in thickness. This shell extended from the base of the flame to two-thirds of the distance to the tip. Second, a reddish coloration in a mantle between the colorations of blue. Third, a greenish tip. Selenium may be precipitated as a red coating on a cold object such as a porcelain casserole held in certain portions of the flame. In this manner it was found that free selenium existed in the inner blue and the red portions of the flame but not in the greenish tip. From this tip white fumes of selenium dioxide were seen to rise. The pure oxide was condensed as a film on a cold sheet of mica held in the tip. The flame luminescences were quite noticeably affected by varying the amount of substances introduced into the flame.3 When only a very small amount of a substance was added, the blue color in the inner core appeared paler blue and the red luminescence was absent. The addition of an excess of the dioxide cooled down the flame and the white fumes modified the blue coloration. An excess of elementary selenium likeBecomes red if much selenium dioxide is volatilized. Occasional red flashes. Bancroft and Weiser: LOC. cit.; cf. Mitscherlich: Pogg. Ann., 487 (1864); Wiillner: Ibid., 120, 164 (1863); Wied. Ann., 8, 599 (1879).
121,
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wise modified the blue coloration and increased the amount of red luminescence. The effect of cooling the flame was quite marked: When a coil of heavy copper wire, previously cleaned, was placed around the flame, thus conducting away part of the heat, the green and reddish colorations faded leaving the blue predominant. A somewhat similar effect was prgduced by compressing the flame longitudinally between two cold sheets of mica. Since the latter is transparent it was possible toview the flame as if a longitudinal section had been cut from the center. Because of the cooling effect the red and green disappeared entirely, leaving the section of the blue flame with a dark inner core of unburned gas. When the flame was compressed horizontally by a single sheet of mica, it could be viewed from above. The cooling caused the red and green light to disappear leaving a dark center of unburned gas surrounded by a ring of blue light that was deeper blue around the outer edge. Selenium chloride and selenium bromide imparted to the flame the same colors as the metal and the oxide. It will be noted that in the main our observations confirm those of Papish except that the latter did not call particular attention to the marked effect on the coloration of varying the amount of materials added to the flame. As pointed out this not only affects the flame temperature and hence causes a variation in the velocity of certain reactions; but it also modifies the flame colorations. When there is a possibility of more than one color of light being produced in a flame, each color has an apparent influence on the others so that what is actually seen is the resultant mixture of colors. In certain regions of the flame one reaction may predominate to such a degree that the modification is altogether inappreciable; while in other regions, the effect may be so marked as to indicate a distinct luminescence. The violet coloration observed by Papish in the flame charged with selenium was not a distinct luminescence but was a mixture of red and blue in the right proportion to make violet.
Flame Reactions o j Selelzium and Tellurium
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The effect of varying the amount of substance added to the flame was brought out quite clearly in an experiment with hydrogen selenide. A method similar to that used by Papish was employed in this experiment : Hydrogen from a cylinder was conducted through the side arm of a 500-cc. suction flask containing zoo cc of water. The flask was fitted with a twohole rubber stopper-supplied with a funnel tube that dipped below the surface of the water and with a platinum-tipped glass tube. After lighting the hydrogen at the tip, aluminum selenide was introduced into the flask through the funnel tube. The selenide reacted with water evolving hydrogen selenide which was burned with the hydrogen. In the presence of but little hydrogen selenide the inner zone appeared faintly blue as Papish observed. When the amount of hydrogen selenide was increased by opening the flask and adding to it a quantity of aluminum selenide, the entire flame was quite similar to those previously observed. The inner zone assumed the same blue color and from this region elementary selenium was precipitated as in flames charged with the metal or the oxide. Particular attention should be called to the shell of deep blue around the outermost portion of the flames to which selenium or its compounds were added. This might easily be overlooked. The Bunselz Flame.-Selenium and its salts were introduced into the Bunsen flame by volatilizing them in a stream of air which was led into one of the air ports a t the base of the burner. The colorations produced were similar to those in the hydrogen-air flame. As before, the blue luminescence around the inner core seemed paler than that nearer the outside of the flame. In order to determine whether this was due to the colored zones through which the observations were made, the two cones of the flame were separated by means of the Smithells’ separator. It was observed that the sheath of blue surrounding the inner core was distinctly paler blue than the luminescence in the outer zone where oxygen was in excess. The Air-in-hydrogen Flame.-The experiments with the
