Page:Proceedings of the Royal Society of London Vol 1.djvu/494

Rh When the bulb of a thermometer, wrapped in ﬁne lint, has been dipped in the sulphureous liquor. if it be simply exposed to the air it sinks to about zero of Fahrenheit’s scale, although by a similar eva- poration of ether the cold produced is not below 20°.

If a thermometer, coated as before, and \vetted with the sulphuret, be placed in the receiver of an air-pump, a cold of 65° or 70° below 0° is easily obtained, by a vacuum which supports one fourth of an inch of mercury; and if the air-pump can exhaust as far as one eighth of an inch, the thermometer sinks to —81° or —82° in less than two minutes, even though the thermometer at the commencement of the experiment was as high as 70° above 0.

Hence the freezing of mercury is an experiment that may be per- formed at any time, and with no more apparatus than a common air- pump, and enough of the sulphuret to moisten the bulb of a theme. meter. Since sulphuric acid has no afﬁnity for the sulphuret, it has no effect in adding to the degree of cold produced upon the principle upon which that is employed by Mr. Leslie, excepting in so far as it removes any moisture that may be present in the air, and which in some measure impedes the process until it is converted into a heat frost, that may be seen adherent to the bulb of the thermo- meter.

From the strong evidence we have that a very large proportion of the world, as we now see it, has at some period been either in a state of actual combustion, or has felt the effects of heat, a high interest, says the author, attaches itself to volcanoes and their ejections, as partial instances of similar operations now going on.

In support of the igneous origin of primitive strata, it is observed, not only that no crystal imbedded in them contains Water, but that none of the materials of the strata contain water in any state.

The subject of the present experiments was thrown out in a liquid state from the cone of Vesuvius about the year 1792 or 1793.

It was of a dirty white colour, with streaks of yellow and green.

When heated, it fused without any loss of weight. When fused on charcoal, it was converted into sulphuret of potash.

In water it dissolved readily, leaving particles of specular iron and oxide of copper. Muriate of plaﬁna caused a copious precipitate from the solution, from the presence of potash. Nitrate of barytes aﬁorded an abundant precipitate of sulphate of barytes.

Sulphate of silver gave a curd-like precipitate, showing the presence of muriatic acid.

Prussiate of soda gave a red precipitate, consisting of prussiate of copper. Carbonate, or oxalate of soda or potash, occasioned no precipitation of any kind of earth; nor did any means employed detect the presence of boracic, or of any other acid, excepting the sulphuric and muxiatic.