MERCURIC OXIDE JELLIES BY E. H. BUNCE
This work was chiefly a repetition of that by J. Emerson Reynolds. “When a solution of mercuric chloride is added slowly t o a mixture of acetone with a dilute aqueous solution of potassium hydrate, the mercuric oxide first precipitated is dissolved, with the production of a clear colorless liquid. The addition of the mercurial solution can be continued until a white precipitate makes its appearance, the alkali being still in excess.2 If the solution be filtered at this point, an apparently opalescent, yellowish colored liquid is obt a i r ~ e d . ~If one portion of this alkaline solution be boiled for a few minutes, a thick gelatinous mass suddenly separates, and further ebullition is rendered difficult, if not impossible. Another portion of the liquid gelatinizes when treated with an acid in slight excess ; and, if the original solution be moderately strong, the.vesse1 in which the experiment is made may be inverted without risk of spilling its contents. Finally, if some of the mercuric solution be exposed over sulphuric acid in vucuo, i t leaves on partial evaporation a gelatinous mass, on the surface of which latter crystals of potassium chloride soon make their appearance. When the desiccation is complete, a yellowish resinoid body is obtained, together with a large quantity of very. beautiful acicular crystals of Proc. Roy. Soc., 19, 431 (1871). The same results can be obtained when mercuric oxide is precipitated from any of its salts, washed rapidly, and then digested with excess of acetone and potassium hydrate. The best mode of operating, however, is that stated in the text. The different solutions exhibit a slight opalescence, not completely removable by ordinary filtration. This opalescence appears to be due to the very gradual separation, a t ordinary temperatures, of traces of the same anhydrous substance which is thrown down very rapidly a t a boiling heat. I n composition the latter body is identical with the anhydride obtained by other methods and described further on.
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the chloride and a certain amount of potassium carbonate. The solution of mercuric oxide in potassium hydrate in presence of acetone takes place as easily in alcoholic as in aqueous liquids. “ Preliminary experiments similar to the foregoing were sufficient to indicate that the chief compound produced in the reaction above referred to might be regarded as a colloid body. I, therefore, took advantage of the late Professor Graham’s beautiful dialytic methodl for effecting its purification from crystalloids and have met with complete success. “As the preparation of a stro.tzg solution of the pure acetone mercuric compound suitable for dialysis is attended with some difficulty, I may now describe in detail the mode of operating proved by experience to afford the most satisfactory results. Forty grams of pure mercuric chloride are to be dissolved in about 500 cc of hot water and the solution then allowed to cool, even though crystals of the salt separate. Twenty-nine grams of potassium hydrate are next dissolved in about 300 cc of water: 15-20 cc of acetone should now be placed in a capacious glass balloon, and diluted with 250 cc of water. The reaction is then to be managed as follows: ’about 150 cc of the alkaline solution should be added to the aqueous acetone, and then 250 cc of the mercuric chloride poured in. Resolution of the mercuric oxide first thrown down proceeds slowly a t the outset, if the mixture be not warmed. After a time the oxide redissolves quickly, if the contents of the balloon are agitated briskly. When the first half of the mercuric solution has been added, the remaining 150 cc of potassium hydrate are to be poured in cautiously and the residual mercuric chloride then mixed, with the precautions already stated. “ The solution prepared in the manner described is usually turbid, but can easily be filtered clear from the small amount of mechanically suspended matter. The filtrate should next be placed on a large hoop dialyzer, covered as usual with care‘‘Liquid Diffusion Applied t o Analysis,” Phil. Trans.,
151, 183
(1861).
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fully prepared parchment-paper, and the vessel floated on a considerable volume of distilled water. After two days action the diffusate will be found to contain a large quantity of potassium chloride, some potassium hydrate and but a very small amount of mercury. The process of diffusion is to be continued, the diffusate being replaced by pure water twice each day, until the liquid on which the analyzer floats no longer affords a cloud when treated with a solution of silver nitrate. The process may then be considered terminated, and the pure colloidal liquid obtained. The contents of the dialyzer can now be removed, and should be free from all odor of acetone. A few drops, when evaporated to dryness on platinum-foil and the residue ignited, should volatilize completely. “The mode of operating just described affords the strongest colloidal liquid that can conveniently be prepared directly in the pure state; but where degree of concentration is of no importance, I find that it is better to dilute the alkaline mercurial solution with its own volume of pure water just before dialyzing.” Reynolds evaporated the carefully prepared colloid liquid to dryness; the resinoid residue was powdered very finely and dried carefully. The composition of the substance could be represented satisfactorily by the formula (CH3COCH3)2Hg303and Reynolds assumed that the substance was a definite chemical compound. While this may be true, the evidence would not nowadays be considered as conclusive. Reynolds has the following to. say in regard to the properties of the alleged compound: “Analogy would lead us to conclude that the colloid liquid obtained by dialysis is a hydrate of the body represented by the above formula ((CH3COCH3)2Hg303); but since evaporation i n zluc.uo is sufficient to remove the water completely, the hydrate can possess but little stability. Properly speaking, this hydrate is no doubt a true liquid, and as such is miscible with other liquids. The reaction of this hydrate is neutral to test-papers.
