The ink made by the prescription given above, is much more rich and powerful than many of the inks commonly sold. To bring it to their standard, a half more water may safely be added, or even 20 gallons of tolerable ink may be made from that weight of materials.

Sumach and logwood admit of only about onehalf of the copperas that galls will take to bring out the maximum amount of black dye.

Chaptal gives a prescription in his Chimie appliquee aux arts, which like many other things in that work, are published with very little knowledge and discrimination. He uses logwood and sulphate of copper in addition to the galls and sulphate of iron; a pernicious combination productive of a spurious fugitive black, and a liquor corrosive of pens. It is in fact, a modification of

the dye of the hatters.

Lewis, who made exact experiments on inks, assigned the proportion of 3 parts of galls to 1 of sulphate of iron, which, with average galls, will answer very well; but good galls will admit of more copperas.

Gold Ink is made by grinding upon a porphyry slab, with a muller, gold leaves along with white honey, till they be reduced to the finest possible division. The paste is then collected upon the edge of a knife or spatula, put into a large glass, and diffused through water. The gold by gravity soon falls to the bottom, while the honey dissolves in the water, which must be decanted off. sediment is to be repeatedly washed till entirely freed from the honey. The powder, when dried, is very brilliant, and when to be used as an ink, may be mixed up with a little gum water. After the writing becomes dry, it should be burnished with a wolf's tooth.

The

Silver Ink is prepared in the same manner. Indelible Ink.-A very good ink, capable of resisting chlorine, oxalic acid, and ablution with a hair pencil or sponge, may be made by mixing some of the ink made by the preceding prescription, with a little genuine China ink. It writes well. Many other formulæ have been given for indelible inks, but they are all inferior in simplicity and usefulness to the one now prescribed. Solution of nitrate of silver thickened with gum, and written with upon linen or cotton cloth, previously imbued with a solution of soda, and dried, is the ordinary permanent ink of the shops. Before the cloths are washed, the writing should be exposed to the sun-beams, or to bright daylight, which blackens and fixes the oxide of silver. It is easily discharged by chlorine and ammonia.

A

Red Ink. This ink may be made by infusing, for three or four days, in weak vinegar, Brazil wood chipped into small pieces; the infusion may be then boiled upon the wood for an hour, strained, and thickened slightly with gum arabic and water. little alum improves the color. A decoction of cochineal with a little water of ammonia, forms a more beautiful red ink, but it is fugitive. An extemporaneous red ink of the same kind may be made by dissolving carmine in weak water of ammonia, and adding a little mucilage.

Green Ink.-According to Klaproth, a fine ink of this color may be prepared by boiling a mixture of 2 parts of verdigris in 8 parts of water, with 1 of cream of tartar, till the total bulk be reduced one-half. The solution must be then passed through a cloth, cooled, and bottled for use.

Yellow Ink is made by dissolving 3 parts of alum

in 100 of water, adding 25 parts of Persian or Avignon berries bruised, boiling the mixture for an hour, straining the liquor, and dissolving it in 4 parts of gum arabic. A solution of gamboge in water forms a convenient yellow ink.

By examining the different dye-stuffs, and considering the process used in dyeing with them, a variety of colored inks may be made.

China Ink.-Proust says, that lamp-black purified by potash lye, when mixed with a solution of glue, and dried, formed an ink which was preferred by artists to that of China. M. Merimée says, that the Chinese do not use glue in the fabrication of their ink, but that they add vegetable juices, which render it more brilliant and more indelible upon paper. When the best lampblack is levigated with the purest gelatine or solution of glue, it forms, no doubt, an ink of a good color, but wants the shining fracture, and is not so permanent on paper as good China ink; and it stiffens in cold weather into a tremulous jelly. Glue may be deprived of the gelatinizing property by boiling it for a long time, or subjecting it to a high heat in a Papin's digester: but as ammonia is apt to be generated in this way, M. Merimée recommends starch gum made by sulphuric acid, (British gum,) to be used in preference to glue. He gives, however, the following directions for preparing this ink with glue. Into a solution of glue he pours a concentrated solution of gall-nuts, which occasions an elastic resinous-looking precipitate. He washes this matter with hot water, and dissolves it in a spare solution of clarified glue. He filters anew, and concentrates it to the proper degree for being incorporated with the purified lamp-black. The astringent principle in vegetables does not precipitate gelatine when its acid is saturated; as is done by boiling the nut-galls with lime water or magnesia. The first mode of making the ink is to be preferred. The lamp-black is said to be made in China by collecting the smoke of the oil of sesame. A little camphor (about 2 per cent.) has been detected in the ink of China, and is supposed to improve it. Infusion of galls renders the ink permanent on paper.

