Sidebilder
PDF
ePub

tions which the Author's opportunities have enabled him to collect, and we hope it will stimulate others to preserve and communicate similar records of cases which come under their notice. We frankly confess our inability to do justice to the communication, by any abstract which our limits would allow, and we shall, therefore, merely transcribe the heads or sections under which the observations are classed. These are—the effects produced by an undue pressure of water upon the brain—by concussion— by the preternatural dilatation or disease of blood vessels—by the extravasation of blood—by the formation of pus—by the depression and thickening of different portions of the skull—by the pressure of tumours—by injury done to the substance of the brain—by alterations of structure from disease—and by injury done to the spinal marrow.

Further Experiments and Observations on Iodine. By Sir H.Davy, LL.D. F. R. S. V.P.R.I.

This paper contains some additional observations on the triple compounds containing iodine and oxygen, which are analogous to the hyperoxymuriates; on the hydroionic acid, and its compounds; on the other acid compounds of iodine; on the action of some compound gases upon it, and on the means of detecting it in its combinations; and on certain properties of its combination with sodium.

In order to obtain the triple combination of iodine and oxygen, with the fixed alkalies, it is necessary to boil the products repeatedly in small quantities of alcohol, of specific gravity from 8. 6 to 9. 2, the binary combination of iodine with the alkali is thus removed, as the alcohol dissolves it readily, but has very little action on the triple compound. The experiments of Sir H. were made with the triple compound of potassium, as being most easily procured; but the properties of that with a base of sodium appear to be precisely analogous. When pure, it is nearly tasteless; it has no action on vegetable colours; is scarcely soluble in cold water ; but more so in that which is made hot; and when thrown into concentrated sulphuric, nitric, or phosphoric acids, it has no violent action upon them; but aided by heat, it is dissolved in them, and solid crystallized compounds are formed, which are intensely acid. If its combination with nitric acid is strongly heated, the nitric acid is driven off, and at the temperature at which it is entirely expelled, the compound itself begins to decompose, and to afford a little iodine, and a considerable proportion of oxygen. If the combination which it forms with sulphuric or phosphoric acid, is heated to the degree at which the acids are sublimed, the triple compound is itself decomposed, oxygen and iodine are separated, and acid sulphate

Rr 2 '.. "."',' '■'.' " ."

or phosphate of potash remains. If when the combination is rendered fluid by heat, a little sugar, or other combustible matter is added to it, there is violent action, and the iodine is disengaged with great rapidity. The triple compound dissolves •without decomposition in phosphorus acid; '-tit \vhen the solution is heated, the acid attracts the oxygen, the iodine is set at litoeriy, nnd phosphate of potash is formed. If it is thrown into muriatic acid, there is an effervescence, the odour of chlorine becomes evident, the liquid becomes yellow, and when evaporated it yields chlorionic acid. When the solution of hydroionic acid in water is poured upon the triple salt, iodine is instantly produced in considerable quantity. Acetic and oxalic acids dissolve the triple compound without decomposing it; but on heating the solution in oxalic acid, charcoal is deposited, and the iodine immediately appears. When it is dissolved in sulphureous acid, iodine is immediately produced, and the acid is converted into the sulphuric, and if the quantity of acid is not too large, it dissolves part of the iodine and becomes yellow.

The binary compound of iodine and potassium has no action on oxalic, acetic, sulphurous, or phosphorous acid, except it is mixed with the triple compound, when it is immediately decomposed by these acids, and the iodine is set free The double compound in its pure state is very slowly decomposed by muri- ,atic acid; but when a mixture of the binary and triple compound is exposed to the action of this acid, muriate of potassa is instantly formed; and if the proper proportions are used, none of the salts remain, the results being only muriate of potassa, and oxychloric acid. A mixture of the binary and triple compounds, acted upon by glacial hydrophosphoric acid, affords iodine in large quantity, but the binary compound alone yields only hydroionic acid, and Sir H. recommends this as the best mode of procuring this acid in a pure form. From a comparative estimate of several analyses, Sir II. thinks the triple compound consists of one proportion of iodine, one of potassium, and six of oxygen. He proposes for these compounds the name of oxy-iodes, the specific appellation being derived from the base to which the oxygen and iodine are united.

