The description thus given is with reference to moulding those bodies which cannot be so done by any other than an elastic mould; but glue moulds will be found greatly to facilitate casting in many departments, as a mould may be frequently taken by this method in two or three pieces, which would, on any other principle, require many.-Trans. Soc. Arts, xliv. 38.

8. Leslie's Apparatus for ascertaining the Specific Gravity of Powders*.-Relative to the instrument constructed lately by Mr. Leslie, for the purpose of ascertaining the density of powders, the Bulletin Universelle observes, that it is the same with the Stereometer of M. H. Say, the description of which with figures may be found in the 23rd volume of the Annales de Chimie, (1797,) at page 1. The instrument was made and often used, especially in ascertaining the specific gravity of gunpowder; it still exists in the collection of l'Ecole Polytechnique.-Bull. Univ. A. tome vi. p.

361.

9. Menstruum for Biting-in on Plates of soft Steel.-This menstruum, the result of the investigations of Mr. Humphrys, consists of a quarter of an ounce of corrosive sublimate powdered, and a quarter of an ounce of alum powdered, dissolved in half a pint of hot water. It must be allowed to cool before being used, and when on the plate, it is to be stirred continually with a camel's-hair brush, and the plate washed perfectly after each biting. As the acid, though clear at first, becomes turbid during its action on the steel, it may be prudent, in fine works, to throw away each portion of acid after it has been on the plate. The taste and experience of the artist must dictate the length of time he may leave it on his plate; delicate tints are obtained in about three minutes. The process of biting is much more difficult of performance on soft, than on hard, steel, perhaps in consequence of the proportion of carbon in the latter, which affects the state of the iron when taken into solution: for, by soft steel, engravers mean not a steel that has been heated and cooled slowly, in contradistinction to one that has been hardened, for they always work upon steel as soft as it can be rendered, without change of composition; but he understands a steel that has been decarbonised, and brought back towards the state of iron. The difficulties which have usually occurred with such partially-decarbonised steel are removed, according to the experience of the artists who have tried Mr. Humphry's menstruum, by its substitution for the solvents previously resorted to.-Trans. Soc. Arts, xliv. 53.

10. Etching on Ivory.-The usual mode of ornamenting ivory in black is to engrave the pattern or design, and to fill up the cavities thus produced with hard black varnish. The demand for

* See Quarterly Journal, xxi. 374.

ivory thus engraved is considerable. Mr. Cathery has much improved and simplified the process, by covering the ivory with engraver's varnish, and drawing the design with an etching needle; he then pours on a menstruum, composed of 120 grains of fine silver, dissolved in an ounce measure of nitric acid, and diluted with one quart of pure distilled water. After half an hour, more or less, according to the required depth of tint, the liquor is to be poured off, and the surface is to be washed with distilled water, and dried with blotting paper. It is then to be exposed to the light for an hour, after which the varnish may be removed by means of oil of turpentine. The design will now appear permanently impressed on the ivory, and of a black or blackish-brown colour, which will come to its full tint after exposure for a day or two to the light. Varieties of colour may be given by substituting the salt of gold, platina, copper, &c. for the solution of silver.-Trans. Soc. Arts, xliv. 57.

11. Method of Cutting Glass.-If a tube, a goblet, or other round glass body is to be cut, a line is to be marked with a gun-flint having a sharp angle, an agate, a diamond, or a file, exactly on the place where it is to be cut. A long thread, covered with sulphur, is then to be passed two or three times round the circular line, is to be inflamed, and burnt; when the glass is well heated, some drops of cold water are to be thrown on to it, when the pieces will separate in an exact manner, as if cut with scissors. It is by this means that glasses are cut circularly into thin bands, which may either be separated from, or repose upon, each other, at pleasure, in the manner of a spring.-Jour. de Connaissances usuelles, iv. p. 15.

12. Preservation of Skins.-I. Stegar, a tanner, at Tyman, in Hungary, uses with great advantage the pyroligneous acid, in preserving skins from putrefaction, and in recovering them when attacked. They are deprived of none of their useful qualities, if covered by means of a brush with the acid, which they absorb very readily.

