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Barytic Photographic Solution

Dissolve 35 grains chloride of barium in 2 ounces distilled water. bone ashes or burnt bones. At the British mint the cupels are made of the calcined cores of ox-horns. The powder is slightly moistened with water, and a circular steel mould is filled therewith, and after being pressed down tight, is finished off with a rammer, having a convex face of polished steel, which is struck forcibly with a mallet, until the mass becomes sufficiently hard and adherent. The cupel is then carefully removed, and exposed in the air to dry, which usually takes from 14 to 21 days. The muffle, with the cupels properly arranged, being placed in the furnace, the latter is filled up with charcoal, and lighted at the top by placing a few pieces, heated to whiteness, on last. When the cupels have 3182. Chromate Photographic Solutions. Simple chromate solution is a sat- been exposed for half an hour, and have beurated solution of bichromate of potash; a come white by heat, the lead is put into them little sulphate of indigo being sometimes add- by means of a pair of tongs, and as soon as ed to vary the color. this becomes thoroughly red and circulating,

The compound chromate solution consists as it is called, the metal to be assayed, wrap. of 10 grains bichromate of potash, and 20 ped in a small piece of paper, is added, and grains sulphate of copper, dissolved in 1 ounce the fire kept up strongly until the metal enters distilled water. the lead, and circulates well, when the heat 3183. Hydriodate of Iron and Bary- may be slightly diminished, and so regulated tes Photographic Solution. Hydriodate that the assay shall appear convex and ardent, of barytes, 40 grains; water, 1 ounce; pure while the cupel is less red-that the undulathe cupel is less red-that the undulasulphate of iron, 5 grains, mix, filter, add a tions shall circulate in all directions, and that drop or two diluted sulphuric acid, and when the middle of the metal shall appear smooth, settled decant the clear liquor for use. surrounded with a small circle of litharge, 3184. Hardwich's Gold Toning Bath which is being continually absorbed by the for Positive Printing. Pure chloride of cupel. This treatment must be continued gold, 1 grain; hyposulphite of soda, 1 to 3 until the metal becomes bright and shining, grains; hydrochloric acid, 4 minims; water, 4 or is said to "lighten;" after which certain ounces. prismatic colors, or rainbow hues, suddenly 3185. Mayall's Method of Cleaning flash across the globules, and undulate and Photographic Glasses. Snake up together cross each other, and the latter metal soon 30 parts alcohol, 10 parts strong liquid am- after appears very brilliant and clear, and at monia, 40 parts water, and 30 parts fine Tri-length becomes fixed and solid. This is called GOLD.

The most marked properties of the "brightening," and shows that the separa-produced by using a lead solution thickened tion is ended. In conducting this process, all with gum tragacanth on brass which has the materials used must be accurately weigh- been heated to 210° Fahr., and afterwards ed, especially the weight of the alloy before treated by the usual solution of sulphide of cupellation, and the resulting button of pure lead. The solution may be used several metal. The difference gives the quantity of times, and is not liable to spontaneous change. alloy. The preceding general description of the process of cupellation will render the following articles intelligible, without again entering into the minutiæ of the operation. An assay is thought to be good when the bead is metallic gold are its ductility, malleabilof a round form, with its upper surface bril- ity, and insolubility in all menstrua, except liant, its lower one granular and dead-white, aqua regia and aqueous chlorine, and nd its its slight and when it separates readily from the cupel. affinity for oxygen. Native gold has a spe- When the surface of the bead is dull and flat, cific gravity of 13.3 to 17.7; pure gold, about it shows that too much heat has been em- 19.3; its greatest density is 19.5. Its fuployed; and if the metal be silver, some may sing point is 2016° Fahr. It is characterized have been lost in the process, by fuming or by its yellow color, its insolubility in nitric absorption. When the bead is spongy, and acid, and ready solution in nitromuriatic acid of various colors, and scales of litharge still (aqua regia), forming a yellow liquid that remain on the cupel, and the metal adheres stains the skin purple. strongly to the latter, too little heat has been

3190. Assay of Gold by the Use of used, and the button still retains some lead. Touch-Stones. When it is desired to as- To remedy this, the heat should be raised, and certain the fineness of small quantities of a little powdered charcoal, or a few small gold, as in jewelry, &c., touch-needles and pieces of paper, thrown into the cupel, until stones are employed. The former are made the metal again begins to circulate freely. It in sets, containing gold of different fineness is necessary that the lead employed in the and differently alloyed with copper and silprocess of cupellation should be perfectly ver. Pieces of black pottery form excellent pure. It ought, therefore, to be procured by touch-stones. The mode of using them is to reducing refined litharge. (Cooley.) mark the stone with the sample under exam- 3188. Puscher's Solution for Coloring ination, and to compare its appearance, hard Metals. This is a new method of giving ness, &c., with that produced by one or more metals a durable colored coating, and can be of the needles. When the two are similar, executed quickly and cheaply. To prepare the quality is considered to be the same. the solution dissolve 14 ounces hyposulphite They are then further examined by moistenof soda in 1 pound water, and add 14 ounces ing the stroke with aquafortis when red hot, acetate of lead dissolved in 1/2 pound of water.

When this clear solution is heated to 190° to 210 Fahr., it decomposes slowly, and precipitates sulphide of lead in brown flocks. If metal is now immersed in it a part of the sulphide of lead is deposited thereon, and according to the length of time and consequent thickness of the deposited sulphide of lead, the various and beautiful lustre colors are produced. In 5 minutes there may be imparted to brass articles a color varying from a beautiful gold to a copper red; then carmine red; then dark, then light aniline blue, to a blue white, like sulphide of lead; and at last a reddish white, according to the length of time they remain in the solution used. The colors possess the most beautiful lustre, and if the articles to be colored have been previously thoroughly cleaned by means of acids and alkalies, they adhere so firmly that they may be operated upon by the polishing steel. To produce an even coloring, the articles to be colored must be evenly heated. when the appearances resulting from oxida tion, etc., differ according to the nature and quantity of the alloy.