ELASTIC MOULDS.

BEING much engaged in taking casts from anatomical preparations, Dr. Douglas Fox, Surgeon, of Derby, found great difficulty, principally with hard bodies, which, when undercut, or having considerable overlaps, did not admit of the removal of moulds of the ordinary kind, except with injury. These difficulties suggested to him the use of elastic moulds, which, giving way as they were withdrawn from complicated parts, would return to their proper shape; and he ultimately succeeded in making such moulds of glue, which not only relieved him from all his difficulties, but were attended with great advantages, in consequence of the small number of pieces into which it was necessary to divide the mould.

:

The body to be moulded, previously oiled, must be secured one inch above the surface of a board, and then surrounded by a wall of clay, about an inch distant from its sides. The clay must also extend rather higher than the contained body into this, warm melted glue, as thick as possible so that it will run, is to be poured, so as to completely cover the body to be moulded: the glue is to remain till cold, when it will have set into an elastic mass, just such as is required.

Having removed the clay, the glue is to be cut into as many pieces as may be necessary for its removal, either by a sharp-pointed knife, or by having placed threads in the requisite situation of the body to be moulded, which may be drawn away when the glue is set, so as to cut it out in any direction.

The portions of the glue mould having been removed from the original, are to placed together and bound round by tape.

In some instances it is well to run small wooden pegs through the portions of the glue, so as to keep them exactly in their proper positions. If the mould be of considerable size, it is better to let it be bound with moderate tightness upon a board, to prevent it bending whilst in use; having done as above described, the plaster of Paris, as in common casting, is to be poured into the mould, and left to

set.

In many instances wax may also be cast in glue, if it is not poured in whilst too hot; as the wax cools so rapidly when applied to the cold glue, that the sharpness of the impression is not injured.

Glue has been described as succeeding well where an elastic mould is alone applicable; but many modifications are admissible. When the moulds are not used soon after being made, treacle should be previously mixed with the glue, to prevent its becoming hard.

The description thus given is with reference to moulding those bodies which cannot be so well 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.

ELECTRICITY.

(Resumed from page 131.)

TWO THEORIES OF ELECTRICITY.

IN a very early stage of electrical inquiry, it was observed that there was a remarkable difference of effect manifested by different substances when excited. Ex.-Charge two insulated pith balls by holding near them an excited glass tube, the balls will separate from each other; the same is the effect when both are charged by holding to them an excited stick of sealing wax, yet when one is electrified by the glass and the other by the wax, they are mutually attracted.

This circumstance gave rise to the opinion that two different species of the electric fluid existed, a theory first promulgated to the world by M. Du Fay, who called the two fluids by names accordant to the substances which produce them; that produced by the friction of glass he called vitreous, and that caused by exciting sealing wax, the resinous.

This opinion of Du Fay was eagerly adopted by the electricians of Europe, who by it were enabled to account for all the appearances their experiments elicited, but when it became known that the same substance sometimes showed the vitreous and sometimes the resinous, the names given to the two fluids became inapplicable, and when the Leyden phial was discovered, they were at a loss to explain its action by this hypothesis. Dr. Franklin, with his usual sagacity, founded the other theory; not indeed a perfect system, but one which rapidly ran over Europe and America, for it was the only one which could explain the action of the Leyden jar, which at that time engaged the whole attention of

the learned. He imagined that there was but one fluid, and that all bodies whatever contained a certain quantity of that fluid; which quantity we may increase or decrease at our pleasure. When increased he styles it plus, or positive electricity, and when a diminution takes place, he calls it minus, or negatively electrified, which terms positive and negative are now universally applied when speaking of electrified bodies. Not being able to explain the action of the Leyden jar was not the only reason for doubting the truth of M. Du Fay's theory, for it was soon discovered that the same body showed sometimes the resinous, sometimes the vitreous effect; how could this be accounted for? On the other hand, by Franklin's hypothesis nothing is more easy. The different effect is produced by the state of the rubber, as it is found that when two substances are rubbed together, so as to exhibit electrical appearances, that one of them is always positive and the other negative. The following list of substances is so arranged, that when either is rubbed with any of the bodies placed above it, it becomes negative, and rubbed with any standing below it shows signs of positive electricity

Back of a cat.
Smooth glass.
Woollen cloth.
Feathers.
Wood.
Paper.
Silk.