13. Indian Method of Varnishing.The uncivilised Indians, called Andoquies, who live near the sources of the river Magdalena, in Columbia, South America, use a vegetable substance as a varnish, a specimen of which has been sent to the Society of Arts. When taken from the shrub on which it grows, it is kept in water to preserve it moist: when perfectly dry it is considered useless, as those who work it up have no means of reducing it again to a soft state. When about to be used, it is put into boiling water, to separate from it the oily matter it contains. When effectually freed from the oil, it is taken out, and the varnisher puts a small quantity into his mouth, and continues to chew it as he goes on with his work. After thus chewing a bit of the varnish for some

time, he takes it out, and draws and extends it between his hands till it becomes exceedingly thin, thinner, perhaps, than the finest paper. In this state it is laid on the article to be varnished, and to which it adheres. When used with gold and silver leaf, as is often the case, the gold or silver is placed between two folds of the varnish, and thus applied: the fold on the inside is to make the whole adhere, and that on the outside is to varnish and protect the gold and silver, which shine through, and produce a good effect. The varnish combines readily with various colouring substances, which the people there use with it.-Trans. Soc. Arts, xliv. 192.

II. CHEMICAL SCIENCE.

66

1. Heat evolved from Air by Compression.-By a mathematical investigation of the heat extricated from air, when it undergoes a given condensation, and by a reference to the experiments of Clement, Gay-Lussac, and others, Mr. Ivory finds, that the heat extricated from air, when it undergoes a given condensation, is equal to three-eighths of the diminution of temperature required to produce the same condensation, the pressure being constant." Air, under a constant pressure, diminishes 1-480th of its volume*, for every degree of depression on Fahrenheit's scale; and therefore one degree of heat will be extricated from air, when it undergoes a condensation equal to TT. If a mass of air were suddenly reduced to half its bulk, the heat evolved would be = 90°. -Phil. Mag. N. S. i. 89.

2. On the Action of a Moving Metallic Disc, upon a portion of a Voltaic Conductor.-Immediately after the highly interesting discovery made by M. Arago, relative to the effects produced reciprocally by magnets and metallic plates, when the one or the other were put into a state of motion, M. Ampère was led by his views of the nature of magnetism, to look for a similar effect, when the magnet was removed and replaced by a conducting wire formed into a helix, for when an electric current is sent through such a wire, it is found to possess all the properties of a magnet. A. double spiral was formed from wire, and delicately suspended above a horizontal disc of copper, to which a rotary motion was given by convenient apparatus, also of copper. The two extremities of the wire forming the helix were plunged into two circular cups, or troughs, filled with mercury, and placed in communication with the poles of a voltaic battery; a screen was placed between the copperplate and the suspended spiral. Immediately upon moving the plate, the spiral began to turn in the same direction, precisely like a magnetic bar, or like the assemblage of two vertical magnets attached to a horizontal lever. Ultimately the rotary movement became accelerated and continuous. Upon altering the direction

At 32° F.-ED.

of the motion in the disc, the motion of the spiral immediately changed, in all cases continuing the same as that of the plate. This satisfactory fact is a powerful addition to those by which M. Ampère supports his views of the nature of magnetism generally, and its origin in all cases from currents of electricity.—Bull. Phi. 1826, p. 134.

3. Influence of the Aurora Borealis on the Magnetic Needle.-A luminous arc produced by an aurora borealis was seen on the 29th of April, 1826, at Carlisle and in Roxburghshire. This phenomenon was not seen at Gosport, though the sky was very clear. At 7 h. 50' P.M. of the 29th April at Paris, the north point of the needle indicating diurnal variations was 4 to the east of its ordinary position; at half past eight o'clock it passed westward with a ready movement; at three-quarters past eleven o'clock it had returned within half a minute to the position it had at half-past eight. Long experience has taught me that these great oscillations, at hours when the needle is generally stationary, is an indication almost certain of the existence of an aurora borealis. M. Arago, the author of these observations, then ventures to announce, solely from the effects he has observed upon the magnetic needle, that brilliant aurora boreales will have been observed in some part in the north on the following days of the year 1826: the 16th of January, the 10th and 13th of February, the day of the 9th of March, the morning and evening of the 23rd of March, and the 29th of the same month, the 9th and 13th of April, the nights of the 17th and 18th of April, the 24th of the same month, &c.-Annales de Chimie, xxxiii. 421.

