670
THEORY AND PRACTICE OF ENGINEERING.
Rook II.
ployed for the process, and iron plates so covered are extensively used for roofing, and donot after many months exhibit any signs of decay. The iron being coated with zinc in acold solution does not in any way change its condition ; but when the zincing of iron isperformed, by steeping it in a bath of melted zinc, a combination takes place between thetwo metals, and a brittle alloy is the consequence, the iron losing all its tenacity.
Tin is usually prepared from the native oxide, its oxygen being removed by charcoal: thepurer kinds are called grain tin, and the others block tin. The common ores are knownunder the name of mine tin, and furnish a less pure metal than the stream tin. Tin has asilvery white colour; its specific gravity is 7*3, and air and moisture have little effect uponit: it melts at 442°, and is converted into a white oxide by exposure to heat and air.
The specific gravity of the native peroxide of tin is 7*, and its primitive crystal an obtuseoctohedron.
Protoxide of Tin .* specific gravity 6*6 : —
Tin -
_
-
- 1
.
58
-
87*8
Oxygen
-
-
- 1
-
8
-
12*2
1
66
1000
Bisulphuret of Tin , (A/trum musivum, Mosaic Gold,} is a mixture formed by heating per-oxide of tin, which contains two of oxygen and one of tin, with its weight of sulphur.Bisulphuret of tin is also formed by decomposing pcrchloride of tin by sulphuretted hydro-gen ; it is quite insoluble in the acids, except nitro-muriatic ; it forms the bronze powderused by paper-stainers.
The weight of a cubic foot of cast tin is 455 ’7 pounds, and the weight of a bar 12 incheslong and an inch square is 3*165 pounds ; it expands, accoiding to Smeaton, at one degreeof heat 75^, and melts at 442°. It will bear on a square inch 2880 pounds without anypermanent alteration, and an extension of length of -j^g. Compared with cast-iron, itsstrength is 0*182 times, its extensibility 0*75 times, and its stiffness 0*25 times, cast-ironbeing considered as unity.
Copper is found native, and of its ores the most remarkable arc the oxide, sulphuret, sul-phate, carbonate, chloride, arseniate, and phosphate. It has a red and brilliant colour, ismalleable and ductile, melts at a dull white heat, or at 2548°, and in oxygen gas burns witha green light; when long exposed to moist air a green crust of the carbonate is formedupon its surface. The weight of a bar 12 inches long and 1 inch square is 3*81 pounds, andits length is increased by one degree of heat ^^5. Its specific gravity is 8*8, and the cohe-sive force of a square inch is 33,000 pounds when hammered. Copper is principally pre-pared from the native sulphuret of copper and iron, which is heated with a flux of charcoaland siliceous matter ; the sulphur is first expelled, and the metals oxidated ; the oxidatediron forms a slag with the flux, and the charcoal reduces the oxide of copper. When theore is broken, it is heated in another reverberatory furnace, where it is fused, and the re-mainder of the slag removed from it, when it is cast into pigs, which are again broken upand melted with a portion of charcoal. 'Hie metal is rendered malleable by constantlystirring it when in the furnace with a pole of green wood, and it is afterwards cast intocakes 18 inches by 12, the weight of a cubic foot of which is 549 pounds.
Oxide of Copper is black, insoluble in water, but with acids forms coloured salts.
Copper
-
-
- 1
-
32
80
Oxygen
-
-
- 1
-
8
20
1
40
100
Sulphate of Copper (Blue Vitriol ) is formed by dissolving peroxide of copper in dilutedsulphuric acid ; its crystals are of a fine blue colour, and in rhomboidal prisms. The com-mon blue vitriol is obtained by exposing roasted sulphuret of copper to air and moisture,but it is often impure, from the iron and zinc it contains. When animal substances are im-bued with it and dried, they* remain as it were preserved, and it has been employed in astate of solution to immerse timber for the purpose of preventing the dry rot. The crys-tallised sulphate of copper contains
Oxide of copper
-
- 1
40
32
Sulphuric acid
-
- 1
40
32
Water
- 5
1
45
125
36
100