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flame of air burning in hydrogen were carried out in an apparatus constructed and manipulated as follows: A hole one centimeter in diameter was blown in the bottom of a IOOOcc round bottom flask and was supplied with a platinum tip. The flask was inverted and held in place by a clamp. The one-hole stopper in the neck was supplied with a platinumtipped inlet tube that could be moved up and down at will. Hydrogen was conducted into the flask through a side arm blown in the neck; and air through the tube in the stopper, After washing the flask free from air the hydrogen was ignited at the tip. The air-inlet tube was then forced through the flask into the flame and a gentle current of air turned on. A flame of air burning in an atmosphere of hydrogen was obtained simply by drawing the air-inlet tube down into the flask. When selenium or its salts were introduced into this flame by vaporizing them in the current of air, i t was found that there was no green coloration and but very little red in the flame. There was, however, a narrow blue mantle which clung closely to the inner care where air was in excess. I n an experiment to be described later on, it was found that the red luminescence resulted in part from the glowing of the vapors of elementary selenium. Since this reddish glow was not apparent in the outermost part of the flame where selenium was in excess, it was evident that the temperature in this region was not sufficiently high. An attempt was made to raise the temperature of the entire flame by substituting oxygen for air. This was found to be impracticable, however, since the glow from the highly-heated platinum tip masked the luminescence. The Chlorine-iuz-hydrogen Flame.--In order to determine whether oxygen was necessary for securing the blue luminescence, telluric chloride was introduced into the chlorine-inhydrogen flame obtained by substituting chlorine for air in the apparatus described in the preceding paragraph. Some metallic tellurium was placed in a hard glass tube through which the stream of chlorine passed. On heating, the element was converted into the chloride which was swept into the flame imparting to the outer mantle a distinct blue coloration un-
Flame Reactions oj Selenium and Tellurium
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mixed with red or green. The coloration in the inner zone was masked by the greenish yellow hydrogen-chlorine flame. The Lumi.tzescence o j Selenium Vapors.-Since the vapors of selenium are colored one should expect them to glow when heated as do the vapors of i0dine.l As a matter of fact, Evershed found this to be the case. To determine the intensity and color of this luminescence a few grams of selenium were placed in the bottom of a hard-glass test-tube 2 cm in diameter and 2 5 cm in length. The element and the tube above it were heated until the selenium boiled vigorously. The heated vapors coming in contact with the hot tube emitted a reddish glow which corresponds to the reddish luminescence observed in the hydrogen-air flame. These observations were made in the dark room and the flame which was used to heat the element was extinguished to make sure that the vapors were actually glowing instead of reflecting light. Combustiow of Selenium-When selenium was heated in air or hydrogen it burned with a blue flame. The experiment was carried out as follows: Two grams of powdered selenium were placed near the center of a piece of hard-glass tubing 2 cm in diameter and 35 em in length. Oxygen from a cylinder was passed slowly over the metal while it was being heated with a blast lamp. When the temperature was sufficiently high the selenium burst into a blue flame of a shade identical with that in the hydrogen flame charged with selenium compounds. When more strongly heated a reddish glow appeared just above the surface of the element. By heating the tube to a greater length i t was found that the tip of the blue flame became greenish. White selenium dioxide was formed and deposited in the cooler portion of the tube. In order to determine whether the reverse reaction of reduction emitted a characteristic glow, an intimate mixture of selenium dioxide and aluminum powder was heated. The speed of the reduction was vaned by varying the relative Evershed: Phil. Mag., 5 , 39, 46j (1895); cf. Paterno and Mazzucchelli: Atti. accad. Lincei, [SI 17, 11, 428 (1908); Bancroft and Weiser: Trans. Am. Electrochem. SOC.,25, 121 (1914).
