THE ELECTROTYPE.
The electro-galvanic current has in no case been more interestingly employed than in the process of electrotyping. It consists of a mode of obtaining the copy of coins, medals, engraved plates, and other objects, which may be easily illustrated.
HOW TO MAKE AN ELECTROTYPE APPARATUS.
Take an earthen jar and a porous tube; fill the tube with ten parts of water and one of sulphuric acid; put it into the jar, into which pour as much of a solution of sulphate of copper (blue vitriol) as will fill three parts of it; place in the tube a piece of zinc, to which a copper wire is soldered and bent round, so that one end be immersed in the sulphate of copper; and a deposit of the copper will be immediately formed upon the wire. If there be plenty of acid and water, so as to allow of the action enduring for a long time, this process will go on till it has deposited all the copper. This is the principle upon which electrotyping proceeds—a principle referable to electro-chemical decomposition.
TO OBTAIN THE COPY OF A COIN OR MEDAL.
Never place the original medal in the apparatus, or the deposited copper may adhere so tightly to it that the removal destroys the beauty of the medal. Having taken an impression in sealing-wax, cover the latter with black-lead, and attach a wire so that it is in contact with the black-lead. To the wire and cast thus arranged a piece of sheet or cast zinc, amalgamated with mercury, must be attached, and we are at once furnished with the materials for the battery, as the object to be copied supplies the place of the copper. The medal must always be placed horizontally. Now let the apparatus be charged with the solution, by pouring into the outer vessel a portion of the coppery solution, so that it will stand about an inch above the medal; then pour in the glass the dilute acid to the same height as the former; now introduce the zinc into the acid, and the object to be copied into the solution of copper, which will immediately be deposited on the medal, and when of a sufficient thickness may be taken off.
HEAT.
HEAT, OR CALORIC.
The chief agent in causing the repulsion or separation of the particles of bodies from each other is heat, or more correctly caloric, by which is understood the unknown cause of the effect called heat. Philosophers are not agreed upon the nature of this wonderful agent. It pervades all nature, is the cause of nearly all the changes that take place both in organic and inorganic matter, and has great influence in the meteorological phenomena which we observe in the atmosphere that surrounds our planet. It appears to be intimately connected with light, electricity, and magnetism—subjects which the genius of Faraday and others have investigated, and by their discoveries brought us nearer to the knowledge of the real nature of these most wonderful forces.
Caloric, then, exists in all bodies, and has a constant tendency to equalize itself, as far at least as its outward manifestation, called temperature, is concerned; for if a hot body be brought near colder ones, it will give up heat to them, until by its loss and their gain they all become of the same temperature; and this proceeds more or less rapidly, according as the original difference of temperature was greater or less. Some other circumstances also influence this equalization. The converse will take place on introducing a cold body among warmer ones, when heat will be abstracted from all the bodies within reach of its influence, until it has absorbed sufficient caloric to bring its own temperature to an equality with theirs. This is the true explanation of the apparent production of cold. When, for instance, an iceberg comes across a ship’s course, it appears to give out cold, whereas it has abstracted the heat from the air and sea in its neighborhood, and they in turn act upon the ship and everything in it, until one common temperature is produced in all the neighboring bodies.