Gum lac.

Roughened glass.

Thus if a tube of smooth glass be rubbed with a woollen cloth, or a silk handkerchief, it becomes electrified positively, as these bodies stand under it in the table, but if glass be rubbed with cat's fur it becomes negative; in the former case, it absorbs the fluids from the materials rubbed against it, and therefore becomes overcharged; in the latter case it shows a negative property, in consequence of parting with a portion of its natural share, to the cat's skin-thus, as Franklin would have said, it has a superfluity in one case, in the other a deficiency.

Nothing can possibly be more easy to understand than this, and in every case in which the theory can be applied, equal facility can be offered, or at any rate there is no fact which cannot be explained by this hypothesis, except indeed such as are equally unintelligible by the other also.

But in giving an opinion on any disputed point of philosophy, it is right to state the arguments for and against any particular view, and to institute a fair comparison, by explaining the foregoing experiment by means of Du Fay's theory. Those of his school believe that there are two electric fluids, antagonistic to each other, and that when one of these is by any means disturbed, the other is equally so-thus it supposes two causes for a single effect, certainly an anomaly in physics. In the rubbing of the glass tube with a woollen cloth, and thereby producing an electrical action, two fluids then are disturbed, which two, nevertheless, exist in each body; and when the glass and cloth are separated, still the fluids do not coalesce, though both are present in every portion of the glass, and also of the woollen. Why this is nobody can tell, nor is an attempt at explanation given at all. It has been said, that there are many circumstances to invalidate the Franklinian hypothesis-the strongest of which is, that when a shock is passed through a card there are often two holes made in it, there

fore, there must necessarily be two fluids passingeach of which has its appointed channel. Nothing can be more easy than to explain the reason of these various perforations. Is it not, also, the fact that if the water of a river meets with an obstacle, it divides into two streams, though it still passes on in its general course? And thus it is with the electric fluid. The card is the obstacle, being a bad conductor, which occasions the fluid to break into two streams there are seldom more than two, because the fluid requires no more channels; sometimes, and, indeed, most frequently, but one, and then one hole only is apparent. The same experiment affords a second objection to the one-fluid theory. If a shock be passed through a damp card, a burr, or rough edge, will be found on each side of it, which some persons believe to be an incontestible proof of two fluids, one passing in each direction. The experiment really proves no such thing, and may be imitated many ways-by the passage of one body only through another: thus, when a leaden ball is fired from a musket against a sheet of 'copper, with sufficient force to pass through it, a double burr will be very plainly distinguishable; so also enlarge a hole that has been made in an iron hoop, with a semi-circular tapering bit, such as is used for metals, and a very strong burr will be found on each side of the hole. In these instances it is certain that but one body is in motion-why then should a similar appearance in the card prove that there are two fluids in motion? There is truly no appearance of a double stream in any electrical experiment whatever. Pass a shock over the surface of a card covered with vermillion, a single black mark will appear. In lightning there is but a flash in one direction, no counter flash meets it in its course. When a shock is sent along an exhausted glass tube, so as to imitate a falling star, or when a falling star is seen in the heavens, no other stream of fire is apparent; and also the circumstance of the luminous star visible on the negative side of the apparatus, and the brush on the positive side, is wholly inexplicable by the system of Du Fay, though nothing is easier by the more simple and more philosophical hypothesis of Franklin.

(Continued on page 177.)

MANUFACTURE OF WAFERS.

THERE are two manners of manufacturing wafers: 1, with wheat flour and water, for the ordinary kind; and 2, with gelatine. 1. A certain quantity of fine flour is to be diffused through pure water, and so mixed as to leave no clotty particles. This thin pap is then colored with one or other of the matters to be particularly described under the second head; and which are, vermillion, sulphate of indigo, and gamboge. The pap is not allowed to ferment, but must be employed immediately after it is mixed. For this purpose a tool is employed, consisting of two plates of iron, which come together like pincers or a pair of tongs, leaving a certain small definite space betwixt them. These plates are first slightly heated, greased with butter, filled with the pap, closed, and then exposed for a short time to the heat of a charcoal fire. The iron plates being allowed to cool, on opening them, the thin cake appears dry, solid, brittle, and about as thick as a playing-card. By means of annular punches of different sizes, with sharp edges, the cake is cut into wafers,