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amounts of oxide and aluminum; but in no case was a characteristic luminescence obtained. The Color of Seleniunz Dioxide Vapors.-From the above experiments it was suspected that the greenish coloration appearing in the tip of the hydrogen flame must be connected in some way with the oxide after its formation which was complete in the blue flame. The fact that the oxide but not the element could be precipitated from the greenish tip also pointed to this idea. The color of the heated vapors of selenium dioxide were observed by sealing a few grams of the oxide in a hard-glass tube in an atmosphere of oxygen and heating in a blast. At a comparatively low temperature the oxide vaporized filling the tube with a greenish yellow color. On cooling the greenish color faded and the white crystals of the oxide redeposited on the walls of the tube. Experiments with Cathode Rays.-In order to study further the luminescent reactions of selenium, the action of cathode rays on the element and its oxide were tried. Lewis1 studied the effect of cathode rays on certain metals in a cathode tube constructed in such a manner as to isolate the effect of the cathode rays from the effect of the current. Under these conditions, with elementary sulphur, selenium and tellurium he obtained “an almost imperceptible blue glow.” The cathode tube used in these experiments consisted of a vertical portion into which was sealed the disk anode and the cathode; and a horizontal portion enlarged into a bulb below the cathode. One end of the horizontal portion was constricted and to it was sealed a stop-cock tube which connected with the pump. Substances were introduced into the apparatus from the opposite end of the tube which was closed with a cap making a ground-glass connection. The tube was evacuated with a mercury pump. With substances having a low vapor pressure at ordinary temperatures, no difficulty was found in getting and maintaining a cathode vacuum with this apparatus. The bottom of the cathode tube was first covered with a layer of crystalline selenium, after which the entire apparatus 1
Astrophys. Jour., 16,3 1
(1902).
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485
including the pump was filled with hydrogen. This was done for the purpose of excluding oxygen. The surface of the metal apparently did not luminesce under the influence of the cathode rays; but the vapors throughout the bulb emitted a reddish glow very similar to that obtained by heating the vapors. Under the influence of the rays the metal volatilized and red amorphous selenium was deposited on the sides of the tube. In this experiment as carried out no attempt was made to isolate completely the effect of cathode rays from the effect. of the current and the latter unquestionably has some effect. It should be stated, however, that no reddish glow was obtained in a “blank” experiment in which the cathode tube contained nothing but hydrogen. The effect of the presence of oxygen on the luminescence was next tried by introducing oxygen into the cathode tube before carrying it down to a cathode vacuum. The presence of oxygen introduced a blue luminescence along with the red which gave a violet effect similar to that obtained in the flame. The element was then removed and selenium dioxide put in its place. Under the influence of the rays a portion of the oxide dissociated and the recombination produced throughout the tube a blue luminescence1 that was distinctly more marked than in the previous case where only a trace of oxygen was present. When the deep blue color was present, selenium dioxide collected as white crystals on the sides of the cathode tube. It was thought that a sudden lowering of the pressure while the discharge was passing might withdraw some oxygen leaving selenium in excess. To accomplish this the cathode tube was shut off by means of the stopcock and the space between the tube and the pump was evacuated as low as possible. When the stopcock was opened the pressure in the tube was suddenly diminished and immediately the blue color became a violet showing the presence of red luminescence ; and amorphous selenium deposited on the tube instead of the oxide. If the bombarding was conWiedemann and Schmidt: Wied. Ann., 56, 243 (1895); Wilkinsoa: Jour. Phys. Chem., 13, 691 (1909).
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tinued more oxide was dissociated and the violet gradually gave place t o blue. In order to show that compounds other than the oxide would give a blue luminescence in the cathode tube, an attempt was made to use selenium tetrabromide and selenium tetraiodide. Owing to the volatility of these compounds it was found impossible to get a cathode vacuum at ordinary temperatures. Discussion of Results The three colorations in the flames of selenium will be considered separately : The Blue Luminescewe.-Blue luminescence is produced under the following conditions: ( I ) When elementary selenium burns in excess oxygen. ( 2 ) Pale blue in the region surrounding the inner cone of the hydrogen-air flame or the Bunsen flame charged with selenium, its oxide, hydride or halides. In this region air is present but not in excess. (3) A deeper blue in the outer portion of flames in air where there is excess oxygen. This is particularly marked in a sheath surrounding the outermost portion of the lower part of the flames. (4) A narrow mantle close to the inner core of the air-hydrogen flame. ( 5 ) In the flame of chlorine burning in hydrogen. (6) When the oxide is acted on by cathode rays. From these results it is evident that the blue color is always produced when the element is oxidized rapidly enough. Air is unnecessary since the same coloration is obtained in an oxygenfree flame. The lowest oxide of selenium is the dioxide and this is formed when the element is burned in air or oxygen. When the oxide is acted on by cathode rays a blue lurninescence is produced from which it seems probable1 that the specific chemical action that produces the color is the reaction from selenic ion to selenic oxide or salt. The depth of the blue color depends on the amount of selenium oxidized in a given space and the rapidity of the oxidation. This accounts for the blue luminescence appearing Wiedemann and Schmidt: LOC.cit.; Wilkinson: Loc. cit.
