Cohesion, or Attraction of Cohesion, is that power by which the particles of bodies are held together. The absolute cohesion of solids is measured by the force necessary to tear them asunder; heat is excited at the same time. At the chain cable manufactory of Capt. Brown, a cylindrical bar of iron, of 11/2 inches diameter, was drawn asunder by a force of 43 tons. Before the rupture the bar lengthened about 5 inches, and was reduced nearly three-eighths of an inch at the part where the fracture took place, which became heated to a degree unpleasant, if not painful, to the hand. The cohesive force of metal is considerably increased by hammering, rolling, or drawing. The following table shows the cohesive strength of a square inch in lbs. avoirdupois, or the force necessary to pull asunder a square inch of the various substances named therein.

Cohesion 375

lbs.

Copper,cast......................

22,000

Ditto, wire......................

61,000

Gold wire......................

31,000

Iron, cast......................

30,000 to 50,000

Ditto (German)......................

68,000

Ditto, bar......................

60,000 to 80,000

Ditto (German)......................

60,000 to 90,000

Ditto, wire......................

113,000

Platinum wire......................

56,000

Silver ditto......................

40,000

Ash............................................

17,000

Beech......................

17,000

Deal (Norway spruce)................

18,000

Ditto (English)......................

7,000

Elm........

13,000

Oak........

11,000 to 16,000

Hemp fibres glued together .

92,000