3655. Process for Covering Articles of Zinc with Copper or Brass by One Immersion

3655.    Process for Covering Articles of Zinc with Copper or Brass by One Immersion. To give zinc a coat of copper or brass for the purpose of a subsequent silvering or gilding, the following solutions are used: For copper alone, a solution of sulphate of copper, saturated at the common temperature, is mixed with a solution of cyanide of potassium, adding as much of the latter as is necessary to redissolve the precipitate thrown down at first. The prussic acid disengaged during this operation must be carried off by a draught or flue. When the mixture is clear, 1/10 or 1/5 of its volume of water of ammonia is added, and then diluted with water to a density of 8° Baumé. For brass, sulphate of copper and sulphate of zinc are used in equal proportion, and prepared as before. 2 parts sulphate of zinc and 1 of sulphate of copper give a bright brass coating. Previous to their dipping, the articles of zinc are rubbed off thoroughly with finely-powdered pumice-stone and rinsed in water, after which they are placed in the bath and remain there for 24 hours. After that time they are again rinsed in water and simply wiped off. The copper or brass covering has a very bright look, as if polished, and adheres perfectly. The thickness of the coat may be increased afterwards by the aid of a battery.

3656. Dullo's Method of Platinizing Glass

3656.    Dullo's Method of Platinizing Glass. This is recommended to prevent fusing of the thin end of a glass tube used for a blowpipe. In drawing out the end of the tube, leave the diameter slightly larger than is necessary; then roughen the narrow end with a file. Dip in a solution of bichloride of platinum, containing 5 per cent, of the metal; remove excess of the drop, and heat cautiously till the glass acquires a metallic appearance. Repeat this 4 or 5 times.

3657. Boettger's Method of Platinizing Glass

3657.    Boettger's Method of Platinizing Glass. Pour rosemary oil upon the dry chloride of platinum in a porcelain dish, and knead it well until all parts are moistened; then rub this up with 5 times its weight of lavender oil, and leave the liquid a short time to clarify. The objects to bo platinized are to be thinly coated with the above preparation and afterwards heated for a few minutes in a muffle or over a Bunsen burner.

3658. Platinizing Copper, Yellow Metal, and Brass

3658.      Platinizing Copper, Yellow Metal, and Brass. In order to obtain a platinizing fluid capable of platinizing copper, yellow metal, and brass, add to a moderately concentrated solution of chloride of platinum, finely powdered carbonate of soda, until effervescence ceases; next some glucose, and afterwards just so much common salt as will cause a whitish-colored precipitate. When it is desired to apply this mixture for platinizing, the objects to bo treated are placed in a vessel made of zinc and perforated with holes; the vessel is then placed, with its contents, for a few seconds in the mixture thus described, which, fast previous to using, should be heated to 140° Fahr. On being removed from the zinc vessel, the objects are to bo washed with water and dried in sawdust.