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tube till it was found that the whole of the common air, was expelled. The degree of its purity was ascertained by suffering a small quantity to pass into the mercurial apparatus. The lower orifice was then hermetically. sealed by a spirit-lamp, and the upper part drawn outand 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 metal-, lic tray.

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 al- . kali generated partly rose in white fumes, which were deposited upon the glass.

When the temperature was slowly raised, the bases of the alkalies acted upon the metallic tray, 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 bases; 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 bases 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 result; and when such a precaution was not used, an explosion generally took place from the vaporization

and

and decomposition of the film of naphtha surrounding the globule.

After the combustion, the absorption of gas was ascertained, 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 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 water. The oxygen gas absorbed equalled in volume 190 grains of quicksilver; barometer being at 29.6 inches, thermometer 62° 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 ac

of the

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

From experiments that I made in 1799, on the specific gravity of oxygen gas, it would appear that its weight is to that of water as ito 748, 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 combus, tion of the diamond almost precisely agrees. Phil. Trans. 1807, page 275,

cording

cording 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 630 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+.01189.08189:07:: 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.

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In the most accurate experiment that I made on the combustion of the basis of soda, .08 parts of the basis absorbed 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 quan-tity, the correctious 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 of oxygen.

In all cases of slow combustion, in which the alkalies were not carried out of the tray, I found a considerable increase of weight, but as it was impossible to weigh them except in the atmosphere, the moisture attracted rendered the results doubtful; and the proportions from the weight of the oxygen absorbed are more to be depended on. In the experiments in which the processes of weighing were most speedily performed, and in which no alkali adhered to the tube, the basis of potash gained nearly

nearly two parts for ten, and that of soda between three and four parts.

The results of the decomposition of water by the bases of the alkalies were much more readily and perfectly obtained than those of their combustion.

To check the rapidity of the process, and, in the case of potash, to prevent any of the basis from being dissolved, I employed the amalgains with mercury. I used a known weight of the bases, and made the amalgams under naphtha, using about two parts of mercury in volume to one of basis.

In the first instances I placed the amalgams under tubes filled with naphtha, and inverted in glasses of naphtha, and slowly admitted water to the amalgam at the bottom of the glass; but this precaution I soon found unnecessary, for the action of the water was not 30 intense but that the hydrogen gas could be wholly collected.

I shall give an account of the most accurate experiments made on the decomposition of water by the bases of potash and soda..

In an experiment on the basis of potash conducted with every attention that I could pay to the minutiæ of the operations, hydrogen gas, equal in volume to 298 grains of mercury, were disengaged by the action of .08 grains of the basis of potash which had been amalgamated with about three grains of mercury. The thermometer at the end of the process indicated a temperature of 56° Fahrenheit, and the barometer an atmospheric pressure equal to 29.6 inches.

Now this quantity of hydrogen * would require for its combustion a volume of oxygen gas about equal to that

* Researches Chem, and Phil. page 287,

occupied

occupied by 154.9 grains of mercury, which gives the weight of oxygen required to saturate the .08 grains of the basis of potash at the mean temperature and pressure nearly 0151 grains. And .08 .0151.0951.08:

100 84.1 nearly.

And according to these indications 100 parts of potash consist of about 84 basis and 16 oxygen..

In an experiment on the decomposition of water by the basis of soda, the mercury in the barometer standing at 30.4 inches, and in the thermometer at 52° Fahrenheit, the volume of hydrogen gas evolved by the action of .054 grains of basis equaled that of 326 grains of quicksilver. Now this at the mean temperature and pressure would require for its conversion into water, 0172 of oxygen, and .054+.0172=.0712: .054 :: 100: 76 nearly; and according to these indications 100 parts of soda consist of nearly 76 basis and 24 oxygen.

In another experiment, made with very great care,. .052 of the basis of soda were used; the mercury in the barometer was at 29.9 inches, and that in the thermometer at 58° Fahrenheit. The volume of hydrogen evolved was equal to that of 302 grains of mercury; which would demand for its saturation by combustion, at the mean temperature and pressure .01549 grains of oxygen; and 100 parts of soda, according to this proportion, would consist nearly of 77 basis, and 23 -oxygen.

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The experiments which have been just detailed, are those in which the largest quantities of materials were employed; I have compared their results, however, with the results of several others, in which the decomposition of water was performed with great care, but in which the proportion of the bases was still more minute: the VOL. XIII.-SECOND Series.

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