The

Italians have lately polished the surface of many figures they are accustomed to make, particularly the phrenological heads sold in the shops. reason of this effect must be evident to the chemist. The soap is decomposed by the plaster, the alkali of the soap is taken up by the sulphuric acid of the plaster, and the other constituent of the soap, namely, grease, is set at liberty, and remains as a glossy coat upon the surface. If it be desired to bronze a plaster figure, or medallion, paint it over with a mixture of Indian ink, indigo, and gamboge, or, still better, Indian yellow; so as to be of a dark and uniform olive color. Touch the more prominent parts with bronze powder, and varnish the whole over carefully, so as not to disturb the powder, with a weak solution of dragon's blood, dissolved in spirits of wine, and if well done they will appear as fine as any of the bronze medals of antiquity, though not so clear in their details; nor, (owing to their coat of color,) so sharp as medallions made of sulphur, afterwards to be described.

If plaster is at any time to be cast out of a plaster mould, the latter must be well greased before using, or if the moulds have been previously boiled in wax and grease, as recommended by some persons, or washed over with this mixture in a boiling state, oiling will alone be necessary. A very thick solution of soap will answer to separate the two surfaces. This is used by modellers.

(Continued on page 239.)

RAILWAYS.

(Resumed from page 198, and concluded.) Curvatures in the Road.-The curvatures of the railroad present some obstructions, since the axles of the car and waggons being usually fixed firmly to the frames, every bend of the tracks must evidently cause some lateral rubbing, or pressure of the wheels upon the rails, which will occasion an increased friction. If the wheels are fixed to the axles, so that both must revolve together, according to the mode of construction hitherto most usually adopted, in passing a curve, the wheel that moves on the outside or longest rail must be slided over whatever distance it exceeds the length of the other rail, in case both wheels roll on rims of the same diameter. This is an obstruction presented by almost every railroad, since it is rarely practicable to make such a road straight. The curvatures of some roads are of a radius of only 300 and even 250 feet. The consequence was that the carriages heretofore in use were obstructed, not only by the rubbing of the surfaces of the wheels upon the rails, already mentioned, but also by the friction of the flange of the wheel against the side of the rail. This difficulty has, however, been in a great measure remedied by an improvement made in the form of the rim of the wheel. The part on which this rim ordinarily rolls on the rail, is made cylindrical, this being the form of bearing evidently the least injurious to the road, as the weight resting perpendicularly upon the rails has no tendency to displace them or their supports. But between this ordinary bearing and the flange, a distance of about one inch in a wheel of thirty inches in diameter the rim was made conical, rising towards the flange one sixth of an inch, and thus gradually increasing in diameter. Wherever the road bends, the wheel, rolling on the exterior, and, in such case longer track, will, in consequence of the tendency of the carriage to move in a right line, be carried up a little on the rail, so as

to bear upon the conical part of the rim, which gives a bearing circumference of the wheel on that side greater than that of the wheel on the opposite end of the same axle. The tendency, accordingly, is to keep the car in the centre of the tracks, by producing a curvilinear motion in the waggon, exactly corresponding to the curve of the road. In the report made by Mr. Knight (of the United States of America), in 1830, he says that a car, with wheels such as those already described, was run upon a part of the Baltimore and Ohio railroad, where the greatest curvatures were of a radius of 400 feet, at the rate of fifteen miles per hour. In his report of October 1, 1831, Mr. Knight says that the additional friction on such a curve, above that on a straight road, is 1 in 1418, equal to 3.72 feet in a mile, with Winan's car, and in 1 356 equal to 14.83 feet in a mile, with another car. If the diameter of the wheel is increased, that of the conical part of the rim should be increased also, making the rise of the conical part between the flange and the cylindrical part (as Mr. Knight estimates in his report of February, 1830), one fifth of an inch in a wheel of three feet diameter, and one fourth of an inch in a wheel of four feet diameter. In his report of October 1, 1831, he says he had changed the ratio of the conical part of the rim, on wheels of the same size, from that of one to six, to that of one to five, and had increased the length of the conical part to 1 3-16ths of an inch and that he thinks the form of the rim was thereby improved. In the same report, Mr. Knight describes a method of turning a very short curve of a quadrant of a circle on a radius of sixty feet, by making a plate with a groove for the flange of the wheel on the longer track to run in; thus, in this case, making the difference of the rolling circumference of the wheels correspond to that of the two tracks. This plan was adopted for the purpose of turning corners or streets in towns, and, from experiments that have been made, promises to be successful.

