Читать книгу Henley's Formulas, Recipes and Processes (Applied Chemistry) - Various - Страница 272

—When silver is alloyed with copper only one proportion is known which will give a uniform casting. The proportion is 72 per cent silver to 28 per cent copper. With more silver than 72 per cent the center of a cast bar will be {76} richer than the outside, which chills first; while with a less percentage than 72 per cent the center of the bar will be poorer and the outside richer than the average. This characteristic of silver-copper alloys is known to metallurgists as “segregation.”

When nickel is added to the silver and copper, several good alloys may be formed, as the following French compositions:

	I	II	III
Silver	33	40	20
Copper	37–42	30–40	45–55
Nickel	25–30	20–30	25–35

The whitening of alloys of silver and copper is best accomplished by annealing the alloy until it turns black on the surface. Cool in a mixture of 20 parts, by weight, of concentrated sulphuric acid to 1,000 parts of distilled water and leave therein for some time. In place of the sulphuric acid, 40 parts of potassium bisulphate may be used per 1,000 parts of liquid. Repeat the process if necessary.