ADHESION, is the property by which two solids, a solid and a fluid, two solids and an interposed fluid, or two fluids, remain attached to each other when their surfaces are brought into contact. It is a property of much im portance in machinery, since friction depends upon it to a considerable extent. M. Guyton de 3Iorveau found by direct experiments, that when the surfaces of plates of different metals were placed in contact with the surface of mercury, the weights required to separate' them from the fluid were as stated in the fol lowing table (the metals were pure, the plates circular, one inch diameter, and of equal thicknesses) Grains. Grains.
Gold . . . 446 Zinc . . . 204 I Silver . . . 429 Copper . . 142 Tin . . . 418 Antimony . 126 I Lead . . . 397 Iron 115 Bismuth . . 372 Cobalt . . 8 . . 282 • Mr. Bevan has given a table of the adhesion, &c. of different kinds of nails when driven into dry Christiana deal ; in this table it appears that a sixpenny nail, 73 to the lb., 21 inches long, forced 1i inches into the wood, required 327 lbs. weight to extract it ; the percussive force required to drive the sixpenny nail to the depth of one inch and a-half into the dry deal, with a cast-iron weight of 6.275 lbs., was
four blows or strikes falling freely, the space of 12 inches, and the steady pressure to pro duce the same effect was 400 lbs. With different kinds of timber the results varied greatly, and Mr. Bevan concludes that a six penny nail driven two inches into dry oak, would require a force of more than half a ton to extract it by steady pressure. Mr. Bevan has also determined the force required to draw screws out of different kinds of wood ; the screws used were about two inches in length, .22 diameter at the exterior of the threads, .15 diameter at the bottom, the depth of the worm or thread being .035, and the number of threads in one inch 12. These screws were passed through pieces of wood, exactly half an inch in thickness, and drawn out from the following dry woods by the an nexed weights : beech 460 lbs., another spe cimen 790 lbs., ash 790 lbs., oak 760 lbs., ma hogany 770 lbs., elm 655 lbs., sycamore 830 lbs. The force required to draw similar screws out of deal and the softer woods, was about half the above.