Or soften wax or gutta percha with gentle heat and knead it over the model. Treat the impression thus formed in the same manner.
Plaster Casts for Electrotyping.— To use plaster as a mold for electro typing, dry it in an oven and boil it in a mixture of equal quantities of beeswax and rosin until it is satu rated. Cool, and cover evenly with a thin coating of black lead.
Experiment for Electrotyping.— Take an ordinary leaf, lay it on a hard surface, and knead over it a bit of soft gutta percha or wax to make a mold. A little experimenting will secure a perfect impression. Remove the leaf, heat the end of a wire, and thrust it through the mold; brush the face of the mold with black lead, var nish the back as above, and attach to the negative pole of a battery. Attach a piece of copper to the opposite pole, facing but not touching it, and cover both with a saturated solution of copper sulphate slightly acidulated with sulphuric acid. Thus a beau tiful model may be taken which will show every detail of the leaf.
Gold - plating Solution. — Mix 4 ounces of muriatic acid and 2 ounces of nitric acid; add 10 pennyweights of gold coin, 10 grains of pure cop per, and 8 grains of pure silver. Shake until all is dissolved except a silver sediment. Add 1 ounce of pul verized borax, 2 ounces of pulverized sulphate of iron, 50 grains of salt, and 2 quarts of hot distilled water. Mix or shake vigorously.
Let this mixture stand until all the metals have settled. When they have fully settled, pour off the liquor and wash the sediment perfectly clean, or until it ceases to be acid to the taste. This may be done by add ing hot water, shaking, allowing it to settle, and pouring off the water as often as necessary. The sediment consists of the chloride of gold of about 18 karats fineness. Add 21. ounces of cyanuret of potassium, 2 quarts of boiling distilled water, shake well, and let stand a day or two, when it will be ready for use.
Silver-plating Solution.—Shave 1 ounce of silver and cover with 2 ounces of pure nitric acid. Add dis
tilled water slowly, ounce or less at a time, as the silver dissolves. Use as little water as possible, and when all dissolved stir in 3 ounces of salt dissolved in 3 pints of water. Stir or shake and let the solution settle.
Wash the sediment until it is no lon ger acid to the taste, add 114 ounces of cyanuret of potassium and 16 ounces of distilled water, and let stand a day or two before using.
To Test Plated Metals.—To test silver plating on metals, dissolve ounce of bichromate of potassium in nitric acid. Rub the surface to be tested with pure alcohol or ether to kill grease or varnish. Apply a drop of this mixture, and rinse the article in cold water. Pure silver is indi cated by a blood-red stain; German silver by a brown stain which washes off ; Britannia metal by a black stain; mercury by specks of red, which wash off ; lead and bismuth by yellow stains; tin by a brown stain which turns yellow in water; and zinc by the active action of the liquid, the stain of which is soluble in water.
Gold Plating without Electricity. —Dissolve 1-1 ounces of gold amal gam in a mixture of 1 ounce of nitric acid and 2 ounces of muriatic acid. Add 6 ounces of alcohol and immerse the articles in this for about 15 minutes ; apply the solution with a. soft brush or cloth. The articles must first be cleaned by dipping them in dilute nitric acid or potash lye to remove grease and rust and to give an absolutely clean surface; oth erwise the amalgam will not adhere. Rinse, dry in sawdust or prepared chalk, wipe clean with tissue paper, and polish with chamois skin.
Or clean the articles as before, and apply gold amalgam with a fine, stiff brush. Set them in the oven and heat them until the mercury evapo rates, when their color will be a dull yellow. Mix equal parts of pow dered saltpeter and alum to a paste with water, and go over the gold coating with this mixture, using a brush. Apply heat until this solu tion is melted, then plunge the arti cles into cold water and afterwards polish.