Flame Reactions of Selenium and Tellurium
487
paler in the inner portion of the hydrogen flame than in the outer portion where there is excess air. When selenium salts are introduced into the ordinary flame they are so readily acted on by the combined dissociating and reducing actions of the flame that some selenium is formed a t once and can be precipitated on a cold object held but a short distance from the inner zone of unburned gas. This selenium coming in contact with a relatively small amount of oxygen a little further on, burns in part with a blue luminescence. Beyond this narrow zone in the hottest region of the flame the reverse reaction of dissociation predominates but this gives place to oxidation again in the cooler outermost portion of the flame. This last oxidation takes place in the presence of excess air and the luminescence appears deeper blue than it does in the inner zone. If the amount of selenium added to the flame is very small, only a faint coloration appears in the inner zone. On the other hand, the presence of an excess of the element or compound cools the flame and masks the coloration in proportion to the amount present. The bluest color in the inner zone should result in the presence of the maximum amount of selenium that is capable of complete oxidation before reaching the zone of highest temperature where the reverse reaction predominates. The Red Luminescence.-The red luminescence is produced under the following conditions: ( I ) In the hottest portion of flames charged with excess selenium or its compounds. This is most marked midway between the inner and outer cones. Elementary selenium is readily precipitated from this portion of the flame. (2) When the highly colored vapors of selenium are heated. (3) When selenium vapor is acted on by cathode rays in a hydrogen-filled cathode tube. Since the vapors of selenium are colored it is evident that a t least a part of the luminescence on heating the vapors is a thermal luminescence; but in view of the fact that a similar glow was obtained in the cathode tube, it is probable that a part of the glow is due to chemiluminescence. A similar
Harry B. Weiser and Allen Garrison
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conclusion was reached concerning the luminescence of heated sodium vapor. In all probability this is due in part to thermal luminescence1 and in part to chemiluminescence. In connection with the flame reactions of sodium, the evidence indicated3 that the familiar yellow luminescence was produced a t least in part by some stage in the reaction from electrically neutral sodium vapor to sodium ion. It was impossible to specify the reaction more closely since it was not possible to account for all the sodium spectra observed by Lenard4 and by Wood and Galt.5 Similarly, we conclude that the red luminescence in the flames containing selenium is due in part to the color of the vapors, in part to a purely thermal luminescence and in part to some stage in the reaction from electrically neutral selenium vapor to selenic ion. It is as yet unsafe to specify the reaction more closely particularly since no quantitative study of the glow spectrum of selenium vapor under various conditions has been made as in the case of sodium vapor. In this connection Lenard6 has shown the existence of selenium ions in the hottest portion of flames but not in the outermost regions. As previously pointed out, the amount of the red luminescence is determined by the amount of selenium added to the flame. The coloration may be eliminated almost completely by encircling the flame with a spiral of large copper wire. The part which each of the above mentioned factors contribute to the red luminescence can be decided only by a quantitative study of the flames under various conditions. The Greenish Coloration.-The greenish coloration occurs : (I) In the outer tips of the hydrogen-air and the Bunsen flames. (2) When selenium is vaporized in a sealed tube. Although solid selenium dioxide is white, the vapors are greenish from which we conclude that the green color in the tip of certain flames is not a luminescence a t all but is merely the Evershed: LOC.cit. Wood: “Physical Optics,” 537, 579 (1911). 3 Bancroft and Weiser: Jour. Phys. Chem., 19,310 (1915). Drude’s Ann., TI, 636 (1903). 6 Astrophys. Jour., 33, 72 (1911). 6 Drude’s Ann., 9, 632 (1902). 1
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color of the dioxide vapors that appear more green because of the reflection of the blue luminescence just below. On cooling the flame the green coloration disappears, since the vapors are converted to a white smoke. A similar phenomenon was observed in the hydrogen-chlorine flame charged with copper salts and in the Bunsen flame charged with a large excess of copper chloride' The vapors of the chloride are colored and impart a coloration to the tip of the flame.
