performed, together with a drawing of the pyrometer, in order that it may be the more easy to judge of what reliance may be put in the accuracy of the results.

II. CHEMISTRY.-MINERALOGY.

Table of the Proportions of anhydrous acid in acetic acid of every degree of concentration between pure water and the hydrated acetic acid, compared with the specific gravities, water at 59° Fahr. being taken at unity. Founded on Experiments, by ADAM VAN DER TOORN.

Account of some Experiments on the Electricity of the Copper
Vein in Huel Jewel Mine. By ROBERT W. Fox.

The author transmitted a section of the deepest part of the mine, with a description of the manner in which he conducted the experiments on its electricity.

Huel Jewel. Deepest workings on South or Main Lode, which underlies about 23° towards the North.

Black and vitreous Copper in the Vein, with some yellow Sulphuret intermixed.

The vein consists of black and vitreous copper above, and below, the yellow sulphuret of copper. Their boundaries are shown by the dotted lines.

A represents the observed station in a level 98 fathoms under the surface.

B, C, D, E, and F, show the points of contact where the metallic plates or copper wires were pressed against the vein, mostly by means of a wooden prop; and the dotted lines represent the copper wires employed.

Copper and zinc plates were alternately, or rather successively, used at each of the points of contact with the vein, except at D; but these changes of metal did not affect the character or direction of the electricity, nor did the contact of points only with the ore do so. But in all cases the easterly wires were positive with respect to the westerly ones. These experiments were made in order to prove that the electrical action is derived from the vein, and that it is not in any degree excited by the mere contact of the metal with the ore, as some have surmised.

In order to obtain some idea of the electric energy of the vein, the author placed a galvanic trough as in the circuit, at m, and caused it to act with the electricity of the vein, and also against it. In the former case, the deflections of the needle were considerably increased; and in the latter, when the electricity produced by the galvanic apparatus was opposed to that of the vein, the positive electricity from C was reversed, the galvanometer giving evidence of a slight negative action in that direction. The electricity from D, however, was only just neutralized, and that from E was merely diminished in intensity, the deflection of the needle being in the same direction, and equal to about 40°, from the magnetic meridian, instead of 100° at least, produced by the vein alone.

The galvanic apparatus consisted of a plate of copper, and another of zinc, plunged into strong brine, to which some sulphuric acid was added, and each plate exposed about 180 square inches to the action of the liquid. The voltaic activity was much diminished before the completion of the experiments; but even at the last, when the wires of the apparatus were applied to the galvanometer without the intervention of the vein, and the extensive circuit and comparatively imperfect contacts which it involved, a violent agitation and rapid rotation of the needle were produced.

These experiments afford strong evidence of the energy of the electricity of the vein; and this method may become useful to the practical miner, in helping him to appreciate the value of his discoveries, and enabling him to ascertain whether the ores in distant parts of a vein are connected or insulated, or whether what appear to be parallel veins are really so, or ramifications

of the same vein. Galena, and copper, and iron pyrites are the only substances usually met with in the Cornish mines which are capable of conducting voltaic electricity; and as iron pyrites is much more generally found in insulated masses than the other two, the test here suggested may be employed with a considerable degree of confidence on many occasions.

It was in Huel Jewel, and more than four years ago, that the author first obtained electro-magnetic results. The workings have been so much extended since, that the last experiments were made 60 fathoms deeper, and at least 80 fathoms further towards the east, than the first; and it is satisfactory to find that the direction of the electricity remains unchanged, viz. positive from the east. The temperature at the bottom level of the mine, 38 fathoms under the surface, was then 59°, and it is now, at the depth of 108 fathoms, 70°. The author has observed that when the sulphuret of copper or of lead is heated, or even slightly warmed, it becomes positively electrical, and yet the deepest parts of the veins of those ores, although warmer than nearer the surface, appear generally to be negative.

Notice respecting a remarkable Specimen of Amber. By Sir DAVID BREWSTER, F.R.S.

This specimen of amber was brought from India by Mr. Swinton, and was found in the kingdom of Ava. Its size is nearly equal to that of a child's head, and its general aspect and physical properties, seem to differ considerably from the ordinary specimens of amber. The remarkable fact, however, which distinguishes it from all specimens of amber which the author has seen or read of, is that it is intersected in various directions by thin veins of a crystallized mineral substance. These veins, which cross one another, are sometimes as thin as a sheet of paper, and in other places about the twentieth of an inch thick. In order to determine the nature of the mineral, he extracted a portion of the thickest vein; and having obtained, by cleavage, a small rhomb, succeeded in measuring the inclination of its planes, and found it to be a carbonate of lime. The specimen, however, did not enable him to ascertain whether the angle was that of the pure carbonate of lime, or that of carbonate of lime and magnesia.

At the next meeting of the Association, the author hoped to be able to bring forward a detailed account of this curious specimen, and to exhibit it to the Section; but he considered the single fact which he had now mentioned as calculated to throw so much light on the origin of amber, that he trusted it

would induce those who are in possession of specimens to examine them with attention, and especially in reference to empty or filled cavities, and to veins or portions of foreign matter which may exist in the mass.

Remarks on the value of Optical Characters in the discrimination of Mineral Species. By Sir DAVID BREWSTter.

If minerals were all formed from solutions containing the same ingredients, having the same temperature, and crystallizing in perfect tranquillity, the differences recognised by the chemist, the crystallographer, and the optical observer would have no existence; but as this hypothetical state of the mineral, when in a state of fluidity or solution, is inadmissible, we must consider minerals as having been formed under the influence of many disturbing causes. In order to illustrate this remark, the author takes the case of chabasie, which he regards as a congeries of several substances, formed in succession round a central rhomb of the same mineral in a perfect state. The central rhomb has a certain degree of double refraction, which is equal in all parallel directions; but there is another rhomb formed round it which has a less double refraction, and each successive rhomb has its double refraction successively diminishing till it disappears altogether, at which period the form of the crystal would be a cube. Beyond this neutral line an opposite kind of double refraction appears, corresponding to a new series of rhombs, deviating more and more from the cubical structure.

Now it is very obvious that these changes may have, or rather must have, taken place, either from some agitation in the fluid which prevented its particles from assuming the perfect type of the mineral, or from the addition or abstraction of some of the ingredients of which the central rhomb was composed.

If a crystallographer, therefore, were to examine such a mineral, he would report to us only the condition of the outer rhomb, while the chemist would detail to us the elements which form the whole compound mass. The optical observer, however, is alone admitted into the secret, and his results are infallible. The changes which take place in the optical characters of minerals by heat, do not in the least affect their value, any more than similar changes affect the ordinary characters which are employed by mineralogists. The specific gravity of bodies varies also with heat, and probably the hardness also of the softer minerals; and it is well known that changes of temperature not very great may drive off the more valuable ingredients of minerals, and thus prevent the chemist from obtaining their actual composition.