The best method of procuring hydroionic acid is by the action ofhydrophosphoric acid on the binary compound of iodine and potash. It is rapidly decomposed by being heated in its gaseous form, in contact with oxygene, a solution of iodine, and hydroionic acid in water being formed. It is also slowly decomposed by heat alone, affording a deep red brown, easily fusible substance, which appears to be a combination of hydroionic jjas in with iodine. When the acid gas is condensed in water, it is instantly decomposed by nitric acid, iodine being precipitated. The solution of hydroionic acid gas in water, absorbs oxygeue rapidly from the atmosphere, becoming first yellow, and afterwards of a deep tawny orange colour. The.flbsorption of oxygen is assisted by light and heat; and Sir H. thinks the concentrated acid will probably form an eudomietrical • i i;>n superior to any which we at present possess It is decomposed by being heated with hyperoxymuriate of potash, iodine being disengaged. It is decomposed also in solution, as wcil as in the gaseous state, by all the metals with which it has been tried, except gold and platinum ; but in some cases it requires the assistance of heat. The liquid acid tarnishes silver at common temperatures, and slowly dissolves mercury when boiled upon it. It dissolves the alkaline and common earths, and forms •with them compounds strikingly analogous to the salts which they form when combined with muiiatic acid.

The acid formed by the combination of iodine with chlorine, is extremely volatile. It appears probable, from several experiments on the proportions in which these bodies unite to form chlorionic acid, that it consists of one proportion of iodine united to one of chlorine; but they are evidently capable of combining in different proportions. The acid formed by the sublimation of iodine in chlorine in great excess, is of a bright yellow colour; when fused it becomes of a deep orange colour, and when sublimed it forms a deep orange-coloured gas. It is still capable of uniting with much iodine when they are heated together, its colour becomes consequently deeper, and they rise together in the gaseous state. The solution of the acid in water, also dissolves iodine in large quantity, so that the proportions in which they combine may admit of considerable range. The pure solution of chlorionic acid much diluted, loses its colour when agitated in contact with chlorine for some time; and in this state, when poured into solutions of the alkaline salts or alkaline earths, it causes a precipitation of substances, having the properties of the triple compounds called oxyiodes.

If the acid is in its ordinary state, or has not been rendered colourless by agitation with chlorine, at the same time that the oxyiode is thrown down when it is added to an alkaline solution, a considerable quantity of iodine is disengaged; and if the acid solution is concentrated, it cannot be deprived of this property. It throws down a precipitate from muriate of baryta, which has all the properties of an oxyiode, and the liquid becomes at the same time very acid. The colourless acid, added to a strong solution of ammonia, occasions the precipitation of acohite powder, which detonates feebly at a low temperature, the products being iodine, and a gas which does not support combustion; with the highly coloured acid, the precipitate from a solution of ammonia is black, and detonates with much greater force, by the slightest touch or motion. It appears to be the same substance as is procured by the direct action of iodine on ammonia, which is a compound of that body with acote. Chlorionic acid occasions a copious precipitation when added to solutions of the metallic salts ; and as the action is unaccompanied by any effervescence, Sir H. presumes, from analogy, that the precipitate consists of a triple combination of the metal with iodine and oxygene. Sulphate of iron, nitro-muriate of lead and tin, and nitrate of copper, are the only metallic salts with which the experiment appears to have been made.

