Upon the central axis is a wheel, furnished with two steel dies upon it periphery, the length of each of which corresponds to the circumference of the coin to be milled; and on the trilateral spaces of the table, are firmly screwed blocks for the outside dies, furnished with the necessary adjusting screws, by means of which the proper degree of pressure is given. Upon the axis immediately above the central wheel, an oval cam, or eccentric, is placed, for the movement of the feeders; this cam is set in time to place the blanks between the dies, when the extremities of the latter are opposite to each other. The feeders are levers, moving on centres, placed on each of the three arms of the gallows which supports the upper ends of the axis; which levers are kept against the cam by spiral springs, contained within a cavity at the centre of motion. A circular blade, or pitcher, as it is technically called, takes the lowest blank from the pile contained in the feeding tubes, and pushes it forward, at the required moment, and a light curved spring prevents its being thrown in advance of the movement. Nearly all of the parts are exhibited in the annexed views.

This machine is triplicate, and all its feeders may be put in motion at the same time, or any one of them, as occasion may require. Each division is capable of milling 200 pieces, or more, per minute, equal to 12,000 per hour, with the attendance of a boy only; and during this rapid operation, separates any defective pieces that may pass into the tubes. This machine has been in operation since February of the present year, and has given unqualified satisfaction in every respect.

Observations on Microscopic Chemistry. By JNo. W. DRAPER, M. D. Professor of Chemistry and Natural Philosophy, Hampden Sidney College, Va.

1. One of the greatest obstacles to a more general study of scientific chemistry, is a prevailing opinion, that of all the various branches of knowledge, this demands more diversified resources, and entails upon those who prosecute it, an expenditure, usually beyond the means of private individuals.

2. It therefore is the duty of those who wish well to the science they cultivate, to point out the error of such an opinion. Within a few years there has been a complete revolution in chemical manipulation, or the mode of making experiments; a change, to which we are to ascribe the present rapid advance of the science. Operations on the large scale, are never performed, except by those who are public teachers, and here the neces sity of rendering effect visible at a distance, calls for a degree of magnitude in experimenting, that unfortunately leads the pupil to conclude, that such pursuits can only be followed by the possessors of large fortunes, and even that they would meet with "almost impossibilities," except they were residents of cities. Those large retorts, and bells, and complicated stop-cocks, and furnaces, the innumerable company of vials, and tests. and electrical machines, and galvanic batteries, could not be purchased in the country. This is a conclusion to which those who have a predilection for these studies are often led,—an unfortunate conclusion, for it restrains many a one who would otherwise be an active and efficient labourer in the field. Now, there are few chemists, even among those who reside in cities, and have the disposal of well appointed laboratories, who could not communicate a large stock of highly useful information to their less fortunate brethren. A man, who for a number of years, has been engaged in all kinds of operations of repetition and research, must of necessity be acquainted with a number of simple succedanea, both in the shape of operations and instruments, which at times have obtruded themselves upon his necessities. With this view, I propose to offer my mite, in the hope that it may stimulate others, who are far better able to extend this kind of information.

3. The specific properties of any kind of matter, are as well seen in a small particle as they are in a large mass. A piece of marble, not bigger than a pin's head, will furnish the same chemical results, as a piece of an ounce weight. Hence, if the operator possessed that delicacy, and tact which would enable him to work as well with the small quantity as with the large, his result would be equally striking, and equally true. Like all other sciences, in its Infancy chemistry had a degree of roughness, which offers a remarkable contrast with the neatness and finish of modern manipulation; instead of those enormous alembics, and colossal retorts, which dignify the works of the earlier writers, we now give instructions to perform the same distillations in fragments of quill tubes; the blow-pipe has replaced the hundreds of blast, and forge, and reverberating furnaces, over which the alchemist toiled, by the sweat of his brow, not, alas, gaining his bread; and the grain weight and cubic inch have become the units of the laboratory, instead of the pound and the gallon.

