discovered many years ago, and have always practised with success: if to 4 parts of scraped cheese be added one part of calcined oyster shells, or other pure calcareous earth, and this composition be pressed strongly into the pores of the wood, the sap will instantly cease to flow; the largest branch may of course be taken off at any season with safety.

Oximuriatic

V.

On some of the Combinations of Oximuriatic Gas and-Origen, and on the Chemical Relations of these Principles to Inflammable Bodies. By HUMPHREY DAVY, Esq. LL. D. Sec. R. S. Prof. Chem. R. I. F. R. S. E.*

1. Introduction.

In the last communication which I had the honour of pre

acid gas a sim-senting to the Royal Society, I stated a number of facts, ple substance, which inclined me to believe, that the body improperly

called in the modern nomenclature of chemistry oximuriatic acid gas has not as yet been decomposed; but that it is a peculiar substance, elementary as far as our knowledge extends, and analogous in many of its properties to oxigen gas.

My objects in the present lecture are to detail a number of experiments, which I have made for the purpose of illustrating more fully the nature, properties, and combinations of this substance, and its attractions for inflammable bodies, as compared with those of oxigen; and likewise to present some general views and conclusions concerning the chemical powers of different species of matter, and the proportions in which they enter into union.

I have been almost constantly employed, since the last session of the society, upon these researches, yet this time has not been sufficient to enable me to approach to any thing complete in the investigation. But on subjects, important

Phil. Trans. for 1811, P. 1.

both

both in their connexion with the higher departments of chemical philosophy, and with the economical applications of chemistry, I trust that even these imperfect labours will not be wholly unacceptable.

2. On the Combinations of Oximuriatic Gas and Oxigen with the Metals from the fixed Alkalis.

The intensity of the attraction of potassium for oximu- Potassium inriatic gas is shown by its spontaneous inflammation in this flames in oxi muriatic gas, substance, and by the vividness of the combustion. I satisfied myself, by various minute experiments, that no water is separated in this operation, and that the proportions of the compound are such, that one grain of potassium absorbs about 11 cubical inch of oximuriatic gas at the mean and forms a temperature and pressure, and that they form a neutral neutral compound unalcompound, which undergoes no change by fusion. I used, terable by fuin the experiments from which these conclusions are drawn, sion, a tray of platina for receiving the potassium; the metal was heated in an exhausted vessel, to decompose any water absorbed by the crust of potash, which forms upon the potassium during its exposure to the atmosphere, and the gas was freed from vapour by muriate of lime. Large masses of potassium cannot be made to inflame, without heat, in oximuriatic gas. In all experiments in which I fused the potassium upon glass, the retorts broke in pieces, in consequence of the violence of the combustion, and even in two instances when I used the tray of platina. If oximuriatic gas be used not freed from vapour, or if the potassium has been previously exposed to the air, a little moisture always separates during the process of combustion. When pure potassium, and pure oximuriatic gas are used, the result, as the same as muriate of pot. I have stated, is a mere binary compound, the same as mu- ash riate of potash, that has undergone ignition.

The combustion of potassium and sodium in oxigen gas Potassium and is much less vivid than in oximuriatic gas. From this sodium burn less vividly in phenomenon, and from some others, I was inclined to beoxigen than in lieve, that the attraction of these metals for oxigen is feebler, oximuriatic than their attraction for oximuriatic gas. I made several experiments, which proved that this is the fact; but before I enter upon a detail of them, it will be necessary to discuss VOL. XXIX.-JUNE, 1811.

I

more

gas.

When this is done on platina, the metal

oxided.

more fully, than I have yet attempted, the nature of the combinations of potassium and sodium with oxigen, and of potash and soda with water.

I have stated in the last Bakerian Lecture, that potassium and sodium, when burnt in oxigen gas, produce potash and soda in a state of extreme dryness, and very difficult of fusion. In the experiments from which these conclusions are drawn, as I mentioned, I used trays of platina, and finding that this metal was oxidated in the operation, I heated the retort strongly, to expel any oxigen the platina might have absorbed, and, except in cases when this precaution was taken, I found the absorption of oxigen much greater than could be accounted for by the production of Potassium and the alkalis. In all cases in which I burnt potassium or sodium burned sodium in common air, applying only a gentle heat, I found that the first products were substances extremely fusible, brown, fusible and of a reddish brown colour, which copiously effervesced in water, and which became dry alkali, by being strongly heated upon platina in the air; phenomena, which, at an early period of the inquiry, induced me to suppose that they were protoxides of potassium and sodium. Finding, in subsequent experiments, however, that they deflagrated with iron filings, and rapidly oxidated platina and silver, I suspended my opinion on the subject, intending to inves-. tigate their nature more fully.

in common

air produce

substances,

which are oxides.

per

When they

are formed on

metallic sub

Since that time, these oxides, as I find by a notice in the Moniteur for July 5th, 1810, have occupied the attention of Messrs. Gay-Lussac and Thenard; and these able chemists have discovered, that they are peroxides of potassium and sodium, the one containing, according to them, three times as much oxigen as potash, and the other 15 times as much as soda.

