with the least tractable substance. For use, wrap a ball of the ground in a piece of fine and close silk (taffeta), and tie this together with a string.

6. Means of heating the Plate.—Any source of heat emitting no smoke will do, such as a kitchen stove, a spirit lamp, or a small quantity of alcohol poured on a plate and ignited (when the time arrives).

7. A Hand Vice with a wooden handle, for holding the plate while heating it; price about seventy-five cents at the hardware-stores. But a small monkey-wrench will do as well, and for this experiment you can even get along with a pair of pincers.

8. A Dabber for laying the ground on the plate. Cut a piece of stout card-board, two or three inches in diameter; on this lay a bunch of horse-hair, freed from all dust, and over this again some cotton wool. Cover the whole with one or two pieces of clean taffeta (a clean piece of an old silk dress will do), draw them together tightly over the card-board, and tie with a string. When finished the thing will look something like a lady's toilet-ball. The horse-hair is not absolutely necessary, and may be omitted.

9. Means of Smoking the Ground.—The ground when laid on the plate with the dabber, is quite transparent and allows the glitter of the metal to shine through. To obtain a better working surface the ground is blackened by smoking it. For this purpose the thin wax-tapers known to Germans as “Wachsstock,” generally sold at German toy-stores, are the best. They come in balls. Cut the tapers into lengths, and twist six of them together. In default of these tapers, roll a piece of cotton cloth into a roll about as thick and as long as your middle finger, and soak one end of it in common lamp or sperm oil.

10. Stopping-out Varnish, used for protecting the back and the edges of the plate, and for “stopping out,” of which more hereafter. If you cannot buy it you can make it by dissolving an ounce of asphaltum, the same as that used for the ground, in about an ounce and a half of spirits of turpentine. Add the asphaltum to the turpentine little by little; shake the bottle containing the mixture frequently; keep it in the sun or a moderately warm place. The operation will require several days. The solution when finished should be of the consistency of thick honey.

11. Camel's-Hair Brushes, two or three of different sizes, for laying on the stopping-out varnish, and for other purposes.

12. Etching Points or Needles, for scratching the lines into the ground. Rat-tail files of good quality, costing about twenty cents each at the hardware-stores, are excellent for the purpose. Two are all you need for your experiment, and even one will be sufficient. Still cheaper points can be made of sewing, knitting, or any other kind of needles, mounted in sticks of wood like the lead of a lead-pencil. Use glue or sealing-wax to fasten them in the wood.

13. An Oil-Stone for grinding the points.

14. An Etching-Tray to hold the acid during the operation of biting. Trays are made of glass, porcelain, or india-rubber, and can generally be had at the photographer's supply-stores. A small india-rubber tray, large enough for your experiment, measuring four by five inches, costs fifty-five cents. But you can make an excellent tray yourself of paper. Make a box, of the required size and about one and a half inches high, of pasteboard, covered over by several layers of strong paper, well glued on. If you can manage to make a lip or spout in one of the corners, so much the better. After the glue has well dried pour stopping-out varnish into the box, and float it all over the bottom and the sides; pour the residue of the varnish back into your bottle, and allow the varnish in the box to dry; then paint the outside of the box with the same varnish. Repeat this process three or four times. Such a tray, with an occasional fresh coating of varnish, will last forever. For your experiment, however, any small porcelain (not earthenware) or glass dish will do, if it is only large enough to hold your plate, and allow the acid to stand over it to the height of about half an inch.

15. A Plate-Lifter, to lift your plate into and out of the bath without soiling your fingers. It consists of two pieces of string, each say twelve to fifteen inches long, tied to two cross-pieces of wood, each about six inches long, thus . It is well to keep the fingers out of the acid, as it causes yellow spots on the skin, which remain till they wear off.

16. Nitric Acid for biting in the lines. Any nitric acid sold by druggists will do, but the best is the so-called chemically pure nitric acid made by Messrs. Powers & Weightman, of Philadelphia. It comes put up in glass-stoppered bottles, the smallest of which hold one pound, and sell for about sixty cents.

17. Water for mixing with the acid and for washing the plate.

18. Blotting-Paper, soft and thick, several sheets, to dry the plate, as will be seen hereafter.

19. Spirits of Hartshorn or Volatile Alkali.—This is not needed for etching, but it is well to have it at hand, in case you should spatter your clothes with acid. Spots produced by the acid can generally be removed by rubbing with the alkali, which neutralizes the acid.

3. Grounding the Plate.—Having procured all these requisites, the first thing to do will be to clean the plate so as to remove any oil or other impurities that may have been left on it by the plate-maker. Wash and rub it well on both sides with a soft cotton rag and benzine, and then rub with whiting, as you would do if you were to clean a door-plate. Take care to remove all the whiting with a clean rag. Now take hold of your plate by one of its corners with the hand-vice, wrench, or pincers, between the jaws of which you have put a bit of card-board or stout paper, so as not to mark the plate. Hold it over the stove, spirit lamp, or ignited alcohol, and see to it that it is heated evenly throughout. Hold the plate in your left hand while heating it, and with the other press against it the ball of ground wrapped up in silk. As soon as you see the ground melting through the silk, distribute it over the plate by rubbing the ball all over its surface (the polished surface, as a matter of course), taking care the while that the plate remains just hot enough to melt the ground. If it is too hot, the ground will commence to boil and will finally burn. The bubbles caused by boiling are liable to leave air-holes in the ground through which the acid may bite little holes in the plate; burning ruins the ground altogether, so that it loses its power of withstanding the acid. After you have distributed the ground tolerably evenly, and in a thin layer, lay the plate down on the table (keeping hold of it, however, by the corner), and finish the distribution of the ground by dabbing with the dabber. Strike the plate quickly and with some force at first, and treat it more gently as the ground begins to cool. If it should have cooled too much, before the distribution is accomplished to your satisfaction, in which case the dabber will draw threads, heat the plate gently. The dabber not only equalizes the distribution of the varnish, but also removes what is superfluous. An extremely thin layer of ground is sufficient.

4. Smoking the Plate.—While the plate is yet hot, and the ground soft, it must