solved. If we saturate the solution with sulphurous acid, and treat the precipitate again with ammonia, the chloruret of silver will be alone dissolved.

On digesting in iodic acid oxide of zinc recently precipitated and well washed, I obtained a pulverulent salt, but little soluble in water, which deflagrates on burning coals, but much more feebly than iodate of potash. We may obtain the same salt by mixing a solution of sulphate of zinc with that of a soluble iodate. No precipitate appears at first; but after some hours, small crystals are deposited, sometimes in grains perfectly spherical, which are iodate of zinc. It is necessary for success in this experiment that the sulphate should not be very much concentrated, for its viscosity would oppose the motions of the molecules, and of course the formation and separation of the iodate of zinc.

The solutions of lead, of pronitrate of mercury, of pernitrate of iron, of bismuth, and copper, give with the iodate of potash white precipitates soluble in acids. The solutions of peroxide of mercury and of manganese were not altered.

There do not exist any iodureted iodates; at least I have not been able to form them. Iodates and iodic acid do not dissolve more iodine than water.

To complete the history of the saline combinations of iodine, it remains to be determined whether, when a base acts upon this substance in water, the two salts which may be obtained exist separately in the solution, or if they are formed at the instant that any cause whatever determines their separation.

If we mix together the neutral solutions of iodate and hydriodate of potash, they do not mutually decompose each other; but if we add any acid whatever to the mixture, even carbonic acid, which is driven from all its combinations by hydriodic acid and iodic acid, iodine is precipitated, owing to the mutual decomposition of the two salts.

To render the solution of iodate and hydriodate entirely the same with that which we obtain in making iodine, potash, and water, act upon each other, and which is always alkaline, it is sufficient to add to the former the quantity of potash necessary to bring it to the same degree of alkalinity. In that case we can no longer distinguish the one from the other. It would appear, then, that the iodate and hydriodate of potash are formed at the instant that the iodine acts on the alkali in water; but that the oxygen of the iodic acid and the hydrogen of the hydriodic acid preserve a great tendency to combine together, and that it is sufficient to favour this tendency in order to cause it to take effect. Iodic and hydriodic acids, and in general all acids produced at once by the two elements of water, destroy each other when mixed together.* This is the

M. Berthollet has observed that sulphurous acid and hydro-sulphuric acid may exist together when dissolved in a great deal of water. The same thing holds with the two acids of iodine, which if concentrated give a copious precipitate of iodine as soon as mixed, but do not decompose each other when diluted.

reason why a very weak acid precipitates iodine from a mixture of iodate and hydriodate; for how weak soever its action should be, it will always decompose a small portion of each salt, as Berthollet has shown, and the acids separated producing immediately iodine which precipitates, the decomposition may continue, and make great progress, without, however, becoming complete.

The solution of neutral iodate and hydriodate, and the solution of iodine in potash, present, however, this remarkable difference, that the first always preserves its neutral state, while the second is constantly alkaline; but if the two salts be really formed at the instant iodine is mixed with solution of potash, it would appear that we ought either to obtain a complete saturation of the alkali, or that the mixture of neutral iodate and hydriodate ought to become alkaline as soon as it is made. The reason why this is not the case is, that we cannot suppose that in a mixture of various bodies each element acts rigorously, as if it were merely mixed, and as if the mobility of its particles were perfect. We ought rather to admit, that to destroy a compound stronger forces are necessary than those that formed it. On this supposition it is easy to conceive that the alkalinity of the solution of iodine in potash, and the constant neutrality of a mixture of neutral iodate and hydriodate, may take place at the same time; and of consequence, that the two salts of which we have been speaking may be formed, and exist separately, in a solution of iodine and potash.

Hydriodic Ether.

I have paid but little attention to the action of iodine on animal and vegetable substances; yet it may produce several new combinations. MM. Colin and Gaultier have described that which iodine forms with starch; and I shall now make known an ether formed by hydriodic acid and alcohol.

