WITH SOME OBSERVATIONS ON THE SAME BODIES CONSIDERED IN THE AMORPHOUS AND CRYSTALLINE STATES.*

BY M. J. PELOUZE.

IN repeating some of the principal experiments which M. Gay-Lussac has made known in his Memoir "On the Combinations of Chlorine with Bases," (for which see THE CHEMIST, Vol. III. pp. 294, 336, 374), I

have observed that the action of chlorine on red oxide of mercury, is not uniform, and that it is considerably modified by the mode in which that oxide is prepared. I have endeavored to account for this circumstance,

which appeared to me singular, and it is thus that I have been led to occupy myself with the work which I now have the honor of presenting to the Academy.

Oxide of mercury prepared by decomposing with an excess of potassa the nitrate or the bichloride of mercury, washed and dried at the ordinary temperature, projected into a flask completely filled with dry chlorine, gives rise to a vivid disengagement of heat and light. Numerous crystals of bichloride of mercury fill the capacity of the flask and are very soon condensed on its sides. The greenish-yellow color of the gas disappears; it gives place to a pure but faint orange yellow color. If the cooled vessel be opened in water, it rushes into it, and occupies the chief portion of it; but an insoluble residue, consisting of free oxygen, is constantly observed. The volume of the latter gas varies with the quantity of chlorine operated on, with the temperature, and with the state of division of the oxide. If, instead of putting the oxide of mercury in contact with the chlorine, at the ordinary temperature, this gas be previously cooled by plunging the flask which contains it into a refrigerant mixture, the light, which is the sign of energetic chemical action, ceases to show itself, the temperature of the mixture rises but

Comptes Rendus, No. 2, Jan. 9, 1843. N.S. VOL. I.-No. VI, June, 1813.

Finally, when the tube is surrounded with ice, however rapid the current of chlorine which passes through it, hypochlorous acid is still produced.

In a word, the only gaseous product which results from the action of chlorine on oxide of mercury is hypochlorous acid, when the operation is performed in such a manner that no elevation of temperature can take place.

After a certain lapse of time, the oxide of mercury which is still incompletely decomposed, and whose temperature is considerably raised by its contact with a rapid current of chlorine, acquires the property of

giving almost pure hypochlorous acid by the subsequent action of this gas.

This result suggested to me the idea of immediately employing in the preparation of hypochlorous acid the oxide of mercury obtained by precipitation, and calcined at a temperature of 300 or 400° C. Indeed, such oxide, introduced into a flask filled with chlorine, gives rise to a gas of a pure orange-yellow color, which is very pure hypochlorous acid. The action is less rapid than with the oxide dried at a low temperature; it requires some minutes to entirely accomplish it. The water in which the flask is uncorked, rushes into it and fills it without any perceptible residue.

On the other hand, as might be expected, if chlorine be passed through a tube filled with the same oxide, pure hypochlorous acid is still obtained, or only mixed with chlorine, when the current of this gas has been too rapid.

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It may be conceived how important are the above-mentioned results in the preparation of hypochlorous acid.

The process for obtaining this acid, which M. Balard has published, is very complicated and difficult of execution. It has been very beneficially simplified by M. Gay-Lussac, who has proposed to prepare dry hypochlorous acid gas directly with chlorine and oxide of mercury, in the absence of all moisture. This means perfectly succeeds when the oxide has been previously calcined: but a volume of chlorine, in re-acting, in a close vessel, on oxide of mercury, can produce only half of its own volume of hypochlorous acid gas, these two gases being supposed at the same temperature. This fact, so important for the history of hypochlorous acid, has been put beyond doubt by several very curious experiments made in this respect by M. Gay-Lussac himself. It follows, therefore, that as soon as the flask, in which the hypochlorous acid has been prepared, is opened, this gas is mixed with its own volume of atmospheric air.

Independently of this principal cause of impurity, the gas is in contact with chloride and oxide of mercury, or with oxychloride of that metal.

