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1815. Wind. Max. Min. Med. Max. Min. Med.

3d Mo.

Mar. 2 Var. 30.22 30.17 30-195 48 35 41.5

Evap. Rain.

8 C

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The observations in each line of the table apply to a period of twenty-four hours, beginning at 9 A. M. on the day indicated in the first column, A dash denotes, that the result is included in the next following observation,

REMARKS.

Third Month.-2. Small rain at intervals. 3. Misty morning: fine day. 4, 5. Cumulostratus. 6. Fine day: Cirri appeared, much elevated, and coloured at sun-set. 7. Fine morning: p. m. cloudy and windy, with some rain: night very stormy. 8. Windy, wet, a. m.: showers by inosculation in the evening. 9. a. m. Hoar frost: turbid sky: rain: p. m. fair. 10. Snow early, after which various modifications of cloud, ending in showers of rain and snow, p. m. 11. Hoar frost: Cirrostratus and Cumulostratus: p.m. Nimbi, with large hail. 12. Dull misty day: at night very stormy, with rain. 13. a. m. Cloudy, with a gale at S. W., and rain at intervals: p.m. several dense Nimbi, thunder, hail, and hard rain: much wind, with distant lightning, at night. 14. Cirrostratus and haze: then Cirri, passing to dense Nimbi: gusts of wind, hail, and rain. 15. The barometer has risen, with an almost uniform motion, about an inch and a quarter in 36 hours; yet the air has not become clear: it should be observed, that there had been much previous depression: a wet forenoon, with a breeze at E.: p.m. Cirrostratus: at night much wind. 16. a. m. High wind at S. W., with Cumulostratus: fair and pleasant. 17. a. m. Much dew: Cirrostratus, with Cirrocumulus: the light clouds after sun-set beautifully tinted with lake and purple. 18. After a few drops, the Cumulostratus prevailed, followed by rain in the night. 19. Some rain, a. m.: then Cumulostratus: and at evening Cirrostratus, with a lunar corona. 20. a.m. Dew: a light veil of Cirrostratus: at evening, the clouds passed to the N. 21. Cumulus, beneath Nimbiform Cirrus, both elevated about five, p. m. during the approach of a squall, the wind was very noisy among the branches (now covered with opening buds), producing an almost vocal modulation of sound: as soon as the trees became wet, this was exchanged for the usual hoarse noise, resembling that of the sea-shore. It is probable that the former effect requires a peculiar sonorous vibration in the branches, the effect of close friction by the air, which the interposition of water does not permit to take place. The night was boisterous. 22. Much wind: showers: two strata of cloud: borne very high, as for some days past. 23. Heavy squalls, with some hail in the showers: p.m. a singular combination of clouds in the E.: it was a Nimbus, with Cumuli adhering and entering at the flanks, while a very lofty columnar Cumulus shot up through the midst of the crown, and this again was capped with a small Cirrostratus. 24. Various clouds: squally, p. m. 25. The same: a brisk evaporation: at sunset, Cumulus at a considerable height, inosculated with Cirrus above, after which two distinct Nimbi in the S., which went away eastward. 26. Driving showers: at evening a lunar corona, followed by much wind and rain at intervals. 27. Stormy: showers. 28. Fair. 29. Large Cirri, which passed chiefly to the Cirrocumulus, p. m. 30. Misty, a. m.: overcast, p. m.: little wind. 31. A very fine day large Cirri formed alone at a considerable elevation, and passed in the evening to the N. W.: much dew followed.

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ANNALS

OF

PHILOSOPHY.

JUNE, 1815.

ARTICLE I.

A Memoir on Iodine. By M. Gay-Lussac.

(Continued from p. 302.)

Hydriodate of Zine.

THIS salt is easily obtained by putting iode into water with an excess of zinc, and favouring their action by heat, as I have already explained. I have frequently attempted, but always without success, to make this salt crystallize, because it is extremely deliquescent. Heat first deprives it of its water, then melts it, and sublimes it in fine prismatic crystals, similar to those obtained when antimony is oxidized. It is not decomposed by this operation, if performed in close vessels; but if air be admitted, iodine is disengaged, and oxide of zinc remains. When this hydriodate is dried, it does not differ from ioduret of zinc.

By taking the mean of three experiments, differing very little from each other, I find that ioduret of zinc is composed of

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Oxide of zinc

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When a solution of hydriodate of potash or soda is mixed with a solution of metallic oxides, no precipitate is obtained with those of manganese, nickel, and cobalt, which proves that the hydriodates of these metals are soluble. Perhaps we may say that all the comVOL. V. N° VI.

2 C

binations of iodine with the metals that decompose water possess

the same property.

