an experiment of this kind, the deviation was about 159 in the morning and evening, but more considerable in the course of the day. This first attempt has made me suppose that the galvanbe meter might become, in the hands of an attentive and skilful philosopher, a kind of atmidometer. If by means of a single couple of two different metals, bismuth and copper, a deviation of 15° has been obtained, a much greater one would be produced by employing several pairs, conveniently immersed in the same vessel of water; and, perhaps, one might succeed by increasing the scale of observation, in ascertaining more exactly the diurnal rate of evaporation. I propose, also, to ascertain the effect of a current of air, excited by any means over the surface of the water used in the experiment; it would, without doubt, augment the evaporation, and by increasing the difference between the temperature of the air and the water, increase the effect on the instrument.-Bib. Univ. xxix. 119.

いま

3. On the Length of the Electric Flash producing Lightning. By M. Gay Lussac.-The length of the flash during storms is always very great, and one may readily ascertain, in a mountainous country, that it frequently exceeds a league. This extraordinary length, and the awful sound produced by the flash, induces us naturally to admit, that the quantity of electricity which forms it is incomparably greater than that which may be accumulated in the largest electric batteries. We cannot produce explosion except at the distance of a few centimetres, (an inch or two,) and the intensity which we must suppose is required in batteries to make an explosion at the distance of a few metres, (or a few yards,) only, would be so great as to make it impossible it could be retained on a coated surface by the pressure of the air. On the other side, when lightning falls on a lightning-rod, it frequently happens that only a small portion of the point, perhaps three or 'four millimetres, (0.12 to 0.16 of inch,) is fused; and this effect is not very different to what may be produced by large electrical batteries.

But we cannot really judge of the intensity of electricity accumulated on our conductors, and on a thunder-cloud by the length of the spark. The electricity is retained on our conductors by the pressure of the air, the spark only occurs when this pressure can be overcome by the electricity. On the contrary, the electricity is retained on a cloud only by the resistance it affords to it as a non-conducting body, and equally pressed as it is by this fluid which surrounds it on all sides, it should obey the slightest attractive or repulsive forces by which it is affected. We may therefore conceive, that as soon as the electricity has -formed a stratum, no matter how attenuated, so that it be continuous, the flash may occur and pass through considerable dis?

tances.

81

The intensity of the flash will be produced by the quantity of electricity contained in the immense stratum enveloping the cloud. If the stratum is not continuous, which is very possible in so bad a conductor as a cloud, or if all the electricity spread over the space occupied by the cloud has not had time to disengage itself, so as to arrive at the surface of the cloud, the discharge will only be partial, and then the redoubled peals of thunder will easily be understood. It appears impossible to us, according to these observations, that the thickness of the electric stratum can ever be any thing like so great on the surface of a thunder cloud as on that of a solid conductor; for the repulsion of its molecules would dissipate it in the air. We perceive nothing to retain it but the resistance of the air as a non-conductor, and that resistance can be but very small.

9

2

As the primitive electricity spread over the space occupied by a thunder-cloud can unite but very slowly into a thin stratum, it becomes difficult, according to the theory of Volta, to attribute to it the formation of hail in particles as large as those which are sometimes observed; the phenomenon, however, is certainly connected with atmospheric electricity; and though we are not acquainted with all the circumstances which would enable us to comprehend it, we must not reject a cause because it appears to us not to have an intensity proportional to the effects we would explain. Ann. de Chim, xxix. 105.

4. On the Existence of Iodine in a Mineral Substance. By M. Vauquelin.-The mineral in which M. Vauquelin has, for the first time, found this peculiar substance, was brought by M. Joseph Tabary from the neighbourhood of Mexico, and was labelled virgin silver in serpentine. It was of a whitish colour on its rubbed surface, presenting grains of metallic silver; its fracture was lamellated, and of a yellowish green colour, with some black portions and metallic silver. Twenty parts of the substance were acted upon by nitric acid with effervescence; being boiled with it for some time, and then diluted, two insoluble portions appeared; one very heavy, and falling instantly, whilst the other was light, and remained in suspension. When sepa

rated and washed, the first weighed 6.12 parts; it fused easily by the blow-pipe, producing a purple flame, and ultimately, a small globule of silver appeared in the centre of a fused mass like chloride of lead. The edges of the charcoal were covered with a yellow powder. The lighter matter was brown, and weighed 2,7 parts; it burnt, producing sulphurous acid, and leaving sulphuret of lead with a little iron 1.58 parts.

