be ultimately adopted for these purposes. There seem at present some difficulties as to the best mode of using this combustible; since by sudden exposure to an incandescent furnace it is apt to split or exfoliate into minute fragments, which choke up the draught of air, or are thrown out like dust by any rapid motion. Dr. Ure assigns as the cause of this, I believe truly, that being a bad conductor of heat, the superficial parts expand and break off from the cooler internal portions; the remedy for which appears to be some contrivance for gradually heating the coal before it comes into contact with the fire, and of supplying a constant current of hot air; these precautions are not required for common fires. Mr. Player has secured a patent for such a process, which is exhibited on the Thames in the steamer called the Anthracite, the action of which every one is disposed to praise, yet no one adopts: for this no reason appears but the difficulty of overcoming prejudices, or the fear of engaging in novelties in the first instance requiring some additional expenditure.

With regard to its application to domestic use it has many and forcible recommendations; it gives out a clear, steady and durable heat; requires but little attention when once lighted; and the absence of all annoyance from smoke, soot or dust, renders it very desirable for culinary purposes and for bedrooms; in the parlour it may be thought deficient in the bright and cheerful character which belongs to the Newcastle coal; besides which, as the anthracite never cakes, it requires no aid from the poker, the employment of which on the contrary extinguishes the fire, and therefore may be deemed objectionable.

Analysis of the vein of Anthracite coal called the Gwerdd (Green) vein from Coalbrook in Carmarthenshire near Pont y berem, in the vale of the Gwendraeth, the property of the Gwendraeth Anthracite Company; by Mons. Jac

quelain, of the Ecole des Arts at Paris.

One gramme of the coal reduces 33.3 grammes of lead, consequently the heating power may be thus estimated: 1 kilogramme is capable of raising 76.54 kilogrammes of water (quere from 32°) to the boiling point, or of evaporating 11.55 kilogrammes. All the samples of coal placed in my hands were of a brilliant black, very compact, and of a lamellar structure; the cross fracture rough and uneven; they do not soil the fingers, and break easily under the hammer; the hardness is nevertheless considerable, and it is difficult so to reduce it to powder as to destroy its brilliancy.

The double carbonate of lime and iron occurs between the laminæ of this coal, and sometimes agglomerations of carbonaceous matter possessing the appearance, lightness and friability of wood charcoal.

The specific gravity of this coal is 1.27; it burns in the furnace without flame; a small quantity reduced to powder consumes slowly without inflaming; ignited masses do not lose their form, but when separately exposed to the air become extinguished, whereas in mass the combustion succeeds well in the reverbatory furnace.

I incinerated some of this coal reduced to powder in a muffle furnace charged with the same coal, and beginning with a stratum of lighted charcoal: the combustion continued for five hours, while every part of the interior of the furnace was incandescent.

The residue of this incineration upon a small scale, consists of slightly ferruginous and calcareous eous ashes; that of combustion on the large scale is similar, but mixed with some small pieces of coal having suffered incipient exfoliation. The ready combustion in mass is undoubtedly to be attributed to a slight separation of the laminæ of the coal produced by the high temperature, and to the emission of a gas*.

The quantity of gas which this coal is capable of supplying in close vessels has been found to be 24 litres for 100 grammes of coal, equivalent to 240 litres for a kilogramme. It will be seen that these results approach those obtained on the large scale in gas-works, where that quantity yields 180, 200, and 250 litres of gas; unfortunately the gas produced from this anthracite does not give more light than pure hydrogen; it is now well known that illuminating power may be communicated to hydrogen gas by causing it to circulate in reservoirs

over the surface of oil of schist or of tar.

From what has been stated, it is evident that coal having a uniform character similar to that which I have analysed, would be much in demand on account of its remarkable purity, both for domestic consumption and for blast furnaces,

and especially for the latter, on account of the extremely high temperature it is capable of producing.

I repeat, that if this combustible prove homogeneous and of equal quality in every part of the deposit, the discovery is one of great importance for the reduction of ores and the quality of the resulting products.

Dr. Schafhaeutl of Munich, now or lately residing at Swansea, has analysed for the Kilgetty Company, two samples of the Pembrokeshire coal; the average specific gravity he states to be 1.413.

XXXI. On the Tension Spark from the Voltaic Battery. By ANDREW CROSSE, Esq. Communicated in a Letter to John P. Gassiot, F.R.S.