:

If, for

Inclined Planes.-Where the inclination of the road is greater than that for which the ordinary power is calculated, the ascent must be effected by means of an additional power, the amount of which can be readily computed, since, in these parts, no additional friction of the cars or wheels is to be provided for, and only the additional resistance arising from gravity is to be overcome. instance, the additional inclination is one in ninetysix, or fifty-five feet in a mile, the additional power must be to the weight as one to ninety-six, or as fifty-five to the number of fect in a mile, namely, 5280. In descending planes, so much inclined that the gravity would move the carriages too rapidly for safety, the velocity is checked by means of a break, which consists of a piece of wood of the same curvature as the rim of a set of the wheels, upon which the break is pressed by means of a lever, so adjusted as to be within reach of the conductor, in his position on the carriage.

Power.-Gravity, horse power, and steam power have been used on railroads. Where the road is sufficiently and uniformly descending in one direction, gravity may be relied upon as a motive power in that direction; but on railroads generally, some other power must be resorted to in each direction. At the time of the construction of the Livepool and Manchester railway, much discussion took place, as to the expediency of using stationary or locomotive steam-engines. The result of the deliberations was, that if locomotives could be con

structed within certain conditions as to weight and speed, they would be preferable. The director accordingly offered a premium for the construction of such a locomotive, as should perform according to the conditions prescribed. At the celebrated trial on that road in October, 1829, of which Mr, Wood gives a particular account in the edition of 1831 of his work on railroads, the locomotive, called the Rocket,constructed upon the plan of Mr. Robert Stevenson, was found to come within the proposed conditions, and accordingly the decision, in respect to that road, was in favor of locomotives. The opinion in favor of this kind of power of road, of which the inclination does not exceed about thirty feet in a mile, has become pretty fully established. Stationary power can be used to advantage only on lines of very great transportation, as the expense is necessarily very great, and almost the same, whether the transportation be greater or less. Another objection to the use of stationary power is, that its interruption, in any part, breaks up the line for the time, which is not necessarily the case with a locomotive. The alternative, accordingly, is between the use of locomotive steam engines or horses, and the choice must be determined by the particular circumstances of the line of transportation. The advantages of this species of road are illustrated by the action of a horse upon it, compared with his performance upon the best turnpike, being as Mr. Wood assumes in one of his estimates, in the proportion of 7.5 to 1; thus enabling us to dispense with thirteen out of fifteen horses required for transportation on the best common roads. horse's power of draught is much the greatest at a low rate of speed, since the more rapid the velocity the greater proportion of his muscular exertion is required to transport his own weight. But it is ascertained, on the Baltimore and Ohio railroad that a speed of ten miles an hour may be kept up by horses travelling stages of six miles each, which would perform the whole distance between Baltimore and the Ohio river in thirty-six hours. The whole expense of transportation by horse power, including cars, drivers, and every expense except repairs of the road, on the same railroad, from January to September, 1831, amounted to about one third of the gross tolls received; and this expense, it was calculated, might be very materially reduced. The average consumption of coke by a locomotive engine, on a passage from Liverpool to Manchester, thirty-two miles is stated by Mr. Wood to be 800 pounds, and the water evaporated 225 gallons per hour and 450 gallons on the passage. Mr. Wood computes that one of those locomotives will perform the work of 240 horses travelling at the rate of ten miles per hour upon a turnpike road, the velocity of the locomotive being fifteen miles per hour. The fact is well established, that where the transportation is sufficient for supplying adequate loads for locomotive engines, and where the road is so constructed that they can be advantageously used, and where fuel is not exceedingly expensive, they afford much the most economical motive power.

HELIOGRAPHY.

The

It is remarkable, that producing images by means of light, and which has lately attracted so large a share of public attention, under the various names of Photography-Photogenic Drawing-the Daguerrotype, &c., should have been discovered by three different persons at the same time, and that

their methods should be totally distinct from each other-that of Mr. Fox Talbot, described so fully in our earlier numbers-that of M. Daguerre, explained in No. XXII-and that of M. J. N. Neipce, the account of whose process is as follows, given in Mr. Neipce's own words :

The discovery which I have made, and to which I give the name of Heliography, consists in reproducing spontaneously by the action of light, with the gradation of tints from black to white. the images received by the camera obscura.