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“ When the aceto-mercuric hydrate contains five percent of the anhydrous compound, it will, if quite pure, remain liquid for twelve or fourteen days, toward the end of this time becoming gradually less fluid, until the whole ‘sets’ to a firm jelly. The same result may be brought about in a few seconds by the addition to the perfectly neutral liquid of very minute quantities of any of the following substances : hydrochloric, acetic, nitric, sulphuric (incompletely), chromic, oxalic, tartaric, or citric acids; by potassium, sodium, ammonium, barium and calcium hydrates ; by calcium chloride, mercuric chloride, sodium acetate, and other neutral salts. Contact with certain insoluble powders’, such as calcium carbonate, and even alumina, induces pectization. “ Elevation of temperature quickly determines the gelatination of the liquid. If containing five percent of the ketone compound, a very firm jelly is produced on heating to 50’ C. In one experiment, a quantity of the liquid was taken and some bright, carefully-cleaned copper gauze introduced. The liquid did not pectize, nor did any trace of mercury deposit on the copper, after standing for a day. The temperature of the whole was then raised to 50’ C.; a transparent jelly was at once produced, of such strength that the vessel in which it was contained could be inverted without any risk of loss. This jelly, enclosing the bright copper gauze, has remained in my possession for eight months without giving the slightest indications of a disposition to change. “ Small zoological specimens, when inclosed in the same. way in a jelly of the mercuric ketone compound, were found to keep well when carefully cleansed before they were sealed up in the gelatinous envelope. “ B y evaporation, a liquid containing eight percent of the ketone compound was obtained, but i t pectized in a few hours.
I n accordance with the nomenclature of Professor Graham, we must call the liquid colloid hydrate the “hydrosol” of the new compound, the gelatinous hydrate the “hydrogel” and the change from the former t o the latter “pectization.”
,
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A two percent hydrate retained its liquidity for several months. Once a jelly formed in any of these liquids, I have not succeeded completely in reconverting it to the liquid state by very cautious treatment with potassium hydrate, even when aided by diffusion. “The alcosol of the mercuric ketone compound was obtained by the method adopted by Professor Graham in preparing the corresponding silicic alcoholate-that is to say, by adding to a one percent hydrate an equal volume of alcohol, and exposing the mixture over quicklime until most of the water was removed: the alcohol remained. This liquid could be boiled without pectizing; but if the ebullition continued for some time, a jelly was suddenly obtained. This insoluble jelly corresponded t o that produced on heating the hydrate, or adding to i t any of the bodies capable of pectizing it; in the former case alcohol, and in the latter water, being associated or united with the mercuric ketone compound. “ I t has now been shown that the new body is capable of affording hydrosol and hydrogel, and alcosol and alcogel; it must, therefore, be regarded as a very strongly marked member of Professor Graham’s group of these colloids, though chemically differing widely from previously described compounds of this class. “When the colloid hydrate was treated with sulphuretted hydrogen, mercuric sulphide was produced. The liquid filtered from the sulphide yielded acetone on distillation. Digestion with dilute hydrochloric acid likewise effected the decomposition of the colloid body, mercuric chloride being produced and acetone liberated. Nitric and sulphuric acids, when dilute, did not decompose the compound with the same facility as hydrochloric acid. Treatment of the hydrosol with copper, zinc, or iron at ordinary temperatures, failed to effect the substitution of either metal for the mercury in the compound. Prolonged contact with each of the two last-mentioned metals caused pectization, the metal subsequently becoming encrusted with a white substance. Heat produced the same result more rapidly.”