4. Electro-chemical Appearances.-M. Nobili has been induced to contract one of the poles of the voltaic pile in the manner first pointed out by Dr. Wollaston, namely, by inclosing a wire within a glass tube, and exposing only a sectional surface, and has observed the effects which occur when such a pole is used in the decomposition of various saline solutions, the other pole being a plate of metal, brought very near to it. The general results appear to be two in number. The first consists in the property remarked of certain electro-negative substances to attach themselves, in certain determinate circumstances, to the surface of those metals which are least oxidable, in thin regular layers, so as to present the beautiful phenomenon of coloured rings in a splendid manner. effect, it is supposed, may be applicable in the ornamental arts. The second is, that when electro-negative substances are not deposited in thin plates upon the metals, they generally attack their surfaces, not in an uniform manner, as might be supposed, but by a gradation of intensity from the centre, continued and decreasing, but at irregular intervals, following, as it were, a law analogous to that of interferences. The same phenomenon is observed in the attachment of electro-positive substances to the negative pole, namely, an alternation in the circles of oxide and of metal, M. Nobili then

This

inquires, whether it can be true that radiation of the electric currents is subject to a law of interference, and acknowledges, notwithstanding the alternations he has obtained, that new experiments are required.-Bib. Univ. xxxiii, 302.

5. Earthy Depositions from Water influenced by the Electricity of Metals in contact.-M. Dumas has noticed an interesting case of voltaic action, which has occurred with water contained in metallic tanks and tubes. The water from the springs in the neighbourhood of the Seine are strongly charged with carbonate of lime, held in solution by carbonic acid. When it is received and retained as before mentioned, it occasions incrustations, which, however, are not indifferent as to the places on which they occur, but are governed by the electrical relations of the metals forming the vessels. The Sévres porcelain works are supplied with water of this kind, which is received and retained in a leaden reservoir; the general internal surface of the lead presents scarcely a trace of deposit, but a thick coat has been formed on the lines of solder by which the plates of lead are joined. The incrustation is irregular, but evidently crystalline; it is slightly coloured by oxide of iron, and dissolves entirely, with effervescence, in nitric acid. A bar of iron used to raise a valve, and consequently plunged in the water, was covered with a layer five or six lines in thickness, the lead in the immediate neighbourhood being nearly free from the deposit.

In the tubes which conduct the water, the deposit occurs only at the soldered joints. The plumbers know this fact, and when the pipes appear to be stopped up, always go to these places. The copper cocks are also the localities of deposition.

Abundant proof was obtained that these effects were voltaic, by immersing simple combinations of metals into portions of the water; and M. Dumas proposes a remedy for the evil occasioned by the deposition, by causing it to take place in unimportant or accessible situations. For this purpose he considers the assemblage of tubes as an immense plate, and proposes to attach lateral tubes to it, at intervals from twenty to thirty feet; these are to be closed by metallic plugs, containing rods affixed to them projecting into the water, of such a nature as to become the negative part of the arrangement; all the depositions will then take place on these stoppers and rods, and none upon the lead. From the effects observed, it is concluded that cast-iron will well answer the purpose.-Annales de Chimie, xxxiii. 265.

6. Instance of a returning Stroke by Lightning.-The returning stroke of lightning is well known to be due to the restoration of the natural electric state, after it has been disturbed by induction, Thus if a person be brought into a highly electric and negative state by induction, from the approximation of a body highly charged positively, and then the latter be discharged by means having no connexion with the negatively electrified person, the negative state