TENACITY (from the Latin tenacitas," the power of holding "), a property of material bodies by which their parts resist an effort to force them asunder.
This property is the result of the corpuscular forces acting within the insensible spaces supposed to exist between the particles of bodies; It is consequently different in different materials, and in the same material it varies with the state of the body with respect to tempera ture and other circumstances.
Those corpuscular forces consist of attractions which vary according to unknown laws with the distances of the particles from one another, and even at certain distances they become repulsions [ATTRACTION] ; but in all bodies except the elastic fluids, the combined actions of all the particles produce that coherence which constitutes the tenacity of the masses. In those fluids the particles have no coherence, and when the pressures to which they are subject are removed, those particles immediately separate from each other with forces depending, probably, upon the quantity of caloric with which they are combined. In non elastic fluids and in solids, tenacity exists, but in very different degrees; Its force depending upon differences in the intensity of the attracting powers between the particles, upon differences In the distances of the particles themselves, upon the action of the caloric, and, in some cases, upon variations in the pressure of the atmosphere.
The molecules of liquids adhere to one another, and generally to those of solid bodies, by attractive forces which decrease very rapidly ; and, at Insensible distances from the supposed places of contact, the adhesion entirely disappears [CAPILLARY ATTRACTION) the real tenacity of the molecules being, as Dr. Young observes, equal to the excess of their mutual attractions above the forces of repulsion arising from the actions of the calorific particles. It is on account of the small distance to which the attractions of the fluid molecules extend, and to the freedom with which the particles move on one another, that fluids appear to have so little tenacity; bnt from the weight of water :support in gleam tubes, Dr. Robison has estimated that the mutual attractions of the particles of water on a surface equal to one square inch must far exceed 190 pounds.
(Inane of duet or Nand, while dry, have no power of adhering toge ther, probably because their forms do not permit a sufficient number of points on their surfaces to be Lrought within the distance at which corpuscular attractions take place ; but, if slightly wetted, the mutual attractions between the (lust and the liquid produce a certain degree of tenacity. This la very sensible in clay moistened with water ; for, being then drawn into the form of a rod, it is capable of bearing a small weight suspended from it. Tenacity exists in various degrees in viscid fluids, as oil, gum dissolved In water, &c. Sealing-wax and glass also, when heated, lose their brittleness, and acquire plasticity, whereby they become capable of being moulded into any form, while their par ticles retain a considerable degree of adhesive power.
The tenacity of solids constitutes, in part, the subject of tho power of bodies to resist strains; and under MATERIALS, STRENGTH OF, will be found a table of the weights which would overcome the force of cohesion in rods immoveably fixed at one end and pulled in the direc tion of their length. Those weights may be considered as the measures of tenacity in the different kinds of material ; and it may be added that, from a mean of several experiments made by Telford on the tenacity of forged iron, the breaking strength, when reduced to that which it would be if the area of a transverse section of the bars had been one square inch, is 293 tons. The bars were cylindera or paral lelopipeds varying in length from 1 foot 5 inches to 2 feet 3 inches, and in area of section from 0.56 to 3.14 square inches : they stretched in length from two inches to four inches before they broke. Telford found, also, that a bar of cast-steel bore, suspended from it, 27.92 tons, a bar of blistered steel tons, and of cast-iron (Welsh pig) 7/6 tons ; the area of the section in all being one square inch. Tenacity in solid bodies varies greatly with their temperature. Coulomb took a piece of copper-wire, which, when cool, carried 22 lbs. suspended from it ; and, upon bringing it to a white heat, it would scarcely bear 12 lbs.