tendency, however, is still to regain its original capacity, so that any substance containing hydrogen, or any other element which combines with the chlorine or iodine, instantly liberates the nitrogen, and it expands with a force equal to that which would be required to liquefy it. *** *

There is but one hydrocarburet of iodine noticed by authors; it appears in colourless acicular crystals, and is formed by the action of olefiant gas on iodine. Faraday, its discoverer, found it, in composition, quite analogous to chloric æther, and called it hydrocarburet of iodine +.

After having thoroughly dried a portion of iodine I introduced it into a flask, which was luted on to a gas tube with sulphate of lime; then the stop-cock was opened, and a constant supply of gas was thus allowed to enter as fast as the former was absorbed. Instantly there is action observed; the small grains of iodine on the sides of the vessel become semifluid, and of a dark colour, and the interior of the flask is gradually filled with ruddy brown fumes. In the course of four hours, the acicular colourless crystals of Faraday began to appear, and that in the shade, showing that the direct rays of the sun are not necessary, as he supposed‡. After the gas had been acting on the iodine for eighteen days I removed the flask, and observed a fluid at the bottom, which when examined was of a blackish green colour. It does not combine with water, but runs into globules like oil, or more exactly like a solution of iodine in creosote when it is placed in water. On the application of the heat of a spirit-lamp to a tube containing this fluid with the mixture of a drop or two of water, slight explosions take place, the black liquid is decomposed, a red fluid rises in vapour, and olefiant gas is evolved. The red fluid is probably a mixture of olefiant gas and free iodine, for it instantly casts with starch the characteristic blue tint.

When the black fluid is put into a small retort, and heat applied, olefiant gas is first driven off, and then a copious effusion of hydriodic acid; whilst at the same time the orange red fluid again appears. When the beak of the retort is placed in water the hydriodic acid is absorbed, and portions of the red and black fuids come over also; the latter falls ot the bottom. The water precipitates starch blue, and the perchloride of mercury instantly causes the precipitation of the periodide of mercury. Alcohol removes the substance that keeps this compound fluid, and the solid green hydrocarburet,

+ See Phil. Trans. for 1821: or Phil. Mag., vol. lix. p. 352.-EDIT. Mr. Faraday certainly formed this compound by exposing iodine and olcfiant gas to the sun's rays, but he does not explicitly represent that the direct rays" are necessary.-EDIT.

to be spoken of immediately, results. The sulphuric and muriatic acids have no action with the dark fluid, whilst they cause the decomposition of the red, precipitating its iodine. There can be little doubt that these two fluids are different compounds, but a limited period prevented any further inquiry.

The next compound to be spoken of is a solid hydrocarburet of iodine, sometimes of a dark blackish colour, at other times, and oftener, of a decided green. It has never been noticed by any chemical author, and differs from Faraday's in the following particulars. His is transparent, in white acicular crystals, shooting out from the sides of the flask, and formed, as I noticed before, in a very few hours after olefiant gas is brought in contact with iodine; of a sweet taste, and aromatic smell: it fuses and sublimes unchanged. Insoluble in water, acids, and alkalies; soluble in æther and alcohol, and may be crystallized from them.

This new hydrocarburet is opake, of a dark green colour, and not of crystalline texture; is formed after a longer action of olefiant gas on iodine; is destitute of taste and smell: it fuses and is decomposed, giving rise to another new compound, hereafter to be noticed; and lastly, is insoluble in both æther and alcohol. Mr. Kemp was the first to discover this compound, but he has never examined its properties. When it is first removed from the flask in which it has been formed, it is mixed with a large portion of Faraday's hydrocarburet, and also with the fluids already noticed: these last are allowed to drip from it, and then on boiling with alcohol the whole of Faraday's hydrocarburet is taken up, and the green compound remains behind, which, after repeated washings with alcohol, may be considered pure. The former sinks in sulphuric acid, whilst the green floats on its surface, and both It burns with a clear flame by are alike unacted on by it. heat; it emits olefiant gas and hydriodic acid, and there remains behind a carbonaceous residue.

At first, from the negative qualities of this green hydrocarburet of iodine, I thought it was merely carbon; but I soon altered my opinion, for I found that by placing this in a small tube retort, I obtained a perfectly new compound by distillation. I was led to this process by observing that when the green hydrocarburet was heated, dense brown fumes escaped, which emitted the odour of garlic. A receiver was therefore adapted to the retort, and being kept cool, a liquid Whenever of a deep reddish brown colour collected in it.

the stopper is removed from the bottle in which it is contained, the room is soon filled with the smell of assafoetida. It is, like the former, highly inflammable, and consists also of

carbon, hydrogen, and iodine. I have not examined its properties further, but from its peculiar odour have called it the foetid hydrocarburet of iodine. ****

The compound of sulphur and iodine formed by GayLussac is most likely merely a mechanical mixture, for after keeping it in alcohol in a closed vessel for several months, the alcohol became saturated with iodine, and the sulphur remained unaltered. I tried to procure a chemical compound in the same way as the chloride of sulphur is formed, but a similar one to the last resulted. I caused hydriodic acid to come in contact with the chloride of sulphur; instant reaction took place, muriatic acid was formed, and a dark compound, which was probably an iodide of sulphur, presented itself. Other means may be had recourse to, as

or, by the action of chloride of iodine on sulphuretted hydrogen, there would result, either muriatic acid and iodide of sulphur, or chloride of sulphur and hydriodic acid.