Experiments with Tellurium By introducing tellurium compounds into the flame of hydrogen burning in air Papish2 obtained the results given in Table 2. TABLEI1 Inner zone Substance volatilized
TeOz HzTe Te
Luminescence
Deposil on cold object
Green Blue Green
Te Te Te
Middle zone
Lilac3 Lilac Lilac4
Te Te Te
Outer zone Luminescence
Deposit on cold object
Green Green Green
Kone None None
The Hydrogen-in-air Flame.-The experiments with the hydrogen flame were carried out in the same manner as previously described for selenium. The flame charged with the element and its compounds consisted of three distinct colors with sometimes a fourth: First, green in the inner cone surrounding the zone of unburned gases; second, an outer mantle of blue that could be modified considerably by the addition of varying amounts of material to the flame; third, a greenish tip; and fourth, in some instances a shade of red between the outer blue and the inner green in the hottest portion of the flame. Tellurium was precipitated as a metallic mirror when
* Bancroft and Weiser:
Loc. cit. Loc. cit. a Accompanied by red flashes. 4 Also red surrounded by blue when much tellurium is volatilized.
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B. Weiser avtd Allm Garrison
a cold object such as a porcelain casserole was held in the inner green or the reddish portions of the flame. It will be seen by referring to the above table that in most respects our observations agree with those of Papish. The so-called lilac color observed by the latter was not a distinct luminescence but was a mixture of blue and reddish orange in the right proportions. As was true with selenium flames, the respective colors can be modified considerably by varying the amounts of materials added to the flames. Thus Papish ordinarily obtained a lilac coloration but with excess of selenium he got the reddish luminescence surrounded by blue as we observed. A particular instance of the effect of the quantity of material introduced into the flame was again brought out in the experiments with the hydride. The experiment was carried out as previously described for hydrogen selenide substituting aluminum telluride for aluminum selenide. A considerable quantity of aluminum telluride was added to the flask and no difficulty whatsoever was experienced in getting a flame with the inner green region similar to the flames to which the metal was added. It was only after the telluride was almost gone that the inner zone took on more of the bluish color noted by Papish. This same effect was produced by adding a trace of the element to the flame. As will be pointed out in the subsequent discussion of these experiments, these results are in accord with what one might expect. The effect of cooling the flame was quite as marked as in the case of selenium. When a spiral of large copper wire was lowered around the flame thus conducting away some heat, the greenish tip faded and all reddish coloration disappeared leaving only the green inner core surrounded by a mantle of very deep blue. When compressed longitudinally between two sheets of mica,. the orange reddish luminescence and the green tip again disappeared. The section, appearing as though it had been cut from the center of the flame, consisted of a dark core of unburned gas along the sides of which was a narrow strip of green, followed by one of blue. By compressing the flame horizontally with a single sheet of mica and observing
Flame Reactions of Selenium and Tellurium
491
from above, the section was seen to consist of a dark center of unburned gas surrounded by a circle of green and a narrower rim of blue. Tellurium dioxide was deposited as a white ring outside the circle of flame. From this it seemed likely that tellurium dioxide could be precipitated on a piece of mica held in the greenish tip of the flame. This conclusion was confirmed as the oxide is much less volatile than the corresponding oxide bf selenium and was readily condensed. The molten oxide as well as the vapors were found to be greenish yellow in color. The Bunsen Flame.-The Bunsen flame contained the same colorations as the hydrogen flame. When the two cones were separated in the Smithells’ separator, the Anner flame, where air was not in excess, formed a sheath of vivid green unmixed with blue, surrounding the cone. The outer flame where air was in excess was blue with a greenish tip. The latter was less marked than in the ordinary hydrogen flame probably on account of the lower temperature. Por the same reason there was but little reddish in the flame. A more brilliant coloration in both zones was obtained by using volatile salts of tellurium such as telluric bromide and telluric iodide. With these salts were produced an inner flame of very vivid green and an outer deep blue with a faint greenish tip. The Air-in-hydrogen Flame.-When tellurium was introduced into the flame of air burning in hydrogen, the inner core surrounding the zone of unburned gas was blue and around it was a mantle of deep green like that observed in the inner zone of the Smithells’ separator. Metal deposited on the walls of the bulb. The Chlorine-in-hydrogen Flame.-Chlorine was passed over heated tellurium and the telluric chloride formed was swept into the flame of chlorine burning in hydrogen. An outer mantle of green was obtained identical with that in the same region of the air-hydrogen flame. The inner blue core was indistinct as it was masked by the yellowish chlorine flame. Combustion of Tellurium.-A few grams of tellurium were placed near the center of a hard-glass tube through
