(1320) Black Glass. (1327) Frankfort Black. (1331) Outside Brown Paint. (1334) Bronzing Brass.

The Manufacturer and Builder 8, 1892

(1320) Black Glass.
—The manufacturers of these objects keep it a profound secret. Black glass is now chiefly made in Venice, Italy, and in Germany; it is sold in pieces of different sizes to the manufacturers of jewelry, who cut and grind it. But it is futile to conceal such secrets from scientists. Dr. R. Kayser, a chemist, of Nuremberg, has analyzed several samples of this black glass, with the following result: silica, 56½ parts; alumina, 2; oxid of iron, 1¼; protoxid of manganese, 11¼; carbonate of lime, 8,9; sulphate of magnesia, 4; sulphate of soda, 3½; chlorid of sodium, 10½; chlorid of potash, ½; carbonate of soda, 11.9. A black glass rod, intended for making beads, contained, silica, 69¼, parts; alumina, 2; oxid of iron, 2½; protoxid of manganese, 11¼; lime, 7¼; magnesia, 1¾; soda, 5½. It appears from the above that the color may be due to the manganese. In order to test the practical application of this analysis, he made a mixture of the sand, soda, and pulverized common black said of manganese, and melted it in a glass furnace. He obtained a black glass which was even black in thin layers, but when drawn out into very thin threads, it was, as well as the splinters from it, very dark violet; while for the rest it was very similar to the black glass obtained from Venice.

(1327) Frankfort Black.
—This is a substance universally known and described in most all technical books, (see for instance Ures's dictionary.) It is made by calcimining vine branches, and other refuse of the wine culture in Germany. You ask if another black would do as well. This depends on the nature and use of the recipe, and this you do not give. Or Correspondents are especially requested to mention the page of our journal they refer to. We can not spare the time to hunt through six and a half volumes of our magizine to find the recipe where Frankfort black is mentioned.

(1331) Outside Brown Paint.
—Burnt sienna is reddish brown; if too red to suit your taste, you may mix in some burnt amber. The natural brownred iron oxid, sold for roofingpaint, may also do; it is cheaper.

(1334) Bronzing Brass.
—There are several ways: 1st. Dissolve 1 part of perchlorid of iron in 2 parts of water, and immerse the article in it until dark enough to suit. 2d. Boil the article in a solution of nitrate of copper. 3d. Dissolve 1 part of nitrate of iron and 1 part of hyposulphite of soda in 8 parts of water, and immerse the article. 4th. Wash the article with vinegar, then expose to the vapor of ammonia, and repeat this until dark enough.

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