Fundamental Principle of the Discovery.-Light, in its state of composition and decomposition, acts chemically upon bodies. It is absorbed, it com. bines with them, and communicates to them new properties. Thus it augments the natural consistency of some of these bodies: it solidifies them even, and renders them more or less insoluble according to the duration or intensity of its action.

Such, in a few words, is the principle of the discovery.

Primary Material. Preparation.-The substance or primary I employ-that which has succeeded best with me, and which concurs most immediately to produce the effect is asphaltum or bitumen of Judea, prepared in the following man

ner:

I fill a wine-glass about half with this pulverised bitumen. I pour upon it drop by drop the essential oil of lavender till the bitumen can absorb no more, and till it be completely saturated. I afterwards add as much more of the essential oil as causes the whole to stand about three lines above the mixture, which is then covered and submitted to a gentle heat until the whole essential oil be saturated with the coloring matter of the bitumen. If this varnish should not yet possess the requisite consistency, it is to be allowed to evaporate atmospherically in a dish, care being taken to protect it from moisture, by which it is injured, and finally decomposed. If in winter, or during rainy weather, the precaution is doubly necessary.

A small quantity of this varnish applied cold, with a light roll of very soft skin, to a highly polished tablet of plated silver, will impart to it a fine vermillion color, and will cover it with a very thin and equal coating; the plate is afterwards to be placed on heated iron, which is wrapped round with several folds of paper, whence by this means all the moisture has been previously expelled. When the varnish has ceased to simmer, the plate is withdrawn, and left to cool and dry in a gentle temperature, secured against contact with a damp atmosphere. I ought not to omit mentioning that it is principally in applying the varnish that this last precaution is indispensable. In this part of the operation, a light circle of metal, with a handle in the centre, should be held before the mouth in order to condense the moisture of the respiration.

The plate thus prepared may be immediately submitted in the focus of the camera to the impressions of the luminous fluid. But even, after having been thus exposed, a length of time sufficient for receiving the impressions of external objects, nothing is externally apparent to show that these impressions exist. The forms of the future picture remain still invisible. The next operation then is to disengage the shrouded imagery, and this is accomplished by a solvent.

Of the Solvent and Manner of its Preparation.— As the solvent must be adapted to the purposes for which it is designed, the task is difficult to fix with

MR. STURGEON was the first to form and apply the pot battery to the purposes of electro-magnetism; and that many years since, after having observed, that, in this science, the electric power might be diminished almost at pleasure, provided the magnetic power be increased in proportion to the diminution of the other element. Instead, therefore, of using the immense and expensive batteries of former times, he found that one, holding a pint, or at most a quart of liquid, was amply sufficient to occasion the usual magnetic deflections, rotations, &c. His battery is represented in Fig. 1. It consists of two copper cylinders, one placed within the other, and with a bottom connecting the two. The outer cylinder is about three inches diameter

and eight inches high, and has soldered on the outside of it a wire, bearing a wooden cup to hold mercury. The other part of the battery is a cylinder of zinc, of equal length to the coppers, and a diameter between each; it also has a wire and wooden cup soldered to it. To prevent the zinc, and copper touching each other when in use, three strips of wood may be fastened to it previously, or a wooden ring put on at the bottom of the zinc cylinder. To use this simple battery, fill it with a mixture of nitric acid and water, about one part of the former to twelve or fourteen of the latter-and by uniting the two cups a current of the fluid will circulate, which will be of considerable intensity; but from the violent chemical action which takes place, and

the rapid deposition of oxyde, it will be of short duration this, though a valuable instrument for the lecture table, yet is comparatively useless to show the chemical decompositions which depend upon long-continued galvanic action. The constant battery of Mr. Daniell remedies this defect, as it remains in action with scarcely diminished intensity for some days. It consists, (see Fig. 2,) of a copper vessel, three inches and a half in diameter, and varying in height, from sixteen to twenty inches, according to the power which it is wished to obtain ; withinside this, at the distance of three quarters of an inch or so, is a second cylinder, made of zinc, and without a bottom-each of these is furnished with a mercury cup, or what is more convenient, a small screw, which fixes the conducting wires in holes prepared for them so far there is nothing peculiar ; but Mr. Daniell, considering the cause of the decline of action being the various chemical decompositions going on, interposed between the copper and zinc, a membrane, formed of ox gullet, drawing it like a bag over the zinc cylinder; and also a rim, or shelf of copper, is placed withinside the copper vessel, perforated with holes. This is the whole construction of this simple instrument. To use it, the outer cell is filled with a saturated solution of sulphate of copper, (blue stone,) and portions of the solid salt are placed upon the circular plate, or shelf, for the purpose of keeping the solution always in a state of saturation. The internal tube is filled with a very weak solution of sulphuric acid and water, or it may be salt and water. A very great improvement upon this battery is to substitute for tox gullet, a porous porcelain tube, and instead of t. cylinder of zinc, a thick rod of that metal covered carefully with mercury, and merely supported at the top by a cross bar, as in Fig. 3. The mixture for this is, eight measures of water to one of oil of vitriol, which has been saturated with sulphate of copper for the outer compartment-placing crystals on the shelf as before, and the same mixture of acid and water, but without the copper for the inner space.