A portion of the first matter, heated with muriatic acid, gave a red brown colour, and produced slight effervescence with, the odour of chlorine. As the temperature rose the effervescence inft on: Levounit

creased, and a beautiful violet colour was developed, în consequence of which the vessel was removed from the fire. There remained at the bottom of the acid a yellow substance, containing grey particles, which were dissolved by the hot water used for washing. This water had acquired a brown colour, and the power of colouring solution of starch of a fine blue. After many washings with water, alcohol was used, which in its turn became deeply coloured, and rendered a solution of starch of blue colour. In consequence of these appearances the muriatic solution was diluted and distilled, when violet vapour arose, and crystals of iodine condensed in the vessel. Though the yellow matter had boiled some moments with the muriatic acid, it still contained iodine, for 2.38 parts fused with two parts of potash, the residue dissolved in water, saturated with sulphuric acid, and mixed with starch, gave, with a few drops of chlorine, a fine blue colour; 1.63 grains of metallic silver were left.

Five parts of the mineral were then mixed with two parts of eaustic potash, and heated to redness for some time, after which treated with water 4.46 parts were left; these acted upon by nitric acid dissolved without effervescence, leaving a yellow substance resembling chloride of silver; when dried it weighed 0.8, and was ascertained to be iodide of silver; it gave 0.415 of silver to nitric acid.

Hence it appears that as the potash had taken 0.5 parts from the five originally used, which were iodine, and that 0.8 of iodide of silver were formed, which would contain 0.425 iodine, the whole quantity of iodine was 0.925, which divided by 5-0.185, or 18.5 per cent. in the mineral.

The alkaline solution before mentioned, saturated by nitric acid, became yellow; and added to solution of starch, with a little chlorine rendered it blue. Nitrate of mercury precipitated it red. A portion of it neutralized by sulphuric acid evaporated to dryness, digested in alcohol, and the alcoholic solution evaporated, gave quadrangular crystals of hydriodate of potash.

Besides iodine and silver, the mineral contained sulphur, lead, and carbonate of lime. M. Vauquelin considers it as probable, that the sulphur is combined with the lead and silver, and the iodine with a part of the silver. In confirmation of this it is said, that when boiled with ammonia for some time, iodide of silver is separated from it. This, however, is against the generallyreceived opinion, that the iodide of silver is insoluble in ammonia. Ann. de Chim. xxxix. 99.

5. Selenium in the Sulphur of the Lipari Islands. Amongst the volcanic productions of the Lipari Islands is a sal-ammoniac, with sulphur in alternate white and brownish orange layers. The colour of the latter has generally been attributed to iron, but the

usual tests gave no indications of that metal; arsenious acid, however, being detected. On dissolving the sal-ammoniac in water, a brownish residuum was left, which fused readily in a glass tube, and gave an orange-coloured sublimate. On hot coals it inflamed, evolving at first a mixed odour of sulphur and arsenie, and then the offensive smell of selenium. By digestion in nitric acid, till the orange colour disappeared, a solution was obtained, which, with sulphite of potash, threw down much of a cinnabarcoloured precipitate, possessing all the characters of selenium, whilst the solution evaporated gave acicular crystals of selenic acid. This discovery by M. Stromeyer of selenium amongst the volcanic products of the Lipari Islands, renders it probable that the peculiar orange tint of the sulphur, found in those islands, proceeds chiefly from selenium, and not, as hitherto supposed, from arsenie combined with the sulphur.-Ann. Phil. N. S. x. 234.

