result might be more fortunate. Accordingly he caused a current of euchlorine gas, dried by passing through muriate of lime, to act upon iodine. A combination took place. When the solid body formed was exposed to a moderate heat, chloriode was driven off in the state of vapour, and an oxiode, or compound of oxygen and iodine, remained behind. This substance is solid, of a white colour, and considerable specific gravity, as it sinks rapidly in sulphuric acid. Its taste is astringent. It dissolves rapidly in water, and forms a colourless solution, which has acid properties, and which the author calls oxiodic acid. This liquid first reddens vegetable blues, and then destroys them. Other colours it converts into yellow. When the oxiode is exposed to a heat rather below the boiling point of olive oil, it is decomposed, oxygen gas being driven off, and iodine left behind. Sir H. Davy, from various experiments, made however on a small scale, considers this compound as composed of one atom of iodine and five atoms of oxygen. If we reckon the weight of an atom of iodine 15-621, and that of an atom of oxygen 1, this will give us the oxiode composed of 15.621 iodine and 5 oxygen, or of Iodine ... 75.75 100.00 Oxiodine has the property of combining with the different bases and forming oxiodes, which the author describes. The oxiodic acid likewise combines with the alkalies, earths, and oxides, and forms a class of salts, which he distinguishes by the name of oxiodates. This substance has the remarkable property of combining likewise with the different acids, and of forming solid compounds, which for the most part crystallize. When dropped into sulphuric acid, a solid substance falls, which, when heated, melts, and assumes, on cooling, the form of yellow-coloured rhombs. According to Sir H. Davy's experiments, this compound is composed of 20 oxiode and 8 sulphuric acid. He considers it as a hydrate. If we suppose it a compound of one integrant particle of oxiode and one integrant particle of sulphuric acid, it appears from the above analysis that there may be present in it two integrant particles of water. The oxiode combines also with phosphoric acid, phosphorous acid, nitric acid, and oxalic acid. These combinations are probably all hydrates. The oxiodic acid dissolves gold and platinum. When heated, the water is driven off, and the acid at last remains in the state of a thick paste. This paste is a hydrate of oxiodic acid. Sir H. Davy tried to obtain a compound of oxygen and iodine containing a less proportion of oxygen than the above-described oxiode; but his attempts were unsuccessful. The supposed combination of oxygen and iodine described by Gay-Lussac was a compound of oxiode and sulphuric acid, and contained likewise some barytes. LINNEAN SOCIETY. On Tuesday, the 4th of April, a paper by Dr. Leach was read on the classification of the insects called notonectides. On Tuesday, the 18th of April, a paper by the Rev. P. Keith was read, on the ascent of the sap in trees. Mr. Keith took a view of the different hypotheses hitherto proposed to account for the ascent of the sap, and showed that they were all inadequate to explain the phenomena. One of the latest of these hypotheses is that of Mr. Knight, who conceives that the ascent of the sap may be owing to what is called the silver grain of the wood. To refute this hypothesis, it is only necessary to mention that some of the tallest plants known have no silver grain whatever. Yet it is obvious that the sap ascends in them as well as in other plants. Mr. Keith considers the hypothesis of Saussure, that the sap is forced up by the contraction of the vessels, as with certain modifications, most likely to be true, GEOLOGICAL SOCIETY. March 17, 1815.-A communication was read from the Woodwardian Professor; the object of which paper is to describe a remarkable variety of geode, several individuals of which were lately met in digging a well at Oakhampton, Devonshire. They occurred in a bed of clay about ten feet deep. Their figure is nearly that of a compressed spheroid, and each ball consists of a nucleus of ochreous oxide of iron enclosed within a shell of a cavernous structure, the shells of which are externally so regular that the mass might easily be mistaken for a fossil madrepore. With regard to the mode in which this and similar bodies have been formed, the Professor suggests that the deposition of the beds in which they are formed might have been attended with effervescence, and that this spheroidal figure and cavernous structure might have been occasioned by gas uniformly distending, and at length escaping insensibly through the cellular crust by which it had been confined. The reading of Mr. Horner's paper on the south-western part of Somersetshire was continued. April 7.-A short notice from Mr. Horner on the locality of some specimens from the island of Tino, presented by him to the Society, was read; also a communication from the Woodwardian Professor, supplementary to his former, on the Cambridgeshire strata. This paper furnishes a new locality of the flattened Headington oyster, it having been lately found forming a strong bed at Willham, about six miles north of Ely, in the Fen level, a position which ascertains its geological situation to be below the chalk. Another remarkable appearance is stated to occur at Reche, not far from Swaffham, on the edge of the fen. This place has for ages supplied the surrounding country with the chalky lime-stone called clunch, in consequence of which extensive excavations have been formed, which have laid bare a large mass of a lenticular shape imbedded in the clunch. The greatest thickness of this mass is about eight feet, and its length and breadth from 30 to 40 yards. It is comprised of kidney-shaped masses, about the size of a walnut, of ochre-yellow lime-stone, covered superficially with a thin coat of green oxide of iron. It contains a few spines of an echinus completely converted into spar, and also vegetable impressions seemingly belonging to plants of the tribe of gramina. At this meeting the reading of Mr. Horner's paper on the southwestern part of Somersetshire was concluded. The most elevated ground in the district here described is Exmoor Forest and the Quantock Hills. This tract is composed for the most part of a grey-wacke formation; the strata of which present more or less coarsely-granular mixtures of quartz and clay, sometimes considerably calcareous, alternating with slaty beds, which often are not to be distinguished by external characters from primary clay-slate. Within these latter beds are included thick short beds of lime-stone full of madrepores, and containing veins and nests of grey copper malachite and hæmatite. In the ground of Hestercombe occurs a wall (probably a vein) of fine-grained grey granite; the slate rises up towards it at