ADHESION. That property possessed by bodies of dissimilar natures of resist ing a force applied to separate them ; and it differs from cohesion and affinity. Adhesion cannot occur between two solid bodies, for then the force which binds them together is either some modifica tion of the attractive force, or it is due to atmospheric pressure : for perfect adhe sion, one of the bodies ought to he fluid or semifluid ; it may afterwards return to the solid condition without destroying the adhesion, unless it crystallize. It is desirable also that they should not con tract unequally in cooling, for then the adhesion would be destroyed : for the union of two surfaces into one it is there fore necessary that both should contract equally : and cement for uniting different surfaces depends for its fitness upon this property : to cement metals with other solids, solders are needful, and particular solders for various metals. Such bodies as pitch, which even at reduced tempera tures will expand, are those which ad here most firmly. The adhesion between solid bodies is sufficiently strong to over come the cohesive force of one of them es when two pieces of wood are glued together and then separated forcibly, a layer of glue remains on each piece. The adhesion of the wafer on the envelope is greater than the cohesion between the particles of the paper, and a layer comes off on the surface of the wafer when the latter is separated. When a solid dips
in a liquid, its adhesion is sometimes greater than the cohesion for the parti cles of the liquid, as when wood or metal is dipped into water the water adhering is said to wet it. Wood or the finger, dipped into quicksilver, is not wetted. Oils have no adhesion for water. (For other instances of adhesion, see CEMENT.) ADZE-A DDICE. A cutting chisel with an arched blade and the edge at right angles to the handle it differs from the chisel in application, the force being impact and arising from a blow and ,not that of mere pressure. The adze cuts the wood, if its edge be fine ; but if not, the wood is split and the tool acts then more like the axe as a wedge than the chisel. In coarse preparatory work, the adze is carried through the space be tween the workman two feet, and the quantity of wood removed is very great ; in fine work, the foot is placed upon the wood and the adze is carried two or three inches under the sole, and the smooth ness and delicacy of the work accom plished is surprising.