Platinum and steel, equal parts by weight, form a beautiful alloy, which takes a fine polish, and does not tarnish. This alloy is said to make the best speculum. Steel, for edge tools, is improved by this metal. The proportions, which appear to be most proper, are from one to three per cent. An alloy of 10 platinum with 80 of steel, after exposure for many months, had not a speck on its surface. Would not this alloy, as it is not oxidized, be very useful for making points for lightning rods, in lieu of iron, gold, silver, or platinum alone? The experiment is worth a trial; for nothing adds more to the safety of a magazine, or building, against the effect of lightning, than a conductor.
Iron and carbon, it appears, are capable of uniting in different proportions; hence the variety of crude iron, and the different kinds of steel. When the carbon exceeds the iron, as in plumbago, or black lead, it forms a carburet. When the iron exceeds, such compounds are properly speaking sub-carburets; under which name, we may rank all the varieties of cast iron and steel.
The hardness of iron, according to the experiments of Mushet, (Phil. Mag. xiii, p. 138), increases with the proportion of charcoal, with which it combines, until the carbon amounts to about 1/60th of the whole mass. This is the maximum, the metal acquiring the colour of silver. More carbon diminishes the hardness, according to its quantity. The difference in iron, whether it be the cold-short, or hot-short iron, a matter of some consequence to the workers in this metal, was found to be owing to phosphoric acid in the cold-short, which exists with the iron. But the substance, called siderum by Bergman, is a phosphuret, and not a phosphate of iron.
We have gone into this subject more fully, on account of its importance, and intimate connection with the casting of guns, and the different qualities of iron. In fire-works, it will appear obvious, that the various properties exhibited by iron are owing to the iron and carbon, to the changes which they undergo, to the combustion which necessarily ensues, and to the production of oxide of iron, and carbonic acid gas; effects that invariably take place, whether cast iron or steel be used, provided it is exposed to the action of agents, under the same circumstances and conditions.
Sec. XLVII. Of Glass.
Glass, in the form of powder or dust, is used in fire-works. The pulverization of glass is easily performed. It may be done in an iron mortar, and passed though fine wire or brass sieves. It is used in the composition for wheels, in water balloons, cones, fire-pumps, slow white fire, &c.
Glass is nothing more than fused silica, made by exposing a mixture of silica and other substances to the action of a violent heat.
The quality of the glass depends on the proportion of silica, and the fluxes which are used in promoting its fusion; for the various kinds of glass, as white glass, green glass, bottle glass, &c. are all, in one respect, the same, though they differ in these particulars.
The glass of Saint-Gobin in France is made by fusing white sand, lime, soda, and broken inferior glass. The white goblet-glass is made of sand, potash, lime, and old glass; the quantity of potash is about fifty per cent. If green, or yellow, the colour is destroyed by the addition of black oxide of manganese; and hence that oxide is named glass makers' soap.
The common plate glass, for electrical machines, &c. is formed of sand, crude soda, old glass, and oxide of manganese. The bottle glass, made with the soda of marine plants, consists of sand, soda, common ashes, and old glass. Another bottle glass is made by melting common sand, black or yellow, with soda, wood-ashes, clay, and broken glass. It appears from the use of the substances which enter into, and compose, glass, that its quality is owing to the materials employed. The crystal or flint glass is a finer kind. The substances, with the proportions in which they are used, are the following: