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The equation of the tangent circle is therefore (x — AO)2+(y—B0)2=C202;

or reducing,

x2+ y2 —1—20(Ax+By−▼)=0;

and recollecting that Ax+By-v=0 is the equation of the axis of similitude, the equation shows that the axis of similitude is a common chord or radical axis of the orthotomic circle and the two tangent circles.

2 Stone Buildings, W. C. May 15, 1857.

LXVIII. Notes on Mineralogy.-No. V. On Hypostilbite and Stilbite. By the Rev. SAMUEL HAUGHTON, M.A., Fellow of Trinity College, and Professor of Geology in the University of Dublin*.

IN

N the twelfth volume of the Philosophical Magazine, p. 406, an analysis is published of a mineral allied to stilbite, by Mr. J. W. Mallet, and labelled hypostilbite by the person from whom he received it.

In the same volume, p. 552, this mineral is pronounced to be Laumonite by Dr. Heddle, who disposes of the label hypostilbite by means of the hypothesis, that "the christening may be explained by the ignorance of some unprincipled dealer resorting to a rare title in order to get rid of a superabundance of an insignificant-looking substance."

From the description given by Mr. Mallet and Dr. Heddle of the mineral, I have no doubt of its being the same as a mineral which has been some time in my possession, from the Isle of Skye; and as I find in my note-book the details of an accurate analysis made of it some years ago, I believe it is worth while to publish this analysis, as I entertain no doubt myself but that this mineral is identical with the hypostilbite of Beudant.

Analysis of Isle of Skye Mineral.

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I place in comparison with the foregoing analysis of the mi

* Communicated by the Author,

neral from the Isle of Skye, Beudant's analysis of hypostilbite from Faroe.

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This analysis agrees with Beudant's and my own, except as to the quantity of water present, and I think it would be very difficult to make a satisfactory mineralogical formula from any of the analyses. Hypostilbite is not well established as a distinct mineral, and should be considered as an altered form of stilbite.

I shall conclude this note by adding an analysis of some fine crystals of stilbite from the Nerbudda Valley, Hindostan, recently sent home by Mr. Jacob, C.E.

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This leads to the well-known formula for stilbite, which may be considered as a Hydrated Lime Orthoclase,

CaO, SiO3 + Al2 O3, 3SiO3+6HO.

If we are to consider hypostilbite as a distinct mineral, it should be regarded as a Hydrated Lime Oligoclase, with the formula CaO, SiO3 + Al°O®, 2SiO3+5HO

LXIX. Proceedings of Learned Societies.

ROYAL SOCIETY.

[Continued from p. 461.]

June 19, 1856.-The Lord Wrottesley, President, in the Chair. THE following communication was read :—

"On the Aurora." By Reuben Phillips, Esq.

In this paper the author enters into various speculations as to the formation and motion of auroral arches. Since it has been found by experiment that the maximum length of the voltaic arc with a given battery is nearly the same in atmospheric air and in highly rarefied air, forming a very perfect vacuum, the author conceives that a streamer begins as a disruptive discharge of finite and very moderate length, (the maximum length very nearly of a continuous discharge,) which starts upwards from the auroral arch, which he regards as the discharging train. If this first portion be not parallel to the dipping-needle, it is moved laterally by virtue of the earth's magnetism, and thus wrenched, as it were, from the spot where it was formed, and extinguished. If, however, the discharge, or any portion of it, be parallel to the dipping-needle, it is not influenced by the earth's magnetism, and remains. To this first length another length may be added by a similar process, and so on, these successive lengths being all parallel to the direction of the first, since otherwise the streamer would be torn asunder by the lateral motion resulting from the earth's magnetism. Thus a straight streamer extends upwards in a direction parallel to the dipping-needle.

If, from some increase in the power of conduction of the arch, the base of the streamer be not necessarily confined to a single spot, then a streamer may be formed which is somewhat inclined to the dippingneedle; but the consecutive elements of such a streamer must be in the same direction, otherwise they would have different lateral motions, the streamer would be divided, and the discharge would cease. The streamer, as a whole, will move from east to west, or from west to east, according to circumstances. Those streamers which would tend to move north or south cannot exist, because their bases would be severed from the auroral arch.

If the discharge take place in air not so very highly rarefied, so that the disruptive discharge is not quite of its maximum length, consecutive elements need not be quite in the same direction in order that the streamer may be unbroken, and thus curved streamers may be formed. It is stated by M. Biot that such have sometimes been observed.

The author then enters into some speculations as to the nature of the auroral arch, which he conceives to consist of nebulous matter highly charged with electricity, and accounts, according to his views, for the motion of such arches from the pole towards the equator.

The remainder of the paper is occupied with speculations as to the nature of fire-ball lightning, and other subjects relating to ordinary electricity.