Having formed the sesquiodide of phosphorus, I laid it aside in a well-stoppered bottle; it, however, in a short time attracted moisture from the air, and on removing the stopper much condensed hydriodic acid burst forth. To get rid of the fumes, I added a small portion of water, and laid it aside; on examining it again I found a yellow powder at the bottom of the fluid. I added now a little more water; but whenever the red powder came in contact with it, instant decomposition took place, and much gas was evolved with brisk effervescence. After the disengagement of the gas had ceased, there still remained a red powder, which being dried and exposed to a moist atmosphere did not attract moisture; therefore it is not any of the former iodides. It bears a considerable heat without change; if, however, it be continued and agitated, it bursts into flame, and burns with the characteristic appearance of phosphorus. It is most probably an oxide of phosphorus, but differs from the following in being darker in colour and much less inflammable. The oxide of phosphorus, which the former resembles, is conveniently formed by placing phosphorus in a long glass tube, and then heating the tube until the phosphorus catches fire and liquefies. A current of air is now made to pass through the tube by blowing forcibly into one end, vivid combustion ensues, and the whole interior of the

tube is filled with the yellow oxide. On raising the tube after the combustion has ceased, from the horizontal to the perpendicular position, a splendid phænomenon takes place; a bright red glow of light commences at the bottom of the tube and gradually rises to the top after traversing the whole mass. This compound Mr. Kemp considers to be an oxide of phosphorus.

I found that when carbon and dry pure boracic acid are heated to redness in a porcelain tube, and pure iodine dropped into it whilst at this high temperature, a small portion of a yellow compound sublimed, which I considered as an iodide of boron.

*

*

When solutions of the protonitrate of mercury and hydriodate of potassa are mixed together, the green protiodide of mercury is precipitated; but by this method a portion of the yellow iodide is almost invariably found mixed along with the green, on account of the presence of a portion of the pernitrate. But this is completely obviated, and a very pure protiodide formed, when the elements themselves are made to act on each other. I found that on agitating together the iodine with an excess of metallic mercury in a tube, that combination was formed. After the action has commenced, the addition of a little water facilitates its completion. This iodide, by the combined influence of air and light, is resolved into metallic mercury and the biniodide. To try which of these agents had the greater power, I placed a portion of the green iodide (being perfectly dry) in a closed box impenetrable by any species of light. On examining it in a few weeks afterwards, I found that it was only partially decomposed, and those portions that had undergone the change had assumed a very beautiful appearance. There was rising out of the mass at different places a formation exactly similar to one of vegetable origin: I. represents a small mass of green iodide from which the cryptogamic-looking excrescence sprung; 2. represents the root, which was of a red

2

crimson colour; and 3. is the upper expanded portion, which on the exterior was covered with a feathery crystallization of the yellow iodide. The interior was hollow, and was externally of the same rich red colour as its root. These vegetations resembled much in richness and beauty the bells of some of the finest heaths.

Another portion of the green iodide was placed in a small phial filled with distilled water, which after being exposed to the light for many weeks, still retained its original green colour, being as yet undecomposed. Air, therefore, is the prinThird Series. Vol. 8. No. 43. Jan. 1836.

D

cipal agent in effecting its decomposition, since in both instances the temperature was the same, and must have affected each alike. As the bichloride of mercury added to a solution of the hydriodate of potassa causes the formation of the biniodide, it might be expected that the protochloride would give us the green protiodide, which on trying I found to be the case; when equal parts of calomel and hydriodate of potassa are added to each other (the one in solution and the other suspended in water) an instant interchange takes place, and the green iodide is produced. This took place in all cases, whether I used the calomel in excess, or vice versa. But I found that on pouring off the supernatant liquid from the green iodide, in either of the above instances, and now adding the calomel, the precipitation wholly consisted of the beautiful bright yellow iodide; or, if to a solution of the nitrate of mercury in excess, there be added the above-mentioned liquid, there is instantly a flocculent precipitation of pure sesquiodide. From these facts I presume that in the process for the production of the green iodide there is formed a sesquichloride of mercury, i. e. a chloride having one half more chlorine in its composition than calomel = (2 Hg + 3 Ch, or 1 Hg + 1 Ch), and analogous to the sesquiodide. I mentioned before that the same results always followed whether I used the calomel, or the hydriodate of potassa in excess.

The yellow sesquiodide of mercury may be kept for any length of time excluded from the light without changing colour; but if exposed it soon acquires a dark hue. By heat one might suppose it had been converted into the biniodide, for it assumes first a red hue, then by continuing the heat it fuses and becomes of a deep crimson colour, and volatilizes into crystals of the same tint, but on cooling the original yellow is restored. It is singular enough that exactly an opposite effect is produced by heat on the biniodide; it is converted at 400° Fahrenheit into a deep blood-red-coloured fluid, which volatilizing condenses on the sides of the tube into yellow acicular crystals, which retain that colour for a considerable time, unless suddenly cooled or agitated, when the characteristic crimson tint of the biniodide again appears.

The biniodide falls as a rich red powder when solutions of the bichloride of mercury and hydriodate of potassa are mixed together, and in this form it is generally seen. I, however, have procured it in pretty large crystalline cubes by the following process. I found that it was dissolved in great abundance by a boiling solution of the hydriodate of zinc. I added the powdered biniodide till no more could be taken up, and