A number of such cells may be connected, the zinc side of one, and the copper side of the next, as shown in Fig. 4; thus making a complete and very powerful battery. Six of these, holding a pint each, may be used effectually with Mr. Bachhoffner's machine, described in the last number.

In this instrument the sulphate of zinc, formed by the solution of the zinc rod, is retained in the membranous bag, or the porous case, and prevented from diffusing itself to the copper surface; while the hydrogen, instead of being evolved as gas on the surface, of the latter metal decomposes the oxyde of copper of the salt there, and occasions a deposition of metallic copper on the copper-plate. Such a circle will not vary in its action for hours together, which makes it invaluable in the investigation of voltaic laws. It owes its superiority principally to these circumstances:-to the amalgamation of the zinc, which prevents the waste of that metal by solution when the circuit is not completed; to the non-occurrence of the precipitation of zinc upon the copper surface; and to the complete absorption of the hydrogen at the copper surface the addition of globules of gas to the metallic plates greatly diminishing, and introducing much irregularity into the action of a circle.

MANUFACTURE OF PENS. QUILLS appear to have been employed, at least, as early as the seventh century. England is supplied

with this article from Russia and Poland, where immense flocks of geese are fed for the sake of their quills. The quantity exported from St. Petersburgh, varies from six to twenty-seven millions. Twenty millions were last year imported into England from these countries. We may form some idea of the number of geese which must be required to afford the supply, when we consider, that each wing produces about five good quills, and that, by proper management, a goose may afford twenty quills during the year. Hence, it is obvious, that the geese of Great Britain and Ireland could afford but a very limited supply. The feathers of the geese of the latter countries are employed for making beds.

The preparation of quills, or touching, as it is called, is a curious and nice process. The Dutch possessed the complete monopoly of the quill manufacture until about 70 years ago, when the process was introduced into this country, and now our quills are infinitely superior to those of Holland.

The quills are first moistened, not by immersion, but by dipping their extremities into water, and allowing the remaining parts to absorb moisture by capillary attraction. They are then heated in the fire or in a charcoal chaffer, and are passed quickly under an instrument with a fine edge which flattens them, in such a manner as to render them apparently useless. They are then scraped, and again exposed to heat, when they are restored to their orignal form. This is a remarkable fact, and deserves to be attended to. It may be illustrated by taking a feather and crushing it with the hand, so as to destroy it to all appearances. If we now expose it to the action of steam or a similar temperature, it will speedily assume its pristine condition. Many of the quills, after this preparation, are cut into pens by means of the pen-cutter's knife, and are also trimmed. A pen cutter will cut in a day, two-thirds of a long thousand, which consists of 1,200, according to the stationers' computation. A house in Shoe-lane cuts generally about six millions of pens, and last year, notwithstanding the introduction of steel pens, it cut more then it had done in any previous years. According to the calculation of pen-makers, not more than one pen in ten is ever mended.

About thirty-one years ago, Mr. Bramah introduced portable pens into this country from New York, and took out a patent for their manufacture. The process for making portable pens is to form a vertical section of the barrel of the quill and polish the pieces. The pens are then cut with a beautiful instrument, each quill affording six pens. When they have been nipped coarsely, a polish is given with the pen-knife. Sixty thousand of these pens are manufactured weekly by two houses. An attempt was made to apply steel tips to portable quill pens, but the success which was anticipated did not follow.

Metallic pens appear to have been first introduced as rewards for merit, but steel pens for writing were first made by Mr. Wise, in 1803, and were fashioned like goose pens.

A patent was taken out in 1812 for pens with flat cheeks, and in this way all metallic pens were made for some time, as the rhodium pen of Dr. Wollaston, and the iridium pen of others. About fifteen years ago, Mr. Perry began to make pens, and about nine years ago they began to be manufactured at Birmingham. The steel is pressed