All these inconveniences will be avoided by preparing it in the same manner as other gases soluble in water, and decomposable by mercury. The following is the process which I propose for that purpose:

Chlorine is driven, bubble by bubble, into a flask of water in order to wash it, and thence into two tubes, the first of which is filled with chloride of calcium to dry it, and the other with binoxide of mercury, precipitated and calcined at a temperature near that at which it decomposes. The latter tube is soldered to another of narrower bore, whose extremity dips into the flask which it is desired to fill with hypochlorous acid. The air is expelled from it by the latter gas.

I have tried to liquefy hypochlorous acid gas, and I effected it by submitting it to a cold of -20° C, under the ordinary atmospheric pressure. For this it is sufficient that the tube into which the hypochlorous acid passes should dip into a small glass matrass, with a long neck, surrounded by a mixture of ice and salt. In one or two hours, several grammes of liquid hypochlorous acid may easily be obtained.

The following are the properties of this body:

Its color is red, and quite similar to that of arterial blood; its odor resembles those of chlorine and iodine, but it is stronger, more penetrating, and it more painfully affects the eyes. It enters into ebullition between 19° and 20° below zero. Its vapor is of a reddish

yellow, which it is impossible to confound with the vapor of chlorine, especially when these two gases are compared.

It provokes coughing, and spitting of blood; and it acts, without doubt, as a very violent poison, even in very small doses.

Hypochlorous acid is denser than water; it remains at the bottom of that liquid, in which it gradually dissolves, communicating to it an orange-yellow color.

Arsenic, phosphorus and potassium burn with flame and often with violent explosion, when thrown into liquid or gaseous hypochlorous acid.

Antimony in powder acts in the same manner; but when it is employed in a not very divided state, for example, in small shining pieces of the size of a pin's head, liquid hypochlorous acid may be distilled over this metal without any alteration of these two bodies being remarked.

When we reflect, on the one hand, on the excessive instability of hypochlorous acid, and, on the other hand, on the violent action exerted on it by powdered antimony, it appears to me that we cannot but compare the above phenomena with those presented by spongy platinum and the same metal fused, in their contact with a mixture of hy. drogen and oxygen. It would suffice, in this hypothesis, to pulverise antimony, to bring it to a state corresponding to that of spongy platinum.

Hypochlorous acid detonates under the influence of a gentle heat, but sometimes its elements separate slowly and without noise. A remarkable thing is that the vibrations caused by a single stroke of the file on a tube, at the bottom of which a few drops of hypochlorous acid have been condensed, are sufficient to cause this acid to detonate, even at a temperature of -20° C. It is also very dangerous to pour it from one vessel into another.

I at first thought that the red liquid of which I have been speaking was a compound of one equivalent of chlorine with two equivalents of oxygen; but, in the first place, the mode of preparation which I followed to obtain it, and, in the second place, the products of its decomposition by heat, which consist of two volumes of chlorine to one volume of oxygen, and the comparative examination of the properties of the aqueous solution, with that prepared by the process of M. Gay-Lussac and M. Balard, left me in no doubt as to the identity of this liquid with hypochlorous acid; only this acid was hitherto known only in the gaseous state, and the preceding experiments show that it can be liquefied, at the ordinary pressure, by a cold of some degrees below zero C.

I have already said that hypochlorous acid is really colored, whether in the gaseous or liquid state, or in more or less concentrated aqueous solution.

This is demonstrated by the following facts:

Hypochlorous acid liquefied by cold, put in contact with water, at a low temperature, is gradually dissolved in it, retaining to the end its orange-yellow color. These fractioned solutions all present an orange-yellow color.

The water in which the hypochlorous acid gas is directly received does not appear to be colored in the commencement of the operation, but its tint becomes deeper as the solution progresses; and that happens, whatever care may be taken to preserve uniformity in all the conditions of the experiment.

