ACTIVE CHLORINE BY Y.VENKATARAMAIAH
Introduction In the year 1897, W. A. Shenstone' made some researches on the activation of chlorine by tbe ozonising discharge and came to the conclusion that, highly purified chlorine is uneffected by it. I n the year 1902, Kellner2 and Vernon3 made contributions to the effect that chlorine is affected by the silent electric discharge. Again, in the year 1905, F. R U S S ~ studied the activation of chlorine by the silent electric discharge and by light. Much valuable work on the subject of active chlorine was done by M e l l ~ rBurgess ,~ and Chapman,6Chapman' and other chemists. In any case little work was done by all the abovementioned scientists, on active chlorine in regard to its chemical properties. There was also little work done to elucidate the molecular complexity of the active gas. With these in view the author has undertaken this piece of work. In the present research, the active chlorine was prepared in several ways. Although, the gas is formed in relatively small quantities, yet it is a more powerful chlorinating agent than ordinary chlorine. It is comparatively not a stable gas. Preparation of Pure Chlorine The pure chlorine needed in the experiments was prepared from gold chloride. The method of preparing pure gold chloride is described below. Pure gold obtained from the market was dissolved in aqua regia prepared from pure niJour. Chem. SOC.,71, 471 (1897). Zeit. Elektrochemie, 8, 500 (1902); cf. also Wiener Am., 12, 15 Mai. Ost. Pat. 11180, Oct. 15 (1902). 4 Sitzungsher. Akad. Wiss., Wien, 114, IIb, 194. Proc. Chem. SOC.,20, 140 (1904). Ibid., 20, 164 (1904); Jour. Chem. SOC.,89, 1399 (1906). Proc. Chem. SOC.,29, 75 (1913). l
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tric and hydrochloric acids of Kahlbaum. Gold was precipitated from the pure chlorine of gold solution prepared from the above crude solution by means of Kahlbaum's pure oxalic acid. The solutions of gold chloride and oxalic acid were kept at a temperature of 80" C in order to get a good precipitate of gold. The gold so precipitated was washed free from impurities with distilled water and was subsequently dissolved in aqua regia again. The crystallised gold chloride, after it was rendered free from impurities, was dried for a few days at a temperature of 110" C. Finally, a number of glass bulbs attached to the main apparatus as shown in Fig. 1, were charged with the pure chloride of gold (about 15 gms) ready for use. When pure chlorine was required, these bulbs were heated one by one. As the bulbs were used, they were sealed off the main apparatus.
Apparatus and Working The apparatus consisted of a series of gold chloride bulbs fused to the main apparatus a t A as shown in Fig. 1. A number of stop-cocks a t SI , Sz. . . . were used with phosphoric
Fig. i
acid. B were a set phosphorus pentoxide tubes t o dry the chlorine. At C were fused four one-litre flasks. The flasks could be heated to 200" C by means of an electrical heater. D was a spiral of glass-tube kept cool by a freezing mixture. E was a vacuum-type ozoniser about 50 crns in length. The diameter of the inner tube of the ozoniser was 2.5 crns, while the ozonising space between the tubks was 3 mm in width. The ozoniser was worked by a powerful induction coil whose
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primary could be fed up to 25 amperes with a Wehnelt interrupter as a make-and-break arrangement. Sometimes, Leyden jars with a spark-gap were used in parallel with the ozoniser with little success. F was another short coil of glass tube kept in ice-water to cool the gas from the ozoniser. G was a small tin-foil ozoniser which could be worked with a two-inch induction coil, in which ozone could be prepared. H was a small test-chamber. JJ were U-tubes kept in freezing mixture at - 25" C 11, KK, IJ, were phosphorus pentoxide, caustic potash, and calcium chloride tubes. A slow current of chlorine was sent through the apparatus either by using vacuum pumps or by making use of the electrical heater. Chlorine was generated by heating the gold chloride bulbs one by one as necessity demanded. The whole apparatus was swept with dry chlorine for a number of hours preliminarily exhausting the whole apparatus. Finally, before the chlorine gas was stored, the whole apparatus was exhausted and filled with chlorine a number of times. The hot gas from the storing vessels was passed for a long time to rid the apparatus of its moisture and then the gas was stored. When the activation of chlorine was going on a number of reagents were used to test its activity.
Properties of Activated Chlorine (1). Active chlorine combines directly with ozone1 to form C1,O. As the active gas was passing through the apparatus, the tin-foil ozoniser was set in action, which supplied a good stream of ozone. The ClzO which was formed by the interaction of active chlorine with ozone, condensed as reddish brown droplets in the U-tubes in the freezing mixture. At this stage the primary of the induction coil was consuming 20 amperes. Decrease in the secondary current meant, only a decrease in the production of ClzO which meant a decrease in the amount of the active gas formed. 1
Rendiconti Akad. Sci. Fis. Mat. Napoli, 15, 15 (1909).
