ADHESION OP GLUE. Mr. Bevan glued together by the ends, two cylinders .of dry ash wood, one-fifth of an inch in diameter, and about 8 inches lost'.
After they had been glued together twenty-four hours, they required a force of 1260 lbs. to separate them; and as the area of the circular ends of the cylinders were 1.76 inch, it follows that the force of 715 lbs. would be required to separate one square inch. It is proper to observe, that the glue used in this experiment was newly made, and the season very dry; for in some former experiments on this substance, made in the winter season, and upon some glue which had been frequently made, with occasional additions of glue and water, he obtained a result of 350 to 500 lbs. to the square inch. The present experiment was, how ever, conducted upon a larger scale, and with care in the direction of the resultant force, so that it might be, as near as practicable, in a line passing at right angles through the centre of the surfaces in contact. The pressure was gradually
applied, and was sustained two or three minutes before the separation took place. Upon examining the separated surfaces, the glue appeared to be vefy thin, and did not entirely cover the wood, so that the actual adhesion of glue must be something greater than 715 lbs. to the square inch. Upon comparing with this, the natural cohesive force laterally of wood of the same kind, Mr. Bevan found it to be only 562 lbs.: consequently, if two pieces of this wood were well glued together, the wood would have yielded in its substance before the glue. From a subsequent experiment made on solid glue, the cohesive force was found to be 4,000 lbs. per square inch ; from which it may be inferred, that the application of this substance as a cement is susceptible of improvement.