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A t first I repeated Reynolds’ experiments exactly but I soon found that the process could be simplified if one was interested chiefly in making a jelly. The easiest method is to dissolve 30 grams KOH and 2 0 cc acetone in 500 cc water and to add slowly a saturated solution of mercuric chloride, shaking the mixture continually until the first faint, permanent precipitate appears. A precipitate appears on adding the mercuric chloride but disappears on shaking until a certain amount of mercuric chloride has been added, after which either a white flocculent or a fine, yellow, granular precipitate is formed. The solution jells on standing exposed to the air for a length of time depending on the concentration of the mercuric chloride. The solution may also be made to jell by desiccation over sulphuric acid, by addition of a small amount of an acid, or by heating; but too much heating causes the precipitation of a fine granular precipitate and the solution then does not jell. It is important to use a sample of mercuric chloride containing no mercurous chloride. Since mercurous chloride is by no means an unknown impurity in this case, it is much wiser to recrystallize the mercuric chloride from water. The first experiments concerned the variation in the amount of mercuric chloride. To each beaker were added 40 cc KOH and acetone solution, and then a definite amount of a saturated solution of mercuric chloride. The beakers were allowed to stand for three days and were then examined. The beakers containing 1-15 cc mercuric chloride solution did not jell a t all. There was a black precipitate in the bottom of each beaker and a clear, yellowish.liquid above. With 2 0 cc HgClz solution, the solution becomes opalescent and there is a heavy granular precipitate. With 30 cc HgClz solution there is formed a soft jelly with a thin layer of liquid on top. With 50 cc the solution jelled after standing several hours; at first there was a thin layer of liquid on top of the jelly but this disappeared in time. With 60-90 cc mercuric chloride solution a firm jelly was obtained in a short time. With
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IOO cc HgClz a jelly is formed with a permanent supernatant liquid layer. It is thus clear that a good jelly is obtained only between certain limits for the mercuric chloride. If left standing for a long time, these jellies dry out and contract, shrinking away from the glass walls of the beaker and cracking. They still remain moist for a long time; but finally dry down to little heaps of powder. The jellies are a pure white color and feel like salve when rubbed between the fingers. They are alkaline to litmus paper. One sample of jelly was sealed in an air-tight dish t o prevent loss of moisture. At the end of three months the jelly was apparently entirely unchanged. In another run I made up mixtures containing 40 cc KOH and acetone solution and 50 cc saturated HgClz solution. To these were added two-gram lots of different salts. With potassium sulphate, and sodium nitrate, no immediate effect could be noticed, the solutions apparently giving as good . jellies as though the salts had not been added. Of course, the salts crystallized in case the jellies were left standing a long time in the air. With sodium acetate a jelly-like structure was obtained; but no real jelly. Addition of potassium carbonate gave rise to a thick, viscous, milky liquid while addition of cobalt sulphate or copper nitrate caused the formation of a granular precipitate. In the next set of runs So cc HgCla solution were added to 40 cc KOH and acetone solution. The mixtures were heated for varying times and consequently to varying temperatures, so as to bring out the effect of heating. The ordinary temperature was 20'. When not treated at all, the mixture was an amber-colored solution which formed a good jelly on standing. When the solution was heated for one minute (to 30') it jelled more rapidly than the unheated solution. On heating two minutes (to 39'), the solution became cloudy, then separating into a good jelly a t the bottom and a yellow liquid above. In time the solution dried to a firm jelly with no upper liquid layer. The same thing happened when the solution was heated three minutes (to 60°),
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or four minutes (to 63 "). When heated five minutes (to 69 ") a white, cloudy precipitate formed which became granular and settled to the bottom. Though a jelly was formed, i t was not a good one. When the solution was heated longer, a granular precipitate settled and no jelly was formed. It is not solely a question of evaporation because one mixture was placed in a flask fitted with a reflux condenser and was boiled for eight hours. A granular precipitate settled and no jelly was formed. If the mixture is placed in a stoppered bottle a t room temperature, a jelly is formed with a liquid layer on top, showing that evaporation is necessary in order to get a firm homogeneous jelly when starting with these solutions. If time had permitted I should have liked to try varying the relative amounts of caustic potash and acetone, and the absolute amounts of water. The jellies do not dissolve in water even though the water be boiled for several hours. They break down, however, into a granular precipitate. If a few drops of concentrated hydrochloric acid or nitric acid be added to the water, the jellies dissolve readily to a clear solution when heated. If this solution is cooled and then made alkaline either with KOH or with the KOH and acetone solution, no jelly is obtained and the precipitate contains a good deal of black mercurous oxide. I did not have time to find out when or how the reduction to mercurous salt took place. Since it has seemed impossible to get a jelly when the mercuric chloride contains mercurous salt originally, it is possible, though not proved, that the mercuric oxide jellies could be made to liquefy and to jell alternately for an indefinite number of times if no reduction to mercurous salt took place. The general results of this paper are: I . Reynolds' work on mercuric oxide jellies in presence of acetone has been repeated and confirmed. 2 . For given amounts of acetone and caustic potash,, the amounts of mercuric chloride can vary only between limits if a good jelly is to be obtained.
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3. Addition of potassium sulphate or of sodium nitrate had no apparent effect on the jelling of the mixture; addition of potassium carbonate caused the formation of a viscous milky liquid, while cobalt sulphate or copper nitrate caused the formation of a granular precipitate. 4. A slight rise in temperature causes a mixture to jell more quickly; but heating for five minutes or more a t temperatures above 63' seems to prevent the formation of jellies. 5. The effect of heating is primarily a temperature phenomenon and not one of evaporation, for the formation of a jelly is prevented by heating the mixture in a flask fitted with a reflux condenser. 6. When heated with water the mercuric oxide jellies break down to a granular precipitate. 7. When the jellies are heated with water to which a few drops of concentrated hydrochloric acid or nitric acid have been added, no jelly is formed; but we get a granular, black precipitate, which contains mercurous oxide. No jelly is formed when the solution is made alkaline again. 8. It is not known whether it is the mercurous oxide which alone keeps the solution from jelling a second time. 9. The mercuric oxide jellies break away from the glass walls when drying. They also crack, but no second layer of liquid forms . This investigation was suggested by Professor Bancroft and has been carried out under his supervision. Cornell University June, I 913