a very high angle, is conside ably indurated, and at the plane of junction appears to be more or less penetrated by the granite. Where the hills of grey-wacke sink down into the lower country their sides are covered with beds of conglomerate passing into red sand-stone, which extend to a considerable distance. These beds appear to consist of the same materials as the grey-wacke formation, but decomposed to a considerable degree. They are traversed by veins of calcareous spar, sometimes of so great a thickness as to be quarried for lime-stone. The conglomerate, with its accompanying sand-stones, is covered in many places by a red argillaceous sand-stone, containing a variable proportion of calcareous matter, but being principally characterized by spots and stripes of a greenish-grey colour. It is of an uniformly fine texture, never contains any fragments either angular or rounded, is in places traversed by veins of gypsum, and appears to be the same rock as that in which the salt-beds of Cheshire and Droitwich are situated. To this rock succeeds the strata of Lyas lime-stone, which with their accompanying beds of slate-clay are sometimes seen distinctly resting on the red gypseous rock, and sometimes in very broken and disturbed stratification appear to alternate with it. On the sea coast about three miles westward of the river Parrett, in the cavities formed by the curvature of the Lyas strata, is a stiff blue clay, covered with peat, in which are imbedded trunks of trees, often of great size, and with their lateral branches still attached to them. These remains of an ancient forest extend to an unknown distance into the sea. ARTICLE XII. SCIENTIFIC INTELLIGENCE; AND NOTICES OF SUBJECTS I. Lectures. The Summer Courses of Lectures on the Theory and Practice of Physic, by Dr. Roget, and of Materia Medica and Medical Jurisprudence, by Dr. Harrison, will commence, as usual, in Windmill-street, on the first week in May. The Lectures on Chemistry will, in consequence of Dr. Davy's absence from town, be given during the summer by Dr. Granville. Dr. Clutterbuck will begin his Summer Course of Lectures on the Theory and Practice of Physic, Materia Medica, and Chemistry, on Friday, June 2, at ten o'clock in the morning, at his house, No. 1, in the Crescent, New Bridge-street, Blackfriars, where further particulars may be had. II. Gas Lights. In answer to M., who puts some queries on the subject of gas lights in the last number of the Annals of Philosophy, p. 313, I have to observe that, in all my experiments on carbureted hydrogen gas I never was able to produce an explosion by firing any mixture of it whatever with common air. It merely burnt rapidly. Such a rapid combustion on a large scale I am sensible would produce an 'explosion. When mixed with oxygen gas, it will not fire unless it bear a certain proportion to the oxygen gas. The oxygen gas must amount at least to 105 measures (supposing we take 100 measures of carbureted hydrogen gas), and no explosion takes place whenever the oxygen amounts to 227 measures. From these facts, I infer that whenever 11 parts of common air and one part of carbureted hydrogen are mixed together, the mixture will explode when kindled; but if the carbureted bydrogen exceed th of the common air, it will no longer be capable of exploding. All proportions betweenth and 4th will explode. The gas produced by the distillation of pit-coal consists almost entirely of carbureted hydrogen. Hence I conceive that the preceding observations apply to it correctly; of course coal gas, when collected in reservoirs, never can explode unless it be mixed with at least six times its bulk of common air. This I think never can happen except from an unaccountable and culpable negligence of those who are employed. If the reservoir is not air-tight, if it be filled with coal gas, and the pressure by which it is made to sink in the water as the gas is expended be taken off, I can easily conceive that after an interval of a day or two (according to the size of the lack), five-sixths of the gas may make its escape, and be replaced by as much common air; for as coal gas is much lighter than common air, it will always make its escape when it can. I am persuaded that the explosion at Birmingham, and some others which I have heard of, were produced in this manner. But as nothing is easier than to ascertain whether the reservoir be air-tight, I conceive that with common precaution gas lights may be used with as much safety as any other light whatever. As to the coal that answers best, it is undoubtedly that variety which contains the greatest quantity of bitumen. Newcastle and Wigan coal will probably answer better than any other coal in the island, except some of the Fife coal, which is absolutely of the same quality. With respect to the degree of pressure requisite to make it issue with sufficient velocity from the mouth of the pipes, I do not know that any accurate experiments have been made to determine it, nor do I believe that much nicety is necessary. Some Gentlemen have expressed doubts on the subject, because Mr. Wilkinson was not able to force an efficacious draught of air through a pipe a few hundred feet in length; but the cases are by no means parallel. Mr. Wilkinson required a current of considerable velocity; but no such velocity is requisite for the coal gas. Besides, the water generated by the combustion of the coal gas at the extremity of the tube must occasion a diminution of pressure, which will serve to regulate the issue of -the coal gas from the reservoir. III. Toads found in Rocks and Trees. A correspondent at Bristol, I. B. I., has proposed some queries relative to the many stories in circulation respecting toads found in the middle of solid rocks. There can be no doubt that toads have been frequently found in such positions, though in no one case that I have seen has it been ascertained that the animal was completely excluded from the external air. I have myself conversed with workmen who had found toads both in coal-pits and in quarries; but they were never able to bring decisive proof that the animal was completely surrounded by the coal or the stone. It is generally observed that when a toad is found in this position the creature dies very soon after being brought out of its lurking hole. This seems to me a proof that the animal, if not entirely excluded from the air, must have been at least nearly so; for the sudden death can scarcely be ascribed to any thing else than the change of situation. IV. On the Focal Powers of the Eye. By Dan. Pring, Surgeon. It has been presumed from the supposed resemblance of the eye to some optical contrivances, that it is necessary the former should possess a variable focal power, in order to account for the capability of viewing objects at various distances. But this supposition appears |