Delta metal is an alloy of zinc, iron and copper, to which, during fusion, phosphorus is added, and then, according to the use it is to be put, further additions of tin, lead and manganese. This metal has the color of a gold-silver alloy, and can be worked either hot or cold. You cannot weld it, and it is soldered with difficulty. It does not rust. A common composition of this metal is as follows: Copper, 55 82-100 per cent.; lead, 76-100 per cent.; manganese, 1 38-100 per cent.; iron, 76-100 per cent.; nickel, 6-100 per cent.; zinc, 41 41-100 per cent.
To discover lead in tin, a small bit of tin is detached and put into a watch glass, with a drop of nitric acid and two or three drops of water; the glass is then gently heated over a flame, and when the solution is complete a few drops of water and a concentrated solution of iodine of potassium are added, when, if lead is present, a yellow precipitate will be the result.
Brighten the surface of the article to be tested by filing, and apply a drop of nitric acid. Allow the acid to work for a few minutes, then wipe same off and rinse with water. If the metal be wrought iron, a dead white or ash-gray spot can be seen. If cast-iron, a deep black one. If steel, a brownish-black one.
A new process for enameling cast-iron objects, in which the principle is adopted that the enamel will take better on white than on gray iron, as the latter contains a quantity of free carbon (graphite). Sulphur is used in casting which will unite and form sulphuret of carbon, and the iron is covered with a skin of white iron where exposed to the action of the sulphur. Ready-made objects are painted over with sulphuric acid of 60 degrees Fahr., and then heated, by which means the acid in the pores acts on the graphite in a similar manner.
The formula consists in treating the castings with dilute hydrochloric acid, which dissolves a little of the metal, and leaves a skin of homogeneous graphite holding well to the iron. The iron is then washed in a receiver with hot or cold water, or cooked in steam, so as to remove completely the iron chloride that has been formed. Finally, the piece is allowed to dry in the empty receiver, and a solution of india rubber or gutta percha, in essence of petroleum, is injected, and the solvent, afterwards evaporated, leaves a hard and solid enamel on the surface of the iron work. Another plan is to keep the chloride of iron on the metal instead of washing it off, and to plunge the piece into a bath of soda silicate and borate. Thus is formed a silico-borate of iron, very hard and brilliant, which fills the pores of the metal skin. As for the chlorine disengaged, it continues with the soda to form sodium chloride, which remains in the pickle.
Ironware is enameled with porcelain by first cleaning the surface free from moulding sand, then heating the article in an oven to a low red in the dark, or what is called a black heat, to slightly oxidize the surface and free it from grease. Then brush the powdered enamel mixed with water, and dry quickly. Then bake with a red heat. For the second, or finishing coat, brush on the glazed coat and treat as the first. For the first coat make a mixture of 66 parts calcined flint ground to a powder. 34 parts borax. Melt these together and pulverize, then add 12 parts potter's clay. Mix the whole with water to the consistency of paint, and apply. For the glaze coat take 15 parts borax, 73 parts powdered glass, 12 parts soda. Mix and melt, then pulverize and apply with water. Bake at a red heat.