4. The manipulation of microscopic chemistry, consists in the art of working with small portions of matter. It requires a degree of manual dexterity which practice alone can give, but which if once gained, is of vast importance to the chemist. It reduces, to an indefinite extent, the charges

and expenses he incurs in a series of experiments; and, what is equally valuable, there is a great saving of time. A few minutes will often put him in possession of the same facts, that on the old plan he must have been hours or days in acquiring. Again, there are often circumstances under which he would be compelled to work on minute quantities, as perhaps in the detection of a poison in the stomach, or in the analysis of a precious substance, and here if his previous habits had not accustomed him to operations on the small scale, he would soon find himself quite incompetent to perform his task. In this point of view, perhaps future chemists will hereafter assign a much higher rank to Dr. Wollaston than to Sir H. Davy, the simple, refined and delicate experimenting of the former, affording a more useful guide than the dashing brilliancy of the latter.

5. It is not many years, since the mouth blow-pipe was transferred from the workshop of the jeweller, to the laboratory; it has already become one of our most powerful and useful implements, giving a command over a range of temperature nearly as high as the melting point of wrought iron. Still later the simple candle or lamp has been employed, without any means of urging the flame, and when properly managed, its applications are also very extensive; to the chemical student, it is an invaluable substitute for all kinds of extensive furnaces, and therefore deserves to be thoroughly understood. As there are many parts of the United States, where oil is with difficulty obtained, and lamps scarcely ever used, I propose first to make a few remarks on the power and method of using a tallow candle, as a source of heat.

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6. The range of temperature that can be commanded by a tallow candle, is by no means inconsiderable; it is well known that iron or steel filings sprinkled on the flame, are made at once white hot. And if a copper wire be presented to it, under certain circumstances, it will be fused in a few moments. This is a simple experiment, but one well deserving of repetition; so far however as I am aware, it has never yet been pointed out; it is striking, and perhaps in the hands of a skilful machinist, might have some useful applications. A thin copper wire, is to be bent into a spiral of six or eight turns, over a cylinder of wood, about the size of a black lead pencil; one end is left uncoiled as at a, to be used as a handle; the spiral is now to be put over the flame of a candle, whose wick has been fresh snuffed; it is to be arranged so as entirely to surround the flame, and held by the extremity a; the flame immediately, burns very dimly, and puts on a greenish hue, and the copper wire melts and falls down. complete and perfect is the abstraction of the heat from the flame, that I doubt not that if a narrow tube were placed under similar circumstances, and a stream of water forced with great velocity through it, it would be an advantageous mode, if not the most advantageous, of applying flame as a source of heating liquids.

So

7. A great variety of experiments are required, respecting the fusibility of minerals or other substances, and the characters they display in the fire; these for the most part, may be made by paying due attention to the size of the fragment operated on, viz. that it shall be sufficiently small, and that the support on which it is presented to the flame, be as fine as possible, and of a highly non-conducting material. It is the perfect fulfilment of these conditions, that enables a simple candle flame to burn iron filings. A little

cone made of white clay, and having a very fine point, is excellent in these respects, and is useful also in blow-pipe experiments.

8. There are certain minutiæ to be attended to, in working with a candle, that should here be noticed. They arise from the candle burning with a flickering flame, from the wick becoming too long and smutty, and requiring continual snuffing. This last inconvenience, may, however, be avoided by a simple expedient. Suppose it was required to dissolve a certain quan

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tity of any saline substance in boiling water, and that to effect the solution, would require the application of heat for several minutes. Having beaten the salt into small fragments, put it into a common vial, of such a size, that the amount of liquid shall not half fill it. Around the neck of the phial, double a strip of paper, the projecting ends of which are to be twisted into a handle, a. Now, if the candle be held in a vertical position, it will be found, that it would require continual snuffing at inconvenient moments; but, by inclining it at an angle to the horizon, as soon as the wick exceeds a certain length it projects beyond the edge of the flame, and is burnt off, by the continual access of atmospheric oxygen, and the candle never requires snuffing. In the operation before us, it will be found unsafe to apply the flame to the extremity of the phial, because nearly all phials are very thick in the bottom, and fracture would certainly ensue; but, by applying the heat an inch higher up, all kinds of solutions, distillations, &c., may be safely, cheaply, and expeditiously performed by this means. In the course of a few minutes, the liquid commences boiling, and the solution gradually proceeds; steam is copiously evolved from the mouth of the bottle, and the whole vessel attains a temperature which renders it inconvenient to touch; the advantages of the twisted paper handle are now apparent, since the vessel may be held in the hand, the elbow resting on the table, while steam is copiously rushing out of it, and all the phenomena of the solution distinctly seen.

