Henley's Twentieth Century Formulas, Recipes and Processes. VariousЧитать онлайн книгу.
so far exceeds this.
Pewter.
This is an alloy of tin and lead only, or of tin with antimony and copper. The first is properly called pewter. Three varieties are known in trade:
I (Plate Pewter).—From tin, 79 per cent; antimony, 7 per cent; bismuth and copper, of each 2 per cent; fused together. Used to make plates, teapots, etc. Takes a fine polish.
II (Triple Pewter).—From tin, 79 per cent; antimony, 15 per cent; lead, 6 per cent; as the last. Used for minor articles, syringes, toys, etc.
III (Ley Pewter).—From tin, 80 per cent; lead, 20 per cent. Used for measures, inkstands, etc.
According to the report of a French commission, pewter containing more than 18 parts of lead to 82 parts of tin is unsafe for measures for wine and similar liquors, and, indeed, for any other utensils exposed to contact with food or beverages. The legal specific gravity of pewter in France is 7.764; if it be greater, it contains an excess of lead, and is liable to prove poisonous. The proportions of these metals may be approximately determined from the specific gravity; but correctly only by an assay for the purpose.
Silver Alloys:
Aluminum Silver.
—Aluminum and silver form beautiful white alloys which are considerably harder than pure aluminum, and take a very high polish. They have the advantage over copper alloys of being unchanged by exposure to the air, and of retaining their white color.
The properties of aluminum and silver alloys vary considerably according to the percentage of aluminum.
I.—An alloy of 100 parts of aluminum and 5 parts of silver is very similar to pure aluminum, but is harder and takes a finer polish.
II.—One hundred and sixty-nine parts of aluminum and 5 of silver make an elastic alloy, recommended for watch springs and dessert knives.
III.—An alloy of equal parts of silver and aluminum is as hard as bronze.
IV.—Five parts of aluminum and 1 part of silver make an alloy that is easily worked.
V.—Also aluminum, 3 parts, and silver, 1 part.
VI. Tiers-Argent.—This alloy is prepared chiefly in Paris, and used for the manufacture of various utensils. As indicated by its name (one-third silver), it consists of 33.33 parts of silver and 66.66 parts of aluminum. Its advantages over silver consist in its lower price and greater hardness; it can also be stamped and engraved more easily than the alloys of copper and silver.
VII.—This is a hard alloy which has been found very useful for the operating levers of certain machines, such as the spacing lever of a typewriter. The metal now generally used for this purpose by the various typewriter companies is “aluminum silver,” or “silver metal.” The proportions are given as follows:
| Copper | 57.00 |
| Nickel | 20.00 |
| Zinc | 20.00 |
| Aluminum | 3.00 |
This alloy when used on typewriting machines is nickel-plated for the sake of the first appearance, but so far as corrosion is concerned, nickeling is unnecessary. The alloy is stiff and strong and cannot be bent to any extent without breaking, especially if the percentage of aluminum is increased to 3.5 per cent; it casts free from pinholes and blowholes; the liquid metal completely fills the mold, giving sharp, clean castings, true to pattern; its cost is not greater than brass; its color is silver white, and its hardness makes it susceptible to a high polish.
Arsenic.
—Alloys which contain small quantities of arsenic are very ductile, have a beautiful white color, and were formerly used in England in the manufacture of tableware. They are not, however, suitable for this purpose, on account of the poisonous character of the arsenic. They are composed usually of 49 parts of silver, 49 of copper, and 2 of arsenic.
China Silver.
—Copper, 65.24 per cent; tin, 19.52 per cent; nickel, 13.00 per cent; silver, 2.05 per cent.
Copper-silver.
—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.
Copper, Silver, And Cadmium Alloys.
—Cadmium added to silver alloys gives great flexibility and ductility, without affecting the white color; these properties are valuable in the manufacture of silver-plated ware and wire. The proportions of the metals vary in these alloys. Some of the most important varieties are given below.
| Silver | Copper | Cadmium | |
|---|---|---|---|
| I. | 980 | 15 | 5 |
| II. | 950 | 15 | 35 |
| III. | 900 | 18 | 82 |
| IV. | 860 | 20 | 180 |
| V. | 666 | 25 | 309 |
| VI. | 667 | 50 | 284 |
| VII. | 500 | 50 | 450 |