On the contrary, the metals that do not decompose water have given me precipitates with the hydriodate of soda. The precipitate of copper is whitish-grey; that of lead, a fine orange-yellow; that of protoxide of mercury, greenish-yellow; that of peroxide of mercury, orange-red; that of silver, white; that of bismuth, chesnut-brown.

I consider all these precipitates as metallic iodurets, and with so much the greater reason, that the hydriodates of the very oxidable metals are changed into iodurets merely by drying them by a gentle heat. Now the force which has determined the insolubility of all these precipitates ought to be considered as much more energetic than a small change of temperature which is sufficient to convert a hydriodate into an ioduret.

It will not be useless, in order to settle our opinions respecting the nature of the combinations of the metals with sulphur, iodine, and chlorine, when in contact with water, to show the analogy which they have to one another.

Among the sulphurets, those only of the metals, which have a much greater affinity for oxygen than hydrogen has, are soluble in water, and may be considered, with some probability, as hydrosulphates. Such are those of potassium, sodium, barium, &c.

Though iron and zinc decompose water, they have not so superior an affinity for oxygen above hydrogen, that the united affinities of the metal for oxygen, and the sulphur for hydrogen, are stronger than that of the oxygen for hydrogen, and the metal for sulphur. I neglect here the affinity of the oxide for hydro-sulphuric acid, because it must be very weak relatively to the others. The metals which readily yield their oxygen to hydrogen will form à fortiori sulphurets, which will not decompose water, and which will bẹ insoluble in that liquid.

When we compare the iodurets with the sulphurets, we must attend to this circumstance, that iodine has a stronger affinity than sulphur for hydrogen, and that from this there ought to result an augmentation of intensity in the forces which tend to decompose water. We see, in fact, that all the metals which give soluble compounds with sulphur form equally soluble ones with iodine; and further, that the iodurets of the metals which decompose water possess the same property. As to the iodurets of the metals, which have less affinity for oxygen than hydrogen, they are insoluble, aș well as their sulphurets.

Pursuing the same comparison with the chlorurets, we ought,

It may be objected, that if the forces which tend to decompose water have increased, because iodine has more affinity than sɗlphur for hydrogen, those which tend to prevent its decomposition have also increased, because iodine has more anity than sulphur for potassium and the other metallic bodies. But we may suppose, with sufficient probability, that the first have increased in a greater ratio than the second.

according to the same principles, to find a greater number which are soluble than of the sulphurets and iodurets, because chlorine has a much stronger affinity for hydrogen than sulphur or iodine. This accordingly is the case. All the chlorurets of the metals which form soluble iodurets are likewise soluble, and besides them those of lead, bismuth, gold, platinum, the deutochlorurets of copper and mercury possess the same property.* We see, then, by the comparison which we have just made, that it is the most oxidable metals, and the radicles that have the greatest affinity for hydrogen, which have the greatest tendency to form combinations soluble in water, and which probably decompose it.

I have attempted to decompose several hydriodates by acids in which the oxygen is very much condensed; but I have not obtained any satisfactory result. The hydriodate of strontian, and that of potash, treated by concentrated phosphoric acid, gave me very deep coloured hydriodic acid. Boracic acid produces no sensible decomposition, because it is too weak as long as there is any water mixed with it, and when there is none the hydriodate is changed into ioduret. Liquid hydro-chloric acid does not decompose the hydriodates, because it is more volatile than hydriodic acid; but in the gaseous state it decomposes the iodurets in an elevated temperature. I passed slowly through a glass tube containing ioduret of potash that had been melted, a current of hydro-chloric gas. There was no decomposition while cold. When the temperature was raised nearly to a red heat, I obtained hydriodic gas containing but very little hydro-chloric gas. With the iodurets of strontium and calcium, the decomposition takes place much better. This method may be employed with advantage in order to procure hydriodic gas.

Iodureted Hydriodates.

All the hydriodates have the property of dissolving abundance of iodine, and by this they acquire a deep reddish-brown colour. They keep it in solution by a very weak force: for they let it go when boiled, or when exposed to the air after being dried. The iodine does not change the neutral state of the hydriodates; and the reddish-brown colour of the solutions, similar to the other solutions of iodine, is a new proof of the weakness of the combination. We cannot compare these compounds to the sulphureted sulphites, in which the sulphur appears to act the part of an acid. They have rather the characters of a simple solution. I am aware that combi

The prochlorurets of copper aud mercury are insoluble, while the deutochlorurets are very soluble. Though we may explain this difference on the hypothesis that chlorurets do not dissolve in water but in as much as they decompose it, these facts seem to me more favourable to the other hypothesis, that the chlorurets may dissolve in water without decomposing it. I have called the first combination of copper and mercury with chlorine prochloruret, because it corresponds with theit protoxides; and the second deutochioruret, because it corresponds with the second degree of their oxidation,

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