Of the compound gases, Sir H. has submitted iodine to the action of sulphuretted hydrogene, olefiant gas, nitrous gas, and carbonic oxide. It combines with sulphuretted hydrogene, forming a reddish brown-coloured liquid, which when thrown into water is decomposed, hydroionic acid being formed, and sulphur precipitated. By subliming iodine repeatedly in dry olefiant gas, a small quantity of a reddish-brown liquid was formed, which is volatile at a low temperature, and gives a yellow tint to water, but does not make it acid. The quantity of gas absorbed is very small. Iodine has no effect on nitrous gas; nor was any combination effected by subliming it in carbonic oxides in ordinary day light: but when the vessel containing carbonic oxide and iodine in a gaseous state was exposed to the direct rays of the sun, a small quantity of a limpid fluid, having an acrid taste, was formed; so that it is probable, like chlorine, it may be combined with carbonic oxide by the action of solar light.

The best test of the presence of iodine in any compound, is afforded by its action upon silver. Water which contains less than T^ot part of its weight of the double or triple alkaline compound, tarnishes polished silver, and the effect produced by the compounds of iodine may be distinguished by this circumstance from that produced by the alkaline sulphurets or sulphuretted hydrogene, that the solutions containing sulphurets lose their power of tarnishing silver, by being boiled slightly with a little muriatic acid, but those which contain iodine do not.

Sir H. examined specimens of alkali produced from vegetables growing on the sea shore, from Sicily, from Spain, and from the Roman states, without obtaining any indications of the presence of iodine; nor did he gain any unequivocal evidence of its existence by the evaporation of sea-water taken up on the coast of Liguria, in a part of the bay remote from any source of fresh water. But the first crystals of salt which were formed, appeared to him to tarnish silver on which they were fused more than the last. It is scarcely possible to doubt that iodine does exist in sea-water in minute quantity, and Sir H. thinks it is probably in a state of triple union with oxygene and sodium, and that it is separated with the first crystals of muriate of soda which are formed. Sir H. thinks it not improbable that the superiority of bay-salt over rock-salt, in preserving meat and fish, may be owing to the presence of a minute quantity of this singular body. Some of the binary and triple compounds of iodine with sodium, were rubbed on pieces of beef which had been several days killed, and they did not putrify.

[graphic]

Observations respecting the natural Production of Saltpetre on the Walla of subterraneous and other Buildings. By John Kidd, M. D. Professor of Chemistry at Oxford.

This is an ingenious paper, but it is not susceptible of abridgement, nor does it throw any new light upon the most curious and obscure part of the subject to which it relates, viz. the source of the potash which is contained in the nitre, and the existence of which in the situations where nitre spontaneously forms, is unsupported by any evidence which is not entirely gratuitous. Observations conducted with the minuteness and accuracy which characterize this paper, and connected with more refined analytical researches, can alone afford any satisfactory elucidation of the subject.

On the Nature of the Salts termed triple Prutsiateit, and on Acids formed by the Union of certain Bodies with the Elements of the Prussic Acid. By Robert Porrett, jun. Ksq.

This is an elaborate communication which opens some uew •and interesting views of the nature of Prussic acid, and its com •binations. The object of the paper is very clearly stated by •its Author, to be 'to reconcile with the general properties of 'other saline bodies the anomalies which the triple prugsiates '• present; to simplify the received opinion respecting their na- 'ture, and to make known some new acids which 1 have dis'covered.' Mr. Porrett considers the class of salts which have been termed triple Prussiates, as binary compounds, of which the acid is not the Prussic, but a new acid into which the black oxide of iron enters as a component part, that substance being superadded to the other elements of Prussic acid in order to its formation. The evidences adduced in support of this view of the subject, in addition to the anomalies which •ucumberthe received theory, are, the results of the decomposition of the triple Prussiates by the Voltaic battery, and also by the agency of ordinary chemical affinities. Triple Prussiate of soda was exposed to a battery of small plates for twenty hours, and the soda was attracted to the negative pole, the iron passing over with the other elements of the Prussic acid to the positive

[graphic]
« ForrigeFortsett »