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Art. LXII.—Notes on the Formation and Constitution of Torbanite and similar Minerals.
[Read before the Wellington Philosophical Society, 29th August, 1874.]
In prosecuting experiments, previously detailed, upon the evolution of heat caused by mixing dry clay with various liquids, I noticed such an increase of temperature in the case of petroleum that I suspected an absorption of a portion of the matters dissolved in this liquid had occurred, and so was led to investigate the matter further, when the following results were obtained:—
| (1.) |
That our commercial kerosenes are nearly or quite decolorised by mixing them with dry clay, and our best native petroleum greatly modified. |
| (2.) |
That this process is very much quicker when the clay used has been dried at 100° or so C. |
| (3.) |
That in such a case the clay, if white, acquires a rose and afterwards a black colour, while its streak is light brown. |
| (4.) |
That torbanite has the same effect as clay. |
| (5.) |
That the coals I have examined, whether hydrous or anhydrous, do not appear to exercise any absorbent action upon the petroleum oils. |
| (6.) |
That the same is true of diatomaceous earth (dry), carbonate of lime, and gypsum, hydrous or anhydrous, also pumice-stone and pipe-clay (ignited). |
| (7.) |
That kerosene which has been completely decolorised by clay, when heated to 100° to 150° C., blackens clay, but has no such effect upon other porous substances, as gypsum, or prepared silica. |
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| (8.) |
That clay is similarly affected by hot paraffin. |
| (9.) |
That clay can readily be charged with some of the constituents of petroleum, to such an extent as to have almost the consistence as well as the appearance of torbanite. |
These results have, I believe, an important bearing upon our present theories as to the formation and constitution of the valuable mineral torbanite. As to the formation of this mineral, it plainly appears from them that clay strata can abstract the colouring matter of petroleum. If this process is carried on to a small extent we have only a feebly bituminous clay, but if carried on till the clay is saturated, or nearly so, we have a mineral which I believe has exactly the constitution of torbanite. During the formation of this mineral the petroleum passing through it would be purified to a greater or lesser extent.
From what has been already stated, I feel sure the absorption is not of a mechanical but of a chemical nature, and this brings me to the next point, that is, the nature of the mineral in question, torbanite or bog-head coal.
As to its constitution, this mineral is associated with the amber group in our best mineralogical works, and the earthy matter is thrown out of the formula. Now, this earthy matter is within small limits uniform in amount in the case of all the samples of this mineral yet analysed, being from nineteen to twenty-six per cent., and it is essentially silicate of alumina, that is anhydrous clay.
I consider, therefore, the ash of this mineral is not an accidental element as now stated, but is an essential part of it,—that, in fact, torbanite is a combination of a bituminous kind of substance with clay, the water of the clay being either substituted by it or a bitumino-silicate of alumina formed, which substance may have no affinity or but a very slight one for water.
The colouring matters for petroleum and kerosene are in general terms described as of a bituminous nature—bnt whether bitumen itself is actually or universally present in them has not yet been demonstrated. However, these colouring matters are certainly oxidized hydrocarbons, and so class with bitumen and the combustible part of torbanite.
Being thus oxidized hydrocarbons they can hardly fail to be of an acidic nature, and so the statement as to their capability to chemically combine with clays as shown, is one which a consideration of the basic nature of clay will, I think, greatly predispose us to admit as a correct one.
In conclusion, these results tend to indicate—
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(1.) A cheap and expeditious method for purifying our coloured kerosenes, one in which there need hardly be any waste.
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(2.) That by using pure clay useful pigments may perhaps be obtained in this manner.
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(3.) That torbanite is not coal, but a chemical combination of an acid hydrocarbon with silicate of alumina.
(In this assumption I accept for the present the popular opinion which maintains the ash of coal itself to be an accidental element.)
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(4.) That our present formula for torbanite requires amendment so as to include earthy matters.
I will only add that, judging from the basic nature of alumina and the refusal of silica in any form to combine to a notable extent with any of the constituents of petroleum, it appears most likely it is the alumina of the earthy matters of torbanite to which the retention of its combustible part is due. This matter, and the possibility or otherwise of substituting compounds of tin, iron, copper, etc., for that of alumina as absorbents of the substances named, is now engaging my attention, and so I trust to be able to give information upon these points at an early date.