9. In this, as well as all similar operations with candles, and also with lamps, there is an important observation to be attended to-it refers to the distance between the bottom of the vessel, and the top of the flame. It might be supposed that a maximum of temperature would be reached by plunging the vessel into the flame; such, however, is not the case; a copious deposit of carbonaceous matter at once covers the surface, and the high radiating power of this coating, exerts a powerful cooling effect. Nor is that all; every thing like cleanliness is entirely sacrificed; if the fingers happen to touch it, they become soiled, and it is impossible to see the action going on in the materials employed. All these inconveniences are avoided by placing the vessel half an inch, or if the flame flickers much, a whole inch above its apex; the cleanliness of the vessel is insured, there is an abundant supply of heat, and the operator can distinctly see any kind of reaction going on in the materials. It may be observed that these remarks do not apply to the spirit lamp.

10. When a candle thus arranged, is burning as it ought to do, its apex is not a cone, as a, but is as represented at b, ending in a kind of three pronged fork; the point of maximum available temperature, being about half an inch from the tips of the prongs. In an appropriate, but very simple arrangement of phials, such as will be shortly pointed out, evaporation and distillation to a certain extent, may thus

be carried on over a candle; the distillation of water, or the making of strong nitric acid, are thus readily accomplished. Except, however, when the vessels are exceedingly small, it will not be possible to distil sulphuric acid, or mercury, too high a temperature being demanded.

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11. Where oil is readily procured, the common oil lamp is a much more convenient implement than the candle, affording a more steady and constant flame, which can easily be protected from the agitation of currents of air, by a piece of sheet tin, two inches wide and three long, bent into a cylindrical form. This chimney ought to have its lower edge serrated, to admit a copious afflux of air, and at the same time to stand firm on

the lamp. Sheet tin, or copper, or brass, can be readily cut by a common pair of scissors, and that elasticity which sometimes hinders a piece from retaining the shape into which it may be bent, is overcome, by making it red-hot in the fire.

12. I have somewhere seen a description of a small portable furnace which is used by the Cingalese jewellers, and found it very eligible in experiments which demand the ignition of a larger mass than can be worked either with the simple candle, or blow-pipe. It consists of a shallow earthen tray; of the size and figure of a saucer, which is to be filled with sawdust, or finely chopped straw. On the surface of this non-conducting bed, a little charcoal fire is raised, one of the pieces of coal having been pre

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viously ignited. The fire is urged by blowing at it, through a piece of hollow reed, or tobacco pipe stem, or even through a straw; there is a certain distance, at which the pipe has to be held, to produce the most powerful effect, this is easily determined at the very first trial, by a peculiar roaring sound that the blast makes among the embers; this distance varies from 2 to 6 inches, depending on the degree of ignition, and the force with which the wind is urged. Gold, silver, and copper, may be melted in this furnace, when the fire is about as large as one's fist, and the igniting and crucible operations required in mineral analysis, may be conveniently performed

in it.

13. The bowl of an earthenware tobacco pipe, makes a suitable crucible for this furnace, the hole in the bottom of it being stopped by a pellet of clay. Persons, however, who reside where refractory clay can be procured, will find it convenient to accustom themselves to the manufacture of small vessels, such as crucibles, tubes, retorts, &c. And as knowledge of this kind gives a degree of independence to a chemist, affording him facilities for working without a long and vexatious delay in having to send to the cities for suitable implements, it is well for him to make himself master of it; the process for forming a crucible is as follows. A piece of wood, six or eight inches long, and of a suitable thickness, has one of its ends cut into a shape suitable for the inside of the vessel, it is finished off neatly with a file, and no projecting part, or asperities, left; it should be considerably longer than the height of the intended crucible. The clay is to be prepared, by picking out from it any little pebbles, grit, or any other impurity, and bring it by kneading with a due quantity of water, to the condition of a stiff homogeneous paste. A small cylinder of it, is then to be rolled out on a board, until it is about one-sixth or one-eighth of an inch thick, observing not to roll it out entirely on one side, but after having