The tripoli which is used for polishing of soft metals, being used first with oil and then dried, is a yellow powder which consists almost entirely of the abundant shells of microscopic organisms.
Tutania is composed of:
To ungild copper, which is unable to stand glowing, the gold can be dissolved by being dipped in a warm mixture of 2 64-100 ounces of concentrated hydrochloric acid, 1 pound fuming sulphuric acid, and 1 3-10 ounces of nitric acid of 40 degrees Be. Before these articles are treated in this bath they should be perfectly dry, and the bath itself should not be diluted with water, in which case the acid would act upon the base metals.
To remove the gilding from articles of iron and steel they should be given treatment as the anode in a solution of from 2 to 2 3/4 oz. of 98 per cent. potassium-cyanide in 1 qt. of water and held over a copper-plate, greased with tallow or oil as the cathode.
To remove the gilding from silverware heat same until it glows, and then plunge in diluted sulphuric acid, which will cause the layer of gold to peel off. This process is to be repeated until the removal of all the gold. Prior to the glowing and immersion, the articles may be given a coat of a paste composed of flour of sulphur, sal-ammonium, potassium, nitrate of borax, this paste being allowed to dry. The gold in the gilding will be found on the bottom of the vessel holding the boiled sulphuric acid in the form of scales and laminae. Boil these scales and laminae with pure sulphuric acid, wash them, followed by their dissolution in aqua regia, and make them into chloride of gold or fulminating gold.
For untinning tinplate scraps, use a large pot containing soda, lye, and oxide of lead. About 3 per cent. tin is obtained by the process.
A bright asphalt varnish for sheet metals is made by boiling cold tar until it shows a disposition to become hard, when it gets cool. This can be found out by rubbing a little on a piece of metal. Twenty per cent. of lump asphalt is then to be added to the tar and stirred in until the lumps are melted. Then it is allowed to cool and can be kept for use.
For making black varnish that has a gloss, fuse three pounds Egyptian asphaltum; when it is liquid add one-half pound shellac and one gallon turpentine.
A black varnish for steel and iron is made by boiling together sulphur and turpentine. Upon evaporation of the turpentine a thin layer of sulphur is left, which is united with the iron when heated a short time over a gas or spirit flame.
(2) For a good black varnish for covering iron work, etc., use 48 pounds of asphaltum; add 10 gallons of boiled oil, red lead and litharge 7 pounds each, dried and powdered white copperas 3 pounds. Boil for 2 hours; then add 8 pounds dark gum amber (fuse), 2 gallons hot linseed oil; boil for two hours longer or until a little of the mess when cooled may be rolled into pills, then withdraw the heat, and afterward thin down with 30 gallons of oil of turpentine.