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effervescence, with a loud hissing noise; it combines with the oxygen of the water to form soda, which is dissolved, and its hydrogen is disengaged. In this operation there is no luminous appearance, and it seems probable that even in the nascent state hydrogen is incapable of combining with it.*

When the basis of soda is thrown into hot water the decomposition is more violent, and in this case a few scintillations are generally observed at the surface of the fluid; but this is owing to small particles of the basis which are thrown out of the water sufficiently heated to burn in passing through the atmosphere. When, however, a globule is brought in contact with a small particle of water, or with moistened paper, the heat produced (there being no medium to carry it rapidly) is usually sufficient for accension of the basis.

The basis of soda acts upon alkohol and ether precisely in a similar manner with the basis of potash. The water that they contain is decomposed, soda is rapidly formed, and hydrogen disengaged.

The basis of soda, when thrown upon the strong acids, acts with great energy. When nitrous acid is employed, a vivid inflammation is produced; with muriatic and sulphuric acid there is much heat generated, but no light.

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When plunged by proper means beneath the surface of the acids, it is rapidly oxygenated; soda is produced, and the other products are similar to those generated by the action of the basis of potash. With respect to the fixed and volatile oils and naphtha in their different states, there is a perfect coincidence between the effects of the two new substances, except in the difference of the appearances of the saponaceous compounds formed; those produced by the oxydation and combination of the basis of soda being of a darker colour, and apparently less soluble.

* The more volatile metals seem capable of uniting with hydrogen, a circumstance presenting an analogy.

The basis of soda, in its degrees of oxydation, has precisely similar habits with the basis of potash.

When it is fused with dry soda in certain quantities, there is a division of oxygen between the alkali and the base, and a deep brown fluid is produced, which becomes a dark grey solid on cooling, and which attracts oxygen from the air, or which decomposes water and becomes soda.

The same body is often formed in the analytical processes of decomposition; and it is generated when the basis of soda is fused in tubes of the purest plate glass.

There is scarcely any difference in the visible phenomena of the agencies of the basis of soda and that of potash on sulphur, phosphorus and the metals. It combines with sulphur in close vessels filled with the vapour of naphtha with great vividness, with light, heat, and often with explosion from the vaporization of a portion of the sulphur, and the disengagement of sulphureted hydrogen gas. The sulphureted basis of soda is of a deep grey colour.

The phosphoret has the appearance of lead, and forms phosphate of soda by exposure to air or by combustion. The basis of soda, in the quantity of one-fortieth, renders mercury a fixed solid, of the colour of silver, and the combination is attended with a considerable degree of heat.

It makes an alloy with tin without changing its colours, and it acts upon lead and gold when heated. I have not examined its habitudes with any other metals; but in its state of alloy it is soon converted into soda by exposure to air, or by the action of water, which it decomposes with the evolution of hydrogen.

The amalgam of mercury and the basis of soda seem to form triple compounds with other metals. I have tried iron and platina, which, I am inclined to believe, remain in combination with the mercury when it is deprived of the new substance by exposure to air. The amalgam of the basis of soda and mercury likewise combines with sulphur, and forms a triple com-. pound of a dark grey colour.

VI. On the Proportions of the peculiar Basis and Oxygen in Potash and Soda.

The facility of combustion of the bases of the alkalies, and the readiness with which they decompound water, offered means fully adequate for determining the proportions of their ponder able constituent parts. I shall mention the general methods of the experiments, and the results obtained by the different series, which approach as near to each other as can be expected in operations performed on such small quantities of materials.

For the process in oxygen gas I employed glass tubes containing small trays made of thin leaves of silver or other noble metals, on which the substance to be burned, after being accurately weighed or compared with a globule of mercury equal in size,* was placed: the tube was small at one end, curved, and brought to a fine point, but suffered to remain open; and the other end was fitted to a tube communicating with a gasometer, from which the oxygen gas was introduced, for neither water nor mercury could be used for filling the apparatus. The oxy. gen gas was carried through the tube till it was found that the whole of the common air was expelled. The degree of its purity was acertained by suffering a similar quantity to pass into the mercurial apparatus. The lower orifice was then hermetically sealed by a spirit-lamp, and the upper part drawn out and finally closed, when the aperture was so small as to render the temperature employed incapable of materially influencing the volume of the gas; and when the whole arrangement was made, the combination was effected by applying heat to the glass, in contact with the metallic tray.

