To test gold for its genuineness, dissolve in chlorine water and the resultant solution will possess a slightly yellowing color.
Gold salt is prepared by dissolution of 8 parts of gold in aqua regia. Two parts of common salt are added and the solution evaporated to dryness. A second method consists in the dissolution of 1 part gold in a mixture of 1 part of nitric acid and 4 parts of hydro-chloric acid.
To give gold stains to brass the articles are to be immersed in a compound of:
5 1/2 drachms damp Carbonate of Copper,
3 drachms Caustic Soda,
2 ounces Water. It will be only a few minutes before the shades of color make their appearance, and by watching same the appearance of the exact shade can be observed. When this is obtained the article is to be rinsed in water and dried in fine, soft dust.
To purify gold, make a thorough mixture of:
1 part Vitriol (green), 1 part Sea Salt, 1 part Alum, 3 parts Brickdust.
Form this compound into a paste by the addition of a little wine vinegar, and place the gold in the center of it.
A good method for the testing of gold ware is presented by the touchstone, which is a kind of black. Silesian basalt. When you draw a piece of gold across its surface a gold streak is left, which is unaffected by nitric acid moistening and which differs from streaks left by brass and other base alloys, which rapidly dissolve.
To obtain a gray coating on zinc precipitate arsenic in a heated bath of 8 46-100 drachms sodium pyro-phosphate in 8 2-100 ounces arsenious and 1 3/4 drachms of 98 per cent. potassium cyanide to 1 quart of water. Use a current strong enough so that a strongly perceptible development of hydrogen ensues.
For anodes use either carbon plates or platinum sheets.
To give iron and steel a gray color first polish the article and then coat it with a mixture of 2 parts of sulphuric acid, a drop or two of acetic acid and 8 parts of butter antimony.
Copper, 18 parts; tin, 2 parts. Melt.
Bicarbonate of ammonia and sulphate of soda in strong solution for hand grenades to extinguish fire. This compound will keep indefinitely without losing its active properties if the bottle is kept well corked.
To harden cast-iron mix 2 ounces nitric acid and 2 pounds concentrated sulphuric acid with 2 1/2 gallons of water. The article is to be plunged into this mixture when at a cherry red heat.
A compound for hardening steel consists of 3 parts of yellow prussiate of potash pulverized, 1 part pulverized borax, 1 part pulverized saltpetre and 1/2 part sugar of lead, all intimately mixed. The steel to be hardened is heated to a red heat and is then taken from the fire and this powder scattered over it. The steel is then replaced in the fire and after being brought to the requisite heat is cooled in cold rain water.