Quadrant of the meridian 6214.413 miles.

One degree of the terrestrial meridian is 69.049 miles.

One degree of longitude on the equator equals 69.164 miles.

A degree of longitude upon parallel 45 equals 48.988 miles.

A nautical mile equals 1.153 statute miles and is equal to one minute of longitude upon the equator.

Length of a pendulum beating seconds in vacuum at sea level at New York is 39.1012 inches.

Length of a pendulum beating seconds in vacuum at the equator is 39.01817 inches.

Mean distance of the earth from the sun is 95,364,768 miles.

Time occupied in transmission of light from the sun to the earth is 8 minutes, 13.2 seconds.

Trautwine gives the holding power of 6 d nail driven one inch into oak as 507 pounds; beech, 667 pounds; elm, 327 pounds; pine (white), 187 pounds; 3% inch square spike driven 41⁄2 inches into yellow pine, 2000 pounds; oak, 4000 pounds; locust, 6000 pounds; 1⁄2 inch square spike in yellow pine, 3000 pounds; 16 square spike six inches in yellow pine, 4873 pounds. In all cases the nails or spikes were driven across the grain. When driven with the grain the resistance is about one half.

*Heat at which scale forms and adheres, i.e., does not fall away from the piece when allowed to cool in air.

1725

1825

1975

2200

Iron Ores

Iron is usually found as an ore in one of the following classifications, oxides, carbonates and sulphides.

The following table gives the subdivisions of these classes and an idea of the general composition and character of the different varieties.

In the presence of manganese, chromium, etc., hard carbides (double carbides) are formed, known as cementite.

A mixture of ferrite and cementite is called pearlite.

Pearlite often consists of alternate layers of ferrite and cementite and in this condition, from its peculiar iridescence, is termed pearlite. As carbon increases, ferrite is replaced by pearlite.

Pearlite is not found in hardened steels.

In steels saturated with carbon, a point fixed by Professor Arnold as .89 per cent carbon, the whole structure is represented by pearlite.

Steels containing less than .89 per cent carbon are known as unsaturated; those having over .89 per cent carbon as supersaturated. These degrees refer distinctly to iron-carbon steels; for the double carbides the point of saturation is slightly lowered.

Cementite is a hard and brittle compound, but when interspersed with ferrite in the form of pearlite, its brittleness is somewhat neutralized by the adjacent ferrite.

A steel containing well laminated pearlite possesses high ductility but less tenacity than when found unsegregated.

Pig Iron

Pig iron contains from 92 to 96 per cent metallic iron; the remainder is mostly composed of silicon, sulphur, phosphorus and manganese in greatly varying amounts. Cobalt, copper, chromium, aluminum, nickel, sodium, titanium and tungsten appear in some brands in minute quantities.

Specific gravity of cast iron is variously given at 7.08, 7.15 and 7.40.

Latent heat of fusion, 88 B.t.u.*

Total heat in melted iron, 450 B.t.u.

Critical temperature, 1382° F., Stupakoff.

Coefficient of linear expansion for 32° F., 0.000006.

The usual practice of furnaces has been to grade by fracture.

The grades are designated, Nos. 1, 2, 3, 4 or gray forge; mottled and white.

No. I. Soft; open grain; dark in color. castings. Does not possess much strength;

Used for thin, light has great softening

properties; is mixed advantageously with harder grades; carries large percentage of scrap.

No. 2. Harder, closer, stronger and color somewhat lighter than No. 1. No. 3. Harder, closer, stronger and lighter in color than No. 2; and inclines to gray.

No. 4 (Gray forge). — Hard, strong, fine grained and light gray color. Mottled. - Hard, very strong and close grained. Color presents mottled or imperfectly mingled gray and white colors.

White. - Hard and brittle, breaks easily under sledge but has high tensile strength; color white.

No. 1 iron running in the spout of the cupola displays few sparks. In the ladle its surface is lively and broken, sometimes flowery.

Nos. 2 and 3 present similar appearances but less marked.

Hard irons running from the cupola throw out innumerable sparks; in the ladle the surface is dull and unbroken; if disturbed the reaction is sluggish.

One cannot safely be guided by the appearance of the fracture of the pig; as when melted it may produce a casting of an entirely different character than that indicated.

* Harker and Oberhoffer have found that the specific heat of iron increases in about the same ratio up to within the region of the critical point (1382° F.). After this it remains practically constant.