* When the globules were very small the comparison with mercury, which may be quickly made by means of a micrometer, was generally employed as the means of ascertaining the weight; for in this case the globule would be immediately introduced into the tube, and the weight of the mercury astertained at leisure.

In performing these experiments many difficulties occurred. When the flame of the lamp was immediately brought to play upon the glass, the combustion was very vivid, so as sometimes to break the tube, and the alkali generated partly rose in white fumes, which were deposited upon the glass.

When the temperature was slowly raised, the basis of the alkalies acted upon the metallic trays and formed alloys; and in this state it was very difficult to combine them with their full proportion of oxygen; and glass alone could not be employed on account of its decomposition by the alkaline basis; and porcelain is so bad a conductor of heat, that it was not possible to raise it to the point required for the process without softening the glass.

In all cases the globules of the alkaline basis were carefully freed from naphtha before they were introduced; of course a slight crust of alkali was formed before the combustion; but this could not materially affect the results; and when such a precaution was not used, an explosion generally took place from the vaporization and decomposition of the film of naphtha surrounding the globule.

After the combustion the absorption of gas was acertained by opening the lower point of the tube under water or mercury. In some cases the purity of the residual air was ascertained; in others the alkali formed in the tray was weighed.

From several experiments on the synthesis of potash by combustion, I shall select two which were made with every possible attention to accuracy, and under favourable circumstances for a mean result.

In the first experiment 0.12 grains of the basis of soda were employed. The combustion was made upon platina, and was rapid and complete; and the basis appeared to be perfectly saturated, as no disengagement of hydrogen took place when the platina tray was thrown into the water. The oxygen gas ab-.. sorbed equalled in volume 190 grains of quicksilver, barometer being at 29.8 inches, thermometer 62o Fahrenheit, and this

reduced to a temperature of 60° Fahrenheit, and under a pressure equal to that indicated by 30 inches* would become 186.67 measures; the weight of which would be about .0184 grains troy, but .0184: .1384 :: 13. 29: 100; and, according to this estimation, 100 parts of potash will consist of 86.7 basis, and 13.3 oxygen nearly.

In the second experiment .07 grains of the basis absorbed at temperature 63o of Fahrenheit, and under pressure equal to 30.1 barometer inches, a quantity of oxygen equal in volume to 121 grains of mercury; and the proper corrections being made, as in the former case, this gas would weigh .01189 grains.

But as .07+01189.08.189: 07:: 100: 85.48 nearly, and 100 parts of potash will consist of 85.5 of basis, and 14.5 of oxygen nearly; and the mean of the two experiments will be 86.1 of basis to 13.9 of oxygen for 100 parts.

In the most accurate experiment that I made on the combustion of the basis of soda, .08 parts of the basis absorded a quantity of oxygen equal in volume to 206 grains of mercury; the thermometer being at 56° Fahrenheit, and the barometer at 29.4; and this quantity, the correction being made as before for the mean temperature and pressure, equals about .02 grains of oxygen.

And as .08+02.10 : .08 :: 100: 80, and 100 parts of soda, according to this estimation, will consist of 80 basis to 20 oxygen.

In all cases of slow combustion, in which the alkalies were not carried out of the tray, I found a considerable increase of

* In the correction for temperature the estimations of Dalton and Gay-Lussac are taken, which make gasses expand about of the primitive volume for every degree of Fahrenheit.

† From experiments which I made in 1799 on the specific gravity of oxygen gas, it would appear that its weight is to that of water as 1 to 718, and to that of quicksilver as 1 to 10142. Researches Chem. and Phil. p. 9, and with this estimation, that deducible from the late accurate researches of Messrs. Allen and Pepys on the combustion of the diamond, almost precisely agrees. Phil, Trans. 1807, p. 275.

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