2. The transparent wafers are made as follows:Dissolve fine glue, or isinglass, in such a quantity of water, that the solution, when cold, may be consistent. Let it be poured hot upon a plate of mirror glass, (previously warmed with steam, and slightly greased,) which is fitted in a metallic frame with edges just as high as the wafers should be thick. A second plate of glass, heated and greased, is laid on the surface, so as to touch every point of the gelatine, resting on the edges of the frame. By this pressure, the thin cake of gelatine is made perfectly uniform. When the two plates of glass get cold, the gelatine becomes solid, and may easily be removed. It is then cut with proper punches into discs of different sizes.

The coloring-matters ought not to be of an insalubrious kind.

For red wafers, carmine is well adapted, when they are not to be transparent; but this color is dear, and can be used only for the finer kinds. Instead of it, a decoction of Brazil wood, brightened with a little alum, may be employed.

For yellow, an infusion of saffron or turmeric has been prescribed; but a decoction of weld, fustic, or Persian berries, might be used.

Sulphate of indigo partially saturated with potash, is used for the blue wafers; and this mixed with yellow for the greens. Some recommend the sulphate to be nearly neutralized with chalk, and to treat the liquor with alcohol, in order to obtain the best blue dye for wafers.

Common wafers are, however, colored with the substances mentioned at the beginning of the article; and for the cheaper kinds, red lead is used instead of vermillion, and turmeric instead of gamboge.

LAYING OUT THE TEETH OF WHEELS. As there are very uncommon and odd numbers of teeth in some of the wheels of astronomical clocks, and which, consequently, could not be cut by any common engine used by clock-makers for cutting the numbers of teeth in their clock-wheels, it is often necessary to divide the circumference of a circle into any given odd or even number of equal parts, so as that number may be laid down upon the dividing plate of a cutting engine.

There is no odd number, but from which, if a certain number be subtracted, there will remain an even number, easy to be subdivided. Thus, supposing the given number of equal divisions of a circle on the dividing plate to be 69; subtract 9, and there will remain 60.

Every circle is supposed to contain 360 degrees : therefore say, As the given number of parts in the circle, which is 69, is to 360 degrees, so is 9 parts to the corresponding arc of the circle that will contain them; which arc, by the Rule of Three, will be found to be 46.95. Therefore by the line of chords on a common scale, or rather on a sector, set off 46.95 (or 46·9) degrees with your compasses, in the periphery of the circle, and divide that arc or portion of the circle into 9 equal parts, and the rest of the circle into 60; and the whole will be divided into 69 equal parts, as was required.

Again, suppose it were required to divide the circumference of a circle into 83 equal parts; subtract 3, and 80 will remain. Then, as 83 parts are to 360 degrees, so (by the Rule of Proportion,) are parts to 13 degrees and one hundredth part of degree; which small fraction may be neglected

THE MOUTH BLOW-PIPE.

In the chemical analysis of mineral substances, it is generally necessary first to submit them to the action of the blow-pipe; by which operation their general nature is most frequently determined, and should not the heat to which they are now subjected reveal all their constituent principles, it will show at least some of them, and render the remainder more easily to be detected by the tests to be applied afterwards. The construction and manner of using this valuable instrument in its more simple forms will afford a good subject for the present paper.

Originally the mouth blow-pipe was only a simple conical tube, more or less curved towards its point, and terminated by a very small circular opening. Fig. 2.

is desirable to elevate the temperature. Workers in metal still derive immense advantages from this little instrument. They employ it in the soldering of very small articles, as well as for heating the extremities of delicate tools in order to temper them. Since the blow-pipe has fallen into the hands of mineralogical chemists its form has been subjected to a series of important modifications: one of them is hoving a bulb upon the stem, whereby the moisture of the breath is retained, and, therefore, the jet of air at the orifice is stronger and steadier. This form of blow-pipe is represented in

Fig. 3.

By means of this a current of air is carried against the flame of a candle, and the inflamed matter of the wick is directed upon small objects, of which it [SECOND EDITION.]

It was first used by the celebrated chemist, Bergman. Many other chemists modified the above. Black's blow-pipe was a tube narrowest at the mouth, and having a small jet, sideways on the principal tube. This required a less constrained position of the hands than the former. Wollaston used a small tube, similar to Fig. 2, but straight,