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which was passed a slow current of oxygen. The tellurium was heated until it burst into a flame the color of which was greenish blue. The line of separation between the two colors was much less distinct than in the hydrogen flame. However, the flame was more green near the tellurium where the metal was in excess and more blue where oxygen was in excess. By heating to a high temperature i t was possible t? .obtain the golden yellow vapors of tellurium just above the surface of the element. White tellurium dioxide was deposited on the tube beyond the flame. Since in all cases the green luminescence was formed in the more reducing portions of flames and the blue in the more oxidizing regions, it should be possible to decrease the green luminescence to a minimum and to increase the blue luminescence to a maximum by increasing the concentration of oxygen in the region of the hydrogen flame charged with tellurium. To obtain this condition, the platinum-tipped hydrogen tube was jacketed by a tube 3 cm in diameter and I O cm in length. A stopper in the bottom of this jacket-tube served the double purpose of closing the bottom and of holding it concentric with the hydrogen tube. The top of this jacket was about 2 cm above the hydrogen tip. After lighting the hydrogen and introducing tellurium into the flame, oxygen was run into the jacket from a side arm near the bottom. The oxygen arose and encircled the lower portion of the flame supplying it with an excess of the gas. Under these conditions the flame became almost entirely blue with only a small reddish orange inner core and the usual greenish tip. No characteristic luminescence was obtained by the rapid reduction of tellurium dioxide with aluminium powder. Cathode Rays ow Tellurium and its Salts.-The experiments with the cathode rays were carried out in the same apparatus as previously described. Metallic tellurium was first introduced into the hydrogen-filled tube which was then evacuated. The glow in the bulb was reddish under the influence of the rays but the coloration was not so marked as with selenium on account of the greater volatility of the latter
Flame Reactions of Selenium and Tellurium
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metal. When the metal was replaced by the oxide a faint bluish glow was obtained. Telluric bromide was next used with more marked results. When the salt was first bombarded a reddish glow was produced over the surface which soon disappeared, and did not return. The vapors throughout the bulb glowed with a bright blue color but the luminescence was green near the surface of the bromide. Since the cathode ?ays decompose the compound into its elements and since tellurium is much less volatile than bromine it seemed plausible, in line with previous experiments, to attribute the blue luminescence throughout the bulb to a relatively higher concentration of bromine and the green luminescence near the surface of the salt to a relatively higher concentration of tellurium. If this were true it should be possible to exhaust further during the passage of the discharge thereby decreasing the concentration of bromine. This was done as in the experiment with selenium dioxide and it was found under suitable conditions that the luminescence throughout the bulb changed from blue to green. The discharge was continued and after a time the green disappeared giving place to the usual blue as more telluric bromide was decomposed by the cathode rays. It was hoped to confirm these experiments with telluric iodide; but the salt was so volatile that a cathode vacuum could not be obtained at ordinary temperatures.
Discussion of Results There are four colorations in the flames of tellurium to be accounted for. These will be considered in turn: The Green Luminescence.-The green luminescence is produced under the following conditions: (I) In the inner zone of the hydrogen-air flame and the Bunsen flame charged with tellurium compounds. With volatile salts of tellurium such as the bromide and iodide, this coloration is particularly marked in the zone surrounding the inner core of the Smithells’ separator. (2) Deep green outer zone in the flame of air burning in hydrogen. (3) Deep green outer mantle in the flame of chlorine burning in hydrogen. (4) Near the surface
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of the tellurium when the element is burned in oxygen. ( 5 ) Under the influence of cathode rays telluric bromide shows a green luminescence near the surface of the salt where tellurium is in excess. By suddenly lowering the pressure in the tube while continuing the bombarding, bromine is withdrawn and green luminescence fills the tube. Tellurium differs from selenium in that it forms two oxides TeO and TeOz and series of salts corresponding to both oxides. When the element is burned in air or oxygen it goes to the dioxide; but it is altogether probable that the oxidation is stepwise although it does not stop at the monoxide stage. A stepwise oxidation is readily carried out with the halogens. By reference to the data above summarized it will be seen that the green luminescence occurs in the more reducing portions of flames which favor the reaction to tellurous compounds. This is true in every case whether the oxidationis in the presence or the absence of oxygen. Since the green luminescence is obtained in the cathode tube under the conditions which favor the formation of tellurous salt we conclude that the green luminescence in tellurium flames is due t o the reaction from tellurous ion to tellurous salt. The Blue L.uunilzescelzce,-The blue luminescence is produced under the following conditions: (I) I n the outer zone of the hydrogen-air flame and the Bunsen flame charged with tellurium and its compounds. (2) In the inner zone of the flame of air burning in hydrogen. (3) The flame of tellurium in oxygen. (4) Throughout the greater portion of the hydrogen flame charged with selenium compounds when the lower portion of the flame is encircled with an atmosphere of oxygen. (5) Throughout the cathode tube containing telluric bromide when bromine is in excess. From the above data it is evident that the blue luminescence occurs in the oxidizing portion of all flames which favor the formation of telluric compounds. Since the cathode rays on telluric compounds give a blue luminescence under suitable conditions, we conclude that this luminescence is due chiefly to the reaction from telluric ion to telluric salt.