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The author could not confirm the result of E. Comanducci who says that the compound produced by the interaction of ozone and active chlorine is CIOz. In the present researches i t was found that the reddish brown droplets dissolved in water forming a yellowish solution. In order to get big droplets a run of nearly 40 hours was also made. (2) The active gas when passed over cold powdered sulphur attacks it directly with the formation of S2C12. Sulphur was put in the test tube. SZCl2condensed in the U tubes as yellow oily drops. The drops dissolved in water giving rise t o S,SOz and HC1. A run of nearly 20 hours was made. (3) Active chlorine combines with fine tellurium powder a t a slightly elevated temperature giving rise to tellurium dichloride which can be decomposed by water with the separation of tellurium and the formation of HC1 and H2Te03. A run of 32 hours was made. (4) Bright metallic sodium and silver were attacked by the active chlorine. ( 5 ) Carbon in no less than six varieties was presented t o the action of the active gas but with no reaction. (6) Active chlorine attacks benzene and acetic acid even in the dark with the formation of benzene hexachloride and chloro-acetic acid. In both these cases such reactions are possible only in the sun-light. 11. Activation of Chlorine by the Electrical Discharge
Activation of chlorine by the electrical discharge was carried on in an ordinary type of vacuum tube with aluminium electrodes. The capillary tube was 5 mm in diameter and the length of the vacuum tube was 50 cm. The chlorine gas was passed through the tube at 20 mm pressure. It was found that’an increase in secondary current resulted in the increased production of the active gas. The maximum secondary current that was utilized was 40 milli-amperes. In this case also the presence of active chlorine was detected by the above-mentioned tests. The production of the active
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gas appeared to take place in a shorter time than in the above silent-electric-discharge method, as in no case was a run made of more than 30 hours. 111. Activation of Chlorine by Ultra-violet Light The activation of chlorine was carried on in a quartz tube placed between two parallel rows of iron arcs three inches apart. Each row contained five automatically adjusted arcs three inches apart, connected in parallel, and each supplied with a current of 6 amp. The whole system was enclosed in a brightly polished nickel-plated iron box, kept in a cooling bath of ice-cold water continuously running in and out. A rapid current of cold air was continuously drawn through the box. Occasionally the arcs were rendered free from any coating of iron oxide. The quartz tube was 3/4 in. in diameter and about 16 inches in length. Through the tube a slow current of pure dry chlorine was passed. The presence of active chlorine was tested as before. Here also a very long time elapsed before the presence of the active gas was detected. Runs covering a period of 32 hours were made.
(1V). The Thermal Production of Active Chlorine Since it is known that even active chlorine has no action on carbon, it was found convenient to establish an arc between two carbon electrodes in an atmosphere of chlorine. For this purpose,an arc was maintained in a glass globe between two carbon electrodes. One of the electrodes (negative) was bored through and a current of chlorine was led into the arc. The chlorine was drawn off through a side tube attached to the globe, through a coil kept in ice-cold water, and to the reagents. By this method also chlorine could be rendered active. No doubt this is not purely a thermal effect.
Activity of Chlorine The question now remains whether, the activity of the new chlorine is due to an allotropic modification of the element or to ions. The view that the activity of the gas is
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due to ions, produced by the various modes of energy, is precluded by the fact that the gas remained as active as ever whether it was made t o pass through a strong electrostatic field or not. The activity could not have been due t o any complex compound formed in the process of the activation of chlorine as suggested by Melior and others, because the gas was dried thoroughly by phosphorus pentoxide before activation and consequently was free from moisture. The activity of the gas might be due to atoms (nascent chlorine) or to some complex molecules. If the activity is due t o atomic chlorine one should expect an expansion in volume when ordinary chlorine is activated, but on the other hand if any complex molecules are formed during the course of activation, a contraction in volume is to be expected. The experimental results described below appear to lend support to the latter rather than t o the former view.
Contraetion in Volume In order to measure the contraction in volume, the author had recourse to the silent-electric-discharge method as i t is liable t o less errors than the other methods. For this purpose an ozoniser with a side tube as shown in Fig. 2 was adopted. A was a vacuum type of ozoniser. B was a capillary tube attached to it, which in its turn was attached to another capillary manometer M graduated to tenths of a millimeter. B is 0.5 mm bore while M was 5 mm in diameter. The manometer contained Fig. 2 pure dry mercury. It was shown by Shenstone that pure dry chlorine has no action on pure dry mercury. In the present arrangement there is little chance for the active gas to come in contact with the dry mercury through the capillary tube B. Keeping the chlorine, in the ozoniser at atmospheric pressure, it was found that in 10 hours a contraction of nearly 8
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mm in the manometer had occurred. The temperature of the ozoniser was kept a t constant temperature, by, means of a thermostat. After the ozoniser was stopped from working the mercury regained its original position in the manometer. This clearly shows that when chlorine is activated, a complex molecule is formed, and that the activity of the new gas may safely be traced to it. The nature of the complex body is yet to be determined. We do not know a t present how the different forms of energy-electric, actinic and thermal-act to produce this complex active gas. It seems certain, at any rate, that there exists an allotropic modification of chlorine.
Summary 1. It is shown by the author that chlorine is rendered active by the silent electric discharge, electric discharge, ultraviolet light and by heat. 2. In chemical properties this new gas is .shown to be much more active than the ordinary chlorine. I t combines with ozone to form C120,with S to form S2Clz,with tellurium t o form TeC12,with bright sodium and silver to form NaC1, and AgC1, with benzene in the dark to form CcH&Yc. 3. It is unstable and is decomposed above 50" C. 4. Chlorine contracts in volume when it is activated. 5. It is clear from the above researches that there is an allotropic modification of chlorine. Further work on the subject is now being carried on by my friend Mr. M. V. N. Swami. My best thanks are due to Prof. Y. Narasinhan, M.A., for the kind interest he has taken in the work. Calcutta July 2, 1922
