« VorigeDoorgaan »
XXX. On a saline Substance from Mount Vesuvius. By James
Smithson, Esq. F. R. S.
Read July 8, 1813.
It has very long appeared to me, that when the earth is considered with attention, innumerable circumstances are perceived, which cannot but lead to the belief, that it has once been in a state of general conflagration. The existence in the skies of planetary bodies, which seem to be actually burning, and the appearances of original fire discernible on our globe, I have conceived to be mutually corroborative of each other; and at the time when no answers could be given to the most essential objections to the hypothesis, the mass of facts in favour of it fully justified, I thought, the inference that our habitation is an extinct comet or sun.
The mighty difficulties which formerly assailed this opinion, great modern discoveries have dissipated. Acquainted now, that the bases of alkalies and earths are metals, eminently oxydable, we are no longer embarrassed either for the pabulum of the inflammation, or to account for the products of it.
In the primitive strata, we behold the result of the combustion. In them we see the oxyd collected on the surface of the calcining mass, first melted by the heat, then by its increase arresting farther combination, and extinguishing the fires which had generated it, and in fine become solid and crystallized over the metallic ball.
Every thing tells that a large body of combustible matter still remains enclosed within this stony envelope, and of which volcanic eruptions are partial and sınall accensions.
Under this point of view, an high interest attaches itself to volcanoes, and their ejections. They cease to be local phenomena; they become principal elements in the history of our globe; they connect its present with its former condition ; and we have good grounds for supposing, that in their flames are to be read its future destinies.
In support of the igneous origin, here attributed to the primitive strata, I will observe, that not only no crystal imbedded in them, such as quartz, garnet, tourmaline, &c. has ever been seen enclosing drops of water ; but that none of the materials of these strata contain water in any state.
a. The present saline substance was sent to me from Naples to Florence, where I was, in May 1794, with a request to ascertain its nature. The general examination which I then made of it, shewed it to be principally what was at that time called vitriolated tartar, and it was in consequence mentioned as such in an Italian publication soon after. But as this denomination, surprising at that period, was not supported by the relation of any experiments, or the citation of any authority, no attention was paid to it; and the existence of this species of salt, native in the earth, has not been admitted by mineralogists, no mention being made of it, I believe, in any mineralogical work published since.
b. I was informed by letter, that it had “ flowed out liquid from a small aperture in the cone of Vesuvius,” and which I apprehend to have happened in 1799 or 1793.
c. The masses of this salt are perfectly irregular, their texture compact, their colour a clouded mixture of white, of the green of copper, and of a rusty yellow, and in some places are specks and streaks of black.
d. A fragment melted on the charcoal at the blow-pipe formed hepar sulphuris.
e. A piece weighing 9,5 grains was so strongly heated in a platina crucible, that it melted and flowed level over the bottom of it, but did not lose the least weight.
f. Not the slightest fume could be perceived on holding a glass tube wetted with marine acid over some of this salt, while triturating in a mortar with liquid potash; but a similar mixture being made in a bottle, and which was immediately closed with a cork, to which was fixed a bit of reddered litmus paper, the blue colour of the paper was restored.
g. Being dissolved in water, there was a small sandy residue, which consisted of green particles of a cupreous nature, of a yellow ochraceous powder, and of minute crystals of a metallic aspect of red oxyd of iron, by which the black spots in the mass had been occasioned.* Mr. KLAPROTH found a similar adınixture in muriate of soda from Vesuvius, t
h. The solution had a feeble green tint. It did not alter blue or reddened turnsol paper.
i. Prussiate of soda-and-iron threw down a small quantity of red prussiate of copper from it. Liver of sulphur and tincture of galls likewise caused very small precipitations.
• What mineralogists denominate speculary iron ore, Fer oligiste of Mr. Haüy, appears to be merely red oxyd of iron in crystals; red hematite the same substance in the state of stalactite ; and red ochres the same in a pulverulent form. The bematites which afford a yellow powder are hydrates of iron.
+ Essays, Vol. II. p. 67, Eng. Trans.
j. Carbonate of soda, and oxalate of potash, and solutions of magnesia, clay, copper, iron, and zinc, either had no effects, or extremely slight ones.
k. Solution of sulphate of silver produced a white curd-like precipitate. 9,35 grains of this salt (the weight of the insoluble matter being deducted) afforded 1,05 grains of slightly melted muriate, or chloride, of silver. This precipitate was equally produced after the salt had been made strongly red hot, so that it was not owing to a portion of sal ammoniac.
1. Tartaric acid, and muriate of platinum, occasioned the precipitates in its solution which indicate potash.
. m. Nitrate of lime did not form any immediate precipitate in a dilute solution of it; but in a short time, numerous minute prismatic crystals of hydrate of sulphate of lime were generated.
n. Nitrate of barytes poured into a solution containing 9,8 grains of this salt afforded a precipitate, which after being ignited weighed 12,3 grains. The filtered solution crystallized entirely into nitrate of potash mixed with a few rhomboides of nitrate of soda.
0. Some of this salt finely pulverized was treated with alcohol. This alcohol on exhaling left a number of minute cubic crystals, which proved, by the test of nitric acid, to be muriate of soda. Prussiate of soda-and-iron caused a red precipitate of prussiate of copper in this alcoholic solution.
p. The solution of this salt afforded, by crystallization, sulphate of potash in its usual forms, and some prismatic crystals of hydrate of sulphate of soda.
q. To discover what had occasioned the precipitate with galls, (i) since copper has not this quality, a portion of this
salt, which had been recovered by evaporation from a filtered solution of it, was made red hot in a platina crucible, On extraction of the saline part by water, a very small quantity of a black powder was obtained. Ammonia dissolved only part of it, which was copper. The rest being digested with muriatic acid, and prussiate of soda-and-iron added, a fine Prussian blue was formed.
r. From several of the foregoing experiments, it appeared that no sensible quantity of any of the mineral acids, besides the sulphuric and muriatic, existed in combination with alkali in this volcanic salt. But Mr. TENNANT, whose many and
, highly important discoveries have so greatly contributed to the progress of chemical science, having detected disengaged boracic acid amongst the volcanic productions of the Lipari islands, and suggested that it might be a more general product of volcanoes than had been suspected, * it became important to ascertain whether the presence of any in this salt proved Vesuvius likewise to be a source of this acid. Alcohol heated on a portion of it in fine powder, and then burned on it, did not however shew the least green hue in its flame.
s. To ascertain the proportions of the ingredients of this saline substance, the following experiments were made:
10 grains of sulphate of potash of the shops were dissolved in 200 grains of water, and an excess of muriate of platina added. The precipitate edulcorated with 100 grains of water, and dried on a water bath, weighed 24,1 grains.
10 grains of the saline part of the native salt, treated precisely in every respect in the same way, afforded 17,2 grains. of precipitated muriate of platina-and-potash.
* Trans. of the Geolog. Soc..