6. Natural Sources of Carbonic Acid Gas.-Bischoff and Nöggerath, in Schweigger's Journal, mention a pit on the side of the Lake of Laach, in which they found many dead animals, as birds of different kinds, squirrels, bats, frogs, toads, and also insects. On descending into the pit, and gradually sinking the head, they experienced the same sensation as when held over a vat in a state of fermentation. The quantity of gas evolved varies at different times. This evolution of carbonic acid gas is more striking in the volcanic Eifel. On the right bank of the river Kyll, nearly opposite to Birresborn, there is a spring named Brudelreis; a provincial name for a boiling spring, and applied to this because it is perpetually agitated by large bubbles of gas, the agitation being so great as to produce a noise heard four hundred yards off. In its vicinity numerous dead birds are found, killed by the carbonic acid rising from the water; and persons who kneel to drink at the spring are driven back by the gas. As MM. Bischoff and Nöggerath approached this spring, they heard the noise of its ebullition at a considerable distance, and by approaching their faces to the surface of the turf in the vicinity of the spring, found that it was covered with a layer of carbonic acid gas. They did not observe any deleterious effects produced on the surrounding trees or grass. On emptying the basin no more water was collected, shewing that it was rain, not spring water; but the gas continued to rise through the fissures of the rock in some places, with such force as to feel to the hand like wind from a bellows. Lime-water poured into one of the fissures became turbid, and caused the appearance of ebullition again, but it was not ascertained whether the gas was pure carbonic acid or not.-Edin. Phil. Jour. xiii. 191.

7. Process for the Detection of Phosphate of Lime,-A process

is given, as one recommended by MM. Vauquelin and Thenard, for the detection of phosphate of lime, founded upon its conversion by potassium into a phosphuret, and the production of phosphuretted hydrogen, either with water or acids, by the latter body. The gas is recognised by its well-known odour, and indicates the pres sence of a phosphate in the matter originally used. The decompo-I sition is to be effected in a glass tube, 3 or 4 millimetres (0.15 inch) in diameter, and about 4 centimetres (1.5 inches) long; a centi gramme (0.15 grain) of potassium is to be placed at the bottom, and the substance supposed to contain the phosphate in powder is ta be pressed down upon it. The tube is then to be gradually heated, the potassium sublimed through the substance, and, when cold, the excess of potassium removed by the introduction of mercury. The matter remaining, when exposed to a moist air, or when touched by muriatic acid, will evolve the odour of phosphuretted hydrogen, if any phosphate were present; or a little diluted acid may be introduced into the tube, and the gas evolved obtained. Of course, any sulphate which may be present must be removed, or the odour of sulphuretted hydrogen would seriously interfere with the delicacy of the test.-Jour. de Chim. Méd. Jan. 1825.

8. Metallic Titanium in Iron Furnaces.-Cubic crystals of metallic titanium, similar to those discovered by Dr. Wollaston in the iron-furnaces of South Wales, have also been found by Dr. Walchner, of Friburg, in the Breisgau, in the founderies of the highlands of Baden. The piece of slag examined was from the high furnace of Kandern, in which pea-iron ore only is smelted. Being desirous of ascertaining the presence of the titanium in the pea-iron ore, an attempt was made with the blow-pipe, and its presence, Dr. Walchner says, indicated, though in very small quantity. Phil. Mag. lxvi. 124.

9. Rose on the Separation of Titanic Acid from Oxide of Iron.― The difficulty of separating titanic acid from oxide of iron, is well known to chemists, no process but what is very imperfect being as yet known. M. Rose, who has had frequent occasion to combat this difficulty, has discovered and published a method which not only renders analytical processes more perfect, but very much facilitates the preparation of titanic acid from its more abundant natural compounds.

A solution of titanic acid and oxide of iron being obtained in muriatic acid, if tartaric acid be added to it, and the whole be diluted with water, then a great excess of caustic ammonia may be added without the smallest precipitate of titanic acid or oxide of iron being produced. If to this solution hydrosulphuret of ammonia be added, it exerts no action on the titanic acid, but changes all the oxide of iron into sulphuret, which separates perfectly.