THE ACTION O F CHLORINE ON MERCURY BY ALBERT E . 0. GEBMANN
In an article on “Active Chlorine”, by Y. Venkataramaiah,’ published recently in this Journal, an apparatus is described for the measurement of the volume change occurring in a given mass of chlorine at constant temperature under the influence of the silent electric discharge. The volume change was observed on a mercury manometer, communicating with the main body of the apparatus through a capillary tube of one half millemeter bore. It is not clear from the description whether chlorine actually came in contact with the mercury, or whether this portion of the apparatus contained air, but one is inclined to believe, from the context, that chlorine and mercury were left in contact for the duration of the experiment, ten hours. The author says:“The manometer contained 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.” Mr. Venkataramaiah tacitly agrees with the statement credited to Shenstone, and one would be justified in the conclusion that he found pure dry chlorine inert towards pure dry mercury. Without wishing to belittle the importance of the work on active chlorine, my impression is that this would be far overshadowed by the feat of producing inactive chlorine. But I am frankly skeptical, and look forward to a positive statement regarding the matter with much interest. As a matter of fact, Shenstone, after performing elaborate experiments on this subject2came to the reluctant conclusion that “the action between mercury and chlorine, bromine, or iodine does not depend on the presence of water vapour.” That he had not revised this opinion a t the time of his death, is attested by his friend, Sir W. A. Tilden, whose assistant Shenstone was at Clifton College, and whose successor he became when Dr. Tilden was called to Mason College. I n an obituary notice Dr. Tilden3 said:-“The results of these experiments led him to the conclusion that chlorine, bromine and iodine when in the highest known condition of purity, dried by contact under special conditions with phosphoric oxide for six months or more; do a t once combine with mercury when brought into contact with that metal similarly purified and dried.” Y . Venkataramaiah: J. Phys. Chem., 27, 79 (1923). W. A. Shenstone: J. Chem. SOC., 71, 479 (1897). a W. A. Tilden: J. Chem. SOC., 95, 22c6 (1909).
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Similar evidence is given by Cowper,1 who found that chlorine which was inactive towards sodium even when melted, readily attacked mercury, tin, antimony and arsenic. One is inclined to attribute the action of chlorine on arsenic, antimony and tin t o the formation of liquid chlorides, and its action on mercury to the fact that mercury differs from other metals yielding solid chlorides in its liquid state, and the readiness with which a new surface is presented for reaction with the gas. But then melted sodium ought also to be attacked, and Cowper says that after some initial action, which he attributes to imperfect drying, melted sodium remains untarnished in an atmosphere of chlorine gas. A similar observation was made by Wanklyn some years before.2 While my own experiments on this subject are by no means as rigorous as those cited above, they still have some interest. I have had frequent occasion to prepare pure dry chlorine. On these occasions my secret conviction that really pure chlorine would not attack mercury always prompted me to use every precaution in the purification, and to try the experiment; but the results have been uniform-combination proceeds with undiminished vigor. It is known that phosgene does not attack metals, except a t an elevated temperature, when it is probably chlorine resulting from dissociation that is responsible for the action. Phosgene hydrolyzes in the presence of moisture, producing hydrogen chloride and carbon dioxide; while this reaction has not been shown to be reversible, it is known that concentrated hydrochloric acid retards the h y d r ~ l y s i s . ~Hence larger amounts of water are only slowly destroyed by phosgene. But small amounts of water should be rapidly decomposed by phosgene, especially at an elevated temperature. In an effort to dry my materials with phosgene, I partially filled a tube with liquid phosgene and left it for some time at room temperature, I then allowed the phosgene to boil away, and heated the tube with the free flame, evacuating the while; after several repetitions of this process, I distilled several grams of pure mercury into the tube from a side tube, which had also been subject to the phosgene and heat treatment. Several days before I had prepared in another tube a solution of pure chlorine in liquid phosgene, and kept it a t room temperature, in the hope that any traces of moisture might be destroyed. This solution was finally distilled in to the tube containing the mercury, which immediately reacted completely with the chlorine. In this experiment it is of course possible that phosgene played the usual role of water, and that the reaction was catalyzed b y phosgene, But this is extremely improbable, as Klein has shown4that in the reaction between hydrogen sulfide and sulfur dioxide, which takes place in the presence of a trace of water, the reaction is also induced by fifteen substances, including alcohols, ketones, nitriles, esters, ether and carvone, but not by carbon disulfide, ethyl
’ Richard Cowper: J. Chem. SOC.,43, 153 (1883). 3
J. A. Wanklyn: Chem. News, 20, 271 (1869). See DelBpine, Douris and Ville: Bull. 27, 286 (1920). David Klein: J. Phys. Chem., 15, I (1911).
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disulfide, benzol, amylene, chloroform, carbon tetrachloride, ethyl chloride, acetyl chloride, benzoyl chloride and nitrobenzene. Of the five halogen derivatives tested, not one was able to catalyze the reaction studied. This evidence is substantiated by the observation that chlorine dissolved in liquid phosgene does not attack magnesium. The fact that chlorine dissolved in phosgene attacks aluminium’ has no bearing on this point, because aluminium chloride is soluble in phosgene, In fact, it has been shown2 that phosgene itself reacts with metals in the presence of aluminium chloride, with which the metallic chloride produced in the reaction forms soluble complexes.
Conclusion. With the exception of the implied experience of Mr. Venkataramaiah, there seems to be no record of chlorine showing itself inert towards mercury, It would be very much worth while to have a detailed account of his research with particular reference to “inactive chlorine”. Addendum. The December number of this Journal (27, 951 1913)has an unindexed note containing corrections to Venkataramaiah’s article, which the writer has since found. I n this, besides numerical corrections which seem to diminish the certainty of some of the conclusions drawn by V., the statement is made that the manometer contained fused silver chloride instead of mercury. The writer refrains from making any comment upon this correction, and trusts the reader to draw his own conclusions. A. F. 0. G. Stanford Universiiy, California. 1A. 2A.
F. 0. Germann: Science, 58, 309 (1923). F. 0.Germann and K. Gagos: Science, 58, 309 (1923).