I mixed together two parts in volume of absolute alcohol and coloured hydriodic acid of the specific gravity 1.700. I then distilled the mixture in a water-bath. I obtained an alcoholic liquid, perfectly neutral, colourless, and limpid, which, when mixed with water, became muddy, and let fall in small globules a liquid at first milky, but which gradually became transparent. This liquid is hydriodic ether. What remained in the retort was very dark coloured hydriodic acid. Thus in this experiment a portion of the alcohol had united with the hydriodic acid, and formed an ether, which distilled over with the rest of the alcohol, and there remained hydriodic acid very dark coloured, because it held in solution all the iodine which had coloured it at first. It was probably the action of the iodine and the water which prevented the whole hydriodic acid. from combining with the alcohol.

Hydriodic ether, after having been washed two or three times with water, in which it is but very little soluble, is perfectly neutral. Its odour is strong, and, though peculiar, is analogous to that of the other ethers. After some days it acquires a red colour, which does

not afterwards increase in intensity. Potash and mercury destroy this colour on the spot by uniting with the iodine to which it is owing. Its specific gravity at 72.5° is 1-9206. It boils (as determined by its tension) at 148.6°. By direct experiment, I found it to boil at 148.1°. It is not inflammable; it exhales only purple vapours when thrown upon burning coals. Potassium may be preserved in it without alteration. Potash produces no immediate alteration on it. The same is the case with nitric and sulphurous acids and chlorine. Concentric sulphuric acid renders it speedily brown. When passed through a red-hot tube, it is decomposed. I obtained an inflammable carbureted gas, very brown hydriodic acid, and a little charcoal. Besides these products, I obtained, by putting a solution of potash into the tube in which I produced the decomposition, a substance in fucks which refused to dissolve in the alkali and in acids. This substance, after being several times washed in cold water, preserved an ethereal odour, but not so strong as that of the liquid ether. In boiling water the flocks united together, and melted into a matter, which, after being cooled, resembled white wax in appearance. When put upon a burning coal, it gave out without flaming vapour of iodine in greater abundance than the hydriodic ether. It volatilizes, but much more slowly than the ether.

From these properties I consider the substance of which I have been just speaking as a peculiar ether, formed without doubt by the combination of hydriodic acid with a vegetable matter different from alcohol. I have not analyzed hydriodic ether; but on comparing it with hydro-chloric ether, which, according to Thenard, is composed of a volume of hydro-chloric gas and half a volume of pure alcoholic vapour, I consider its composition as analogous. According to this hypothesis, hydriodic ether is composed in volume of Hydriodic gas Alcoholic vapour

or in weight, of

Acid

Alcohol

and hydro-chloric ether, of

Acid

Alcohol

0.5

100

18.35

100

64.67

Supposing this composition correct, it is astonishing that hydri odic ether is not inflammable, while hydro-chloric ether possesses that property in a great degree. We cannot suppose that this difference depends on the proportions in weight of the acids to alcohol. I rather think that hydriodic ether is not inflammable, because its acid is decomposed by oxygen without producing flame, and hence the oxygen becomes too small in quantity to support the combustion of the alcohol. It would be easy to verify this conjecture by burning

the ether in oxygen gas; for if it is well founded, the combustion in this gas should be attended with flame.

On calling to mind the different experiments in this memoir, we shall see that there is not one which authorizes us to consider iodine as a compound body, or as a substance containing oxygen. On the contrary, we must be struck with the resemblance which it bears in some cases to sulphur, and in others to chlorine. Like them, it forms two acids, one by combining with oxygen, the other by combining with hydrogen: and we may have remarked that the acids formed at once by the combination of chlorine, iodine, and sulphur, with the elements of water, present this remarkable property, that when the acid formed by oxygen has its elements very condensed, that formed by hydrogen has them very weakly united.

Thus sulphur takes oxygen from iodine, and iodine takes it from chlorine; but, on the other hand, chlorine takes hydrogen from iodine, and iodine from sulphur.