This solution, agitated with binoxide of mercury, is not decolored, which would appear to indicate that no free chlorine is present, for the latter would act on the oxide, and give rise to a fresh quantity of hypochlorous acid.

When oxide of mercury is mixed with water at 2° or 3° C., holding in suspension a great quantity of crystals of hydrate of chlorine, the latter disappear, producing hypochlorous acid, and the liquor left for a few moments to itself in order to separate it from the excess of oxide, presents a deep yellow tint. I have in this manner several times obtained a colored liquor which did not contain more than eight or ten times its volume of hypochlorous acid. The low temperature at which this experiment was made does not seem to authorise the explanation which would consist in referring the coloration of the liquor to free chlorine.

The chlorine which is passed into cold water holding in suspension oxide of mercury, likewise gives a colored solution of hypochlorous acid.

Concentrated solutions of hypochlorous acid, submitted to the action of a gentle heat, disengage a reddish yellow gas.

All the above facts appear to me capable of being easily explained, and in the following manner :

Hypochlorous acid is a gas of a reddish yellow color. This color is proper to it; it preserves it so long as it is gaseous and free from water it is rendered deeper by liquefaction.

This acid forms with water a hydrate of an incomparably less intense orange-yellow color than that of the gas, so that when the solution is slightly charged, it does not appear perceptibly colored, although in reality it is always so. Thus, water which contains several times its volume of hypo

chlorous acid, appears almost colorless when looked at in an ordinary glass; but if it be introduced into a narrow glass tube of 2 or 3 decimetres in length, it will be found to have a very distinct yellow tint; and this occurs just as well with the aqueous solution of the hypochlorous acid prepared by the process of M. Balard or M. GayLussac, as with that made with the liquid acid.

It seems to me, therefore, that hypochlorous acid, like the other gases formed by the combination of chlorine with oxygen, is really colored, and if it did not appear such to M. Gay-Lussac, it is probably owing to his having studied only weak solutions. These solutions, indeed, appear very perceptibly colored, only when they are charged with a very considerable quantity of gas; and as regards this latter, under the pressure of 0.38, at which M. Gay-Lussac had obtained it, it likewise appears clearly colored, only when a very great volume is regarded.

Hypochlorous acid is much more soluble in water than had been supposed. The latter dissolves, at zero, at least 200 times its volume. Indeed, 1 cubic centimetre of this solution destroyed 400 cubic centimetres of normal arsenious liquor. The chlorine and the oxygen having an exactly equal decoloring power in hypochlorous acid, as M. GayLussac has demonstrated, and the formula Cl O, representing 2 volumes of this gas, it follows that water dissolves 200 times its volume of it. In other terms, 1 volume of this solution decolors as much as 400 volumes of chlorine. It marks, consequently, 40,000 chlorometric degrees.

The density of hypochlorous gas being 2.977, 1 litre of this gas, at zero and at 0.760, weighs 35-864: 100 parts of water should therefore dissolve 77:364 of hypochlorous acid, or more than three fourths of its weight. These proportions nearly correspond to 1 eq. of acid and eq. of water.

The aqueous solution of hypochlorous acid has been carefully examined by M. Balard; but he had not obtained it in nearly so high a degree of concentration: I will point out some of its properties.

Its color is yellow, like that of a concentrated solution of chloride of gold; its odor is penetrating and insupportable: it is the same as that of the decoloring chlorides, except in its intensity, which is much greater. It has a very caustic action on the skin, which it rapidly disorganises and destroys, producing violent pain and a deep wound, which cicatrises only with difficulty.

Antimony rapidly decomposes it; arsenic inflames in it, producing in the midst

of the liquid a beautiful blue color. Hydrochloric acid, ammonia and oxalic acid produce in it brisk effervescence: arsenious acid acidifies in it, giving rise to slight detonations.