"Chemical Examination of Burmese Naphtha, or Rangoon Tar." By Warren De la Rue, Ph.D., F.R.S., and Hugo Müller, Ph.D.* In several localities of the kingdom of Burmah, there emanates from the soil in considerable quantity a peculiar oleaginous substance, which is employed for a variety of purposes, but chiefly as a lampfuel and as an unguent, by the natives, and exported in moderate quantities under the name of Burmese naphtha, or Rangoon tar.

It is obtained by sinking wells of about 60 feet in depth, in which the liquid is collected by the miner as it oozes from the soil.

At the common temperature this substance has the consistence of goose-fat; it is lighter than water, has usually a greenish-brown colour, and possesses a slight odour, peculiar, but not disagreeable. It consists almost entirely of volatile constituents.

Burmese naphtha has already attracted the attention of other chemists; at present we refrain from entering into a discussion of their results, since it is our intention to give a full history of this remarkable natural product when, after the completion of our experiments, we shall have the honour of submitting to the Royal Society a detailed account of our investigation. The object of the present communication is to trace a mere outline of the results at which we have arrived up to this moment.

The circumstances under which petroleum-for this is the collective term which comprehends a great variety of oily emanations similar to Burmese naphtha-occurs in nature, all tend to prove that these substances are the products of a slow destructive distillation of the residuary matter of a primeval creation: this being admitted, the idea naturally suggested itself of examining this substance in comparison with the products of artificial destructive distillation.

With this view, one of ust was induced to procure, through the intervention of a friend, several tons of Rangoon tar, which was carefully collected at the source, and transmitted to Europe in well-secured vessels. Our experience in the course of this inquiry, has shown that this quantity, large as it may appear, was by no means too ample a supply. Burmese naphtha contains indeed so great a variety of substances, and some of them in so exceedingly minute a proportion, that even the large amount of material at our disposal was insufficient for the complete examination of several constituents, the presence of which we had succeeded in establishing beyond a doubt. As an example, we may state that Burmese naphtha contains small quantities of organic bases, the study of which we were compelled to postpone to a later period, when an additional quantity of material, which is now on its way to Europe, will have come to hand.

We have already mentioned that Rangoon tar is almost entirely volatile, and preliminary experiments proved to us that the distillation could be effected most conveniently, and with less danger of obtaining products of decomposition, in a current of steam; first of a temperature of 100° C. (212° F.), and subsequently of steam super*This paper was received during the Recess, and printed in No. 22 of the 'Proceedings.'

+ Warren De la Rue.

heated by passing, before it entered the still, through a system of pipes the temperature of which could be regulated. Treated in this way, it furnishes 96 per cent. of volatile products, fluid and solid.

Steam of 100° C. (212° F.) carries over 11 per cent. of a volatile oil perfectly free from solid hydrocarbons, which at that temperature are entirely retained in the distillatory apparatus. Between the temperatures of 110° and 145° C. (230°-293° F.), 10 per cent. of a further distillate is obtained, which is almost free from solid hydrocarbons. The temperature may be raised to 160° C. (320° F.) without materially augmenting this per-centage; but on gradually increasing the temperature of the steam to the fusion-point of lead, the operation yields 20 additional per cent. of distillate, which retains its fluidity at 0° C. (32° F.), notwithstanding the presence in it of an appreciable quantity of solid matter. At this stage of the process the products of distillation begin to solidify on cooling, and about 31 per cent. of a crystalline material is obtained sufficiently consistent to be submitted to pressure. After this the consistence of the products of distillation begins to diminish; and whilst the temperature of the steam is considerably raised, 21 per cent. of a mixture of solids and liquids distil, the latter predominating especially as the operation proceeds.

In the last stage of the process the distillate completely changes its character, becoming very dark in colour, of a pitch-like consistence, and exhibiting scarcely an indication of the presence of crystalline matter. When this product, which amounts to about 3 per cent., has passed over, there remains in the still a coke-like mass, which contains a small quantity of earthy impurities.

Although there is a considerable difference between the specific gravities of the first and last fractions of the distillates, all the products of distillation, like the original oil, are lighter than water, and could be separated therefore by means of the well-known apparatus (called a Florentine flask) employed in the distillation of essential oils.

By exposing the distillates obtained beyond the temperature of 145° C. (293° F.) to a freezing mixture, nearly all the crystalline matter solidified, and became removeable by means of filtration and pressure. It was thus ascertained that Rangoon tar contains from 10 to 11 per cent. of solid constituents (paraffine).

Solid Constituents.

The solid product, when removed from the fluid hydrocarbons, still retains a portion of the latter with much obstinacy; in order to purify the solid, it has to be subjected to the action of boiling concentrated sulphuric acid, and to be subsequently washed, first with an alkaline solution, then with water. On redistillation, the paraffine is obtained quite white, but even now it still retains some fluid hydrocarbons which have resisted the action of the sulphuric acid; the greater part can be removed by pressure between folds of cloth in a powerful hydraulic press and subsequent exposure for some months to the air, in which the fluids gradually disperse. By fractional crystallization from hot alcohol, we have been enabled to separate the

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