If we follow this analogy still further, we find that it holds likewise with respect to carbon; for sulphur deprives it of hydrogen, but yields to it oxygen. Thus it would appear that the more a body condenses oxygen, the less it condenses bydrogen.* This is, without doubt, a cause why the very oxidable metals, as iron, manganese, &c. do not dissolve in hydrogen. I say one of the causes; for if it were the only one, we could not see how mercury, silver, and gold, do not combine with hydrogen, though they have a very weak affinity for oxygen.†

The other analogies which iodine has with sulphur and chlorine are very numerous. Some iodates resemble the chlorates exactly; but most of them have a greater analogy with the sulphates. The iodurets, sulphurets, and chlorurets, in general exhibit the same phenomena with water; and the action of sulphur, iodine, and chlorine, upon the oxides, with or without water, is exactly similar. In short, all the properties of iodine may be classed between those of sulphur and chlorine. It is not necessary to remark, that though

From these considerations I do not hesitate to class azote with oxygen, jodine, chlorine, and sulphur. Nitric acid has a considerable resemblance to iodic acid and chloric acid by the property which it has of being easily decomposed; and because azote takes, like chlorine and iodine, two and a half times its volume of oxygen. The nitrates are decomposed by the fire, like the iodates. But we do not know any oxide from which azote disengages oxygen, from which we can conclude only that it has much less energy than this last body. Azote forms likewise with chlorine and icdine combinations which are easily decomposed, which shows that it has little affinity for them, and that it approaches them by the nature of its energy. If it does not form an acid with hydrogen, this is doubtless because in ammonia there are three volumes of hydrogen for one of azote; and in all probability, in order to produce an acid, only equal volumes are requisite. The acid combination of azote and hydrogen appears to me realized in prussic acid, which, from some experiments that I have made, and shall soon publish, I am induced to consider as an acid analogous to the combinations of chlorine, iodine, and sulphur, with hydrogen; only that its radicle is a compound of azote and carbon. Oxygenated prussic acid corresponds to chloric and iodic acids.

+ See note B at the end of this memoir.

I have restricted myself to compare iodine with sulphur and chlorine, we might find analogies, though less numerous indeed, between it and phosphorus, and several other bodies; but I thought it better to compare it only with those bodies to which it bears the greatest resemblance, and among which I conceive it ought to be classed. I have been led by this to show that sulphur possesses all the general properties of chlorine, and that we ought in consequence to place it among those bodies which form acids by combining with hydrogen. (To be continued.)

ARTICLE II.

Analysis of the Excrements of the Boa Constrictor. By Dr. Prout.

THE substance sent me as the excrements of the boa constrictor was solid, of a white colour inclining to yellow. Fracture earthy. When rubbed on a hard surface it left a white mark like chalk. Its feel, however, was rather more dry and harsh than that of chalk, and it was more friable than that substance. Smell faint and mawkish. Sp. gr. 1385.

I.-A. After making a few general experiments to ascertain its nature and composition, 50 grains, well dried and in a state of fine powder, were digested for 24 hours in dilute muriatic acid; the mixture being occasionally, during that time, gently heated and well shaken. On adding the muriatic acid no effervescence was perceived. The acid was then poured off, and in order to remove the whole of it, the substance was repeatedly well washed with distilled water, which washings were added to the acid. It was now carefully dried and weighed, and was found to have lost 4.92 grs., which, of course, were taken up by the muriatic acid, and remained in solution in it.

B. On the substance which had been left undissolved by the acid, and which had become of a bluish tinge, a solution of pure potash was poured, which, on the application of heat, completely dissolved it, forming a solution transparent and nearly colourless. To this solution, while still warm, was added muriatic acid in excess, which occasioned a copious white precipitate in the state of very minute but distinct grains, which, after having been well washed, was collected and dried. The following were its properties. It existed, as before stated, under the form of very minute grains of a beautiful bluish white pearly appearance. No smell. Nearly insipid. Very sparingly soluble in cold water; but rather more soluble in warm, and its solution faintly reddened litInsoluble in alcohol. It combined with all the alkalies, earths, &c., forming compounds very little soluble in water. When nitric acid was poured upon it and heat applied, it was en

mus.