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As in the case of selenium flames the coloration is influenced by the amount of material present in the flame. If but a trace of the element is added to the hydrogen flame complete oxidation may take place in the inner zone which may then appear more blue than green in color. In the presence of excess selenium the blue luminescence is modified by reddish giving it a lilac appearance. If the flame is cooled by surrounding it with a coil of wire the reddish color disappears leaving a decided blue. The Reddish Luminescence.-The vapors of elementary tellurium are golden yellow in color and when heated in a quartz tube Paternb and Mazzuchellil found that an emission spectrum is produced which they considered was a temperature radiation. A reddish glow is obtained with the element in a cathode tube filled with hydrogen before evacuating. Analogous to the reddish luminescence in selenium flames, it is probable .that the orange red color in the hottest portion of flames from which tellurium can be precipitated, is due in part to the color of tellurium vapors, in part to thermal luminescence and in part to chemiluminescence resulting from some stage in the reaction from electrically neutral tellurium vapor to telluric ion. A quantitative study is necessary to determine the part contributed by each of these factors under widely varying conditions. The Green Coloration.-Tellurium dioxide melts to a greenish yellow liquid. The oxide is much less volatile than the corresponding oxide of selenium and the color of the vapors is not so marked. However, the greenish coloration in the tip of the flame is unquestionably due to these vapors reflecting the blue luminescence just’below them. When the tip of the flame is cooled, the vapors are readily condensed and the green coloration disappears forthwith. Summary The results of this paper may be summarized briefly as follows; LOC.cit.
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Harry B. Weiser awd Allew Garrison
( I ) A study has been made of the flame reactions of selenium and tellurium and of the salts of selenium and tellurium. (2) The reaction from selenium to selenic salt produces a blue luminescence which is the most characteristic in flames containing selenium. It is probable that this luminescence is due chiefly to the reaction from selenic ion to undissociated selenic salt. (3) The reaction from tellurium to tellurous salt produces a green luminescence; and from tellurous salt to telluric salt a blue luminescence. It is probable that the green luminescence is due chiefly to the reaction from tellurous ion to the undissociated tellurous salt ; and the blue luminescence from telluric ion to the undissociated telluric salt. (4) Under certain conditions a reddish luminescence occurs in flames containing selenium that is as a rule less intense than the blue luminescence ; and a reddish orange luminescence in the flames containing tellurium that is less intense than either the green or the blue liminescence. Since the vapors of both elements are colored, it is probable that the reddish coloration io both cases is due in part to the color of the vapors, in part to a purely thermal luminescence and in part to some stage of the chemical reaction from the vapors of the element to the tetravalent ion. It is unsafe to specify the reaction more closely until more is known of the glow spectra of the vapors of the respective elements. (5) No characteristic luminescence has as yet been detected for the reverse reactions. (6) A combination of the red and blue luminescence frequently gives a violet or lilac appearance to certain portions of the flames. This must not be mistaken for a distinct luminescence. (7) A greenish tip in the flames in air charged with selenium and tellurium compounds is not a luminescence but is due to the greenish color of the vapors of the dioxide which appear more green by reflecting the blue luminescence just below.
Flame Reactions of Selenium and Tellurium
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(8) Particular attention has been called to the modifying influence on flame colorations by varying the amount of materials added to the flame: Degartment of Chemistry The Rice Institute Houston. Texas