I have been able to confirin in a general way these interesting results, though I have not found any means of asstances these certaining accurately the quantity of oxigen contained in are always ox- these new oxides. When they are formed upon metallic substances, there is always a considerable oxidation of the metal, even though platina be employed. I have used a platina tray lined with muriate of potash, that had been fused; but in this case, though I am inclined to believe

ided.

that

that some alkali was formed at the same time with the peroxides, yet I obtained an absorption of 2.6 cubical inches, in a case when 2 grains of potassium were employed, and of 1.63 cubical inches, in a case when a grain of sodium was used, but in this last instance the edge of the platina tray had been acted upon by the metal, and was oxidated*. The mercury in the barometer in these experiments stood at 30.12 inches, and that in the thermometer at 62° Fahrenheit.

ties.

When these peroxides were formed upon muriate of Their properpotash, the colour of that from potassium was of a bright orange; that from sodium of a darker orange tint. They gave off oxigen, as Messrs. Gay-Lussac and Thenard state, by the action of water or acids. They were converted into alkali, as the French chemists have stated, by being heated with any metallic or inflammable matter. They thickened fixed oils, forming a compound, that did not redden paper tinged with turmeric, without the addition of water.

tassium on

When potassium is brought into contact with fused Action of pe nitre, in tubes of pure glass, there is a slight scintillation fused nitre. only, and the nitre becomes of a red brown colour. In this operation, nitrogen is produced, and the oxide of potassium formed. I thought that by ascertaining the quantity of nitrogen evolved by the action of a given weight of potassiuni, and comparing this with the quantity of oxigen disengaged from the oxide by water, I might be able to deter mine its composition accurately. A grain of potassium acting in this way, I found, produced only 0.16 of nitrogen; and the red oxide, by its action upon water, produced less than half a cubical inch of oxigen, so that it is probable, that potash as well as its peroxide is formed in the operation.

Sodium, when brought into contact with fused nitre, Action of so

Messrs, Gay-Lussac and Thenard have stated in the paper above re- Potash and baferred to, that common potash and barytes absorb oxigen when heated. rytes absorb It would seem, that the action of the fixed alkalis and of barytes on pla- oxigen when heated, tina depends on the production of the peroxides. I have little doubt, but that these ingenious gentlemen will have anticipated this observation, in the detailed account of their experiments. 12

produced

nitre.

dium on fused produced a violent deflagration. In two experiments in which I used a grain of the metal, the tube broke with the violence of the explosion. I succeeded in obtaining the solid results of the deflagration of a grain of sodium; but it appeared, that no peroxide had formed, for the mass gave no oxigen by the action of water.

Potassium

When potassium is burnt in a retort of pure glass, the burned in a re result is partly potash and partly peroxide, and by a long continued red heat the peroxide is entirely decomposed.

tort of pure

glass,

and in one of green glass

igen.

A grain of potassium was gently heated in a small green containing ox- glass retort containing oxigen; it burnt slowly, and with a feeble flame; a quantity of oxigen was absorbed equal to 0-9 of a cubical inch; by heating the retort to dull redness, oxigen was expelled equal to 0.38 of a cubical inch; the mercury in the thermometer in this experiment stood at 63° Fahrenheit, and that in the barometer at 30°1 inches.

Electrical decomposition of potash and soda.

Supposed prot. oxides.

In experiments on the electrical decomposition of potash and soda, when the Voltaic battery employed contains from 500 to 1000 series in full action; the metals burn at the moment of their production, and form the peroxides; and it is probable, from the observations of Mr. Ritter, that these bodies may be produced likewise in Voltaic operations on potash, at the positive surface.

In my early experiments on potassium and sodium, I regarded the fusible substances appearing at the negative surface, in the Voltaic circuit, as well as those produced by the exposure of the metals to heat and air, as protoxides, and as similar to the results obtained by heating the metals in contact with small quantities of alkali.

I have repeated these last operations, in which I conceived that protoxides were formed.

Potassium and sodium, when heated in glass tubes in contact with about half of their weight of potash and soda, that have been ignited, become first of a bright azure, then produce a considerable quantity of hidrogen, and at last form a gray coherent mass, not fusible at a dull red heat, and which gives hidrogen by the action of water.

Whether these are true protoxides, or merely mixtures of the alkaline metals with the alkalis, or with the alkalis and reduced