To the Editors of the Philosophical Magazine and Journal. GENTLEMEN,

THE inclosed communication from my friend Andrew Crosse, Esq., may perhaps be interesting to the readers of the Philosophical Magazine; the paper he alludes to is one I communicated to the Royal Society, and which was honoured by a place in their Transactions of this year.

I am, Gentlemen, yours, &c.

Clapham Common, Aug. 3, 1840.

MY DEAR SIR,

JOHN P. GASSIOT.

I return you my best thanks for your paper on the voltaic spark, &c.; I have read it with attention, and was much interested by its perusal, particularly by that part which relates to Zamboni's pile. I once had a cork ball kept vibrating between the poles of four columns of De Luc's pile, without cessation, for upwards of twelve years! Now for the possibi

lity of obtaining a spark between the poles of a voltaic battery before the circuit is completed. Were you to see the action of my unfinished water battery of 1626 pairs of zinc and copper cylinders, you would allow the question to be set at rest. I take a small glass stick, and tie on it, with waxed silk thread, very securely, two wires of platina, with the two extreme ends ready to be plunged into two cups of mercury connected with the opposite poles of the battery: the two other ends of the wires are brought to the distance of about Tooth of an inch from each other, as below.

AB, CD, two platina wires secured on the glass stick E, F, G, H at the parts E, F, G, H. The two nearest ends of the wires approach each other at B, C to about the distance of Tooth of an inch. I say about, for I have no instrument to measure it with accuracy, nor is it of any consequence, as the cells of that battery are not by any means so well insulated, as that the above distance should be taken as a test of intensity of the battery. The moment the connexion is made with the poles of the battery, a small stream of fire takes place at the interval between B and C, which I have kept up for many minutes, nor did it appear inclined to cease. experiment never fails, but with a much greater number of plates, each pair not being separately insulated, it would never succeed. To expect to produce a spark or visible current under similar circumstances with the above would be hopeless, except with a considerable number of pairs of plates, each pair being separately insulated. With 1200 pairs I have succeeded, and with 10,000 or 20,000 the distance at which it would strike would be very great, comparatively speaking.

This

I showed a friend the other day about twelve inches of iron chain illuminated pretty strongly by the passage of repeated shocks of my large electrical battery through it, charged by the water battery alone. The intensity was so great as to keep up a constant dance of pieces of silver-leaf between two plates connected with the opposite poles. The reason why Professor Daniell's water battery, which you employed in some of your experiments, failed, was first, that the cells were not separately insulated, and secondly, that they were too few in number. I presume it was the water battery which I once saw used at the Royal Institution, the intensity of which was very feeble.

I do wish you could manage to pay me a visit, and see the

action of my battery. I mean, as soon as I have time to add about 850 pairs of cylinders to it. Woe then to the unfortunate wretch who comes between the poles, when connected with the electrical battery!

P. S. Please to observe, that when I procured the stream of electricity in the interval between the platina wires, I used the water battery alone, without other apparatus, and not connected with the electrical or any other battery.

Broomfield, near Taunton, July 17, 1840.

XXX II. On the Process of Daguerreotype, and its application to taking Portraits from the Life. By JOHN WILLIAM DRAPER, M.D., Prof. Chemistry in the University of New York.

VERY soon after M. Daguerre's remarkable process for Photogenic Drawing was known in America, I made attempts to accomplish its application to the execution of portraits from the life. M. Arago had already stated, in his address to the Chamber of Deputies, that M. Daguerre expected, by a slight advance, to meet with success, but as yet no account has reached us of that object being attained.

More than one hundred instances are recorded in Berzelius's chemistry, in which the agency of light brings about changes in bodies; these are of all kinds: formations of new compounds, re-arrangements of elements already in union, changes of crystallographic character, decompositions, and mechanical modifications.

The process of the Daguerreotype is to expose a surface of pure silver to the action of the vapour of iodine, so as to give rise to a peculiar iodide of silver, which under certain circumstances is exceedingly sensitive to light. The different operations of polishing, washing with nitric acid, exposure to heat, &c., are only to offer a pure silver surface; the operation of hyposulphite of soda, and the process, which I shall presently describe, of galvanization, are to free the plate from its sensitive coating, and in no wise affect the depth of the shadows, as some of the French chemists at first supposed.

There is but one part of the Daguerreotype which does not yield to theory: on one point alone there is obscurity. Why does the vapour of mercury condense in a white form on those portions of the film of iodide, which have been exposed to the influence of light?-condense to an amount which is rigidly proportional to the quantity of incident light?

Even on this point there are facts which appear to have a bearing.

(a.) It has long been known, that if a piece of soapstone or