It causes the sulphuret of lead immediately to pass to the state of sulphate, and this property is so powerful, that it exists to a high degree in a solution diluted with 200 times its volume of water. It may be turned to account for bleaching wainscots and pictures, on the surface of which ceruse has been blackened by sulphurous emanations.

The aqueous solution of hypochlorous acid produces in the salts of protoxide of manganese, a black, velvety, precipitate of pure hydrated peroxide of manganese.

In the salts of lead, it forms a precipitate of puce oxide.

Hypochlorous acid may easily be turned to account for obtaining the two preceding oxides in a state of division, which renders them proper for some particular reactions. Of the different salts of lead, that which appears best fitted for the preparation of puce oxide, is the tribasic acetate dissolved in a large quantity of the water.

As M. Balard observed, hypochlorous acid may be placed beside oxygenous water, from the facility with which its elements disassociate under the influence of certain bodies, which besides neither yield to it nor take from it anything. Thus it is that the chloride of silver rapidly decomposes its aqueous solution.

The easy decomposition of this acid by hydrochloric acid furnishes an excellent means of procuring in abundance crystals of hydrate of chlorine. It is sufficient to cool to +2° C. or 3° C. a solution of hypochlorous acid, and pour into it, drop by drop, hydrochloric acid. The chlorine eliminated unites with the water, and there results from it so large a quantity of crystals, that the liquid is almost entirely solidified.

I have pointed out the conditions to be fulfilled to obtain an oxide proper for the preparation of hypochlorous acid. I shall now show how different are the results of the action of chlorine on this oxide, when it is prepared by the calcination of the nitrate or by the direct oxidation of mercury.

The oxide which proceeds from these modes of preparation has a deeper orange color than that of the oxide obtained by the humid way. It is crystallised in more or less voluminous bracteæ, or in microscopic needles, glittering in the sun's light. When this oxide is submitted to the action of chlorine, in conditions similar to those which I have just indicated for the precipitated oxide, no sensible elevation of temperature

is observed; the production of hypochlorous acid is so inconsiderable, that I for a long time thought none at all was formed, and it is only after a contact of several hours that it is possible to detect it. This inertness exists as well with the microscopic crystals as with the voluminous lamellæ. If, by long trituration, this oxide be reduced to an impalpable powder, it will give rather more hypochlorous acid; but, compared with the proportions furnished by precipitated oxide of mercury, these quantities are still infinitely small.

What can be the cause of these differences, which cease to exist in water, whatever may have been the mode of preparing the oxide of mercury? I know not; but I am led to believe that they may be due to two different physical states of this oxide.

The amorphous oxide alone would be susceptible of being decomposed by chlorine at the ordinary or a low temperature; the crystallised oxide would resist in the same circumstances. What leads me to give this opinion is, that the tribasic sulphate of mercury obtained by the prolonged action of boiling water on the neutral sulphate, although prepared by the humid way and dried at a low temperature, does not give hypochlorous acid when put in contact with chlorine, or rather it gives it with extreme slowness and in small quantities, like the oxide of mercury in crystals. Such at least is the manner in which a sample of this mercurial subsalt acted, whose structure appeared crystalline.

The objection which consists in the fact that the crystallised oxide of mercury, and especially its powder, gives with chlorine a small quantity of hypochlorous acid, does not seem to me sufficient to warrant the rejection of the preceding hypothesis, for this oxide might contain the amorphous modifi. cation. I doubt that the chemists who may repeat my experiments may attribute the differences which I have observed to a purely mechanical cause, as a greater number of reacting surfaces in the amorphous oxide. For my part, I should rather believe that pulverisation changes the nature of these surfaces, or sets at liberty small quantities of amorphous oxide concealed in the interior of the crystals.

Be this explanation as it may, I wished to see whether amorphous oxide of mercury and the same oxide crystallised would act in the same manner under the influence of heat.

Recollecting that Wöhler had found considerable differences in the fusing points of the same compounds, according as they were amorphous or crystallised, it appeared