Although glue is much used by the joiner it is seldom so by the carpenter, but as some knowledge of its strength and mode of application may be useful, the following information is given.

To ascertain the strength of common glue Mr. Bevan obtained two cylinders of dry ash, each 1 1/2 inch in diameter and about 8 inches long, which he glued together end to end. After being allowed to rest for twenty-four hours, he found that they required a force of 1260 lbs. to separate them; and as the area of the surface in contact was 1.76 square inch, it follows that a force of 715 lbs. would be required to separate one square inch. The glue used in this experiment was fresh made, and the season very dry.

In some former experiments made by Mr. Bevan during the winter season, and with glue which had been frequently melted with occasional additions of fresh glue and water, he found a result of 350 lbs. to 560 lbs. to the square inch. The present experiment was made with great care, and every precaution taken to ensure that the direction of the force passed the centre of the surfaces in contact.

The pressure was applied gradually, and was sustained for two or three minutes before separation took place. Upon examining the separated surfaces, the glue appeared to be very thin, and did not entirely cover the wood, so that the actual cohesion of glue must be something greater than 715 lbs. to the square inch.

* ' Repertory of Arts, etc.,' second series, vol. xxvii., p. 314.

The lateral cohesion of a piece of board cut out of Scotch fir, which had been quite dry and seasoned, was 562 lbs. to the square inch. Therefore if two pieces of this board had been well glued together, the wood would have yielded in its substance before the glue.

The cohesion of a piece of solid glue, or the force required to separate one square inch, Mr. Bevan found to be 4000 lbs.*

Good glue in the cake is very hard, and appears clear and partly transparent when held before the light. It swells in water on being steeped, but does not readily dissolve.

To prepare glue it should be broken into small pieces and steeped in the water for about twelve hours; it should then be submitted to a gentle heat until it becomes sufficiently dissolved for use.

When it is required to glue up work, the parts which are to receive the glue should be made perfectly clean and smooth, and the wood should be thoroughly dry, the glue should also be applied as hot as possible.

The strength of common glue for coarse work is increased by the addition of a little powdered chalk. Skimmed milk in the proportion of 1 lb. of glue to 2 quarts of milk is sometimes used to dissolve glue with the view of increasing its capability of resisting moisture.

Marine Glue is made of 1 part of india-rubber, 12 parts of mineral naphtha or coal-tar, gently heated and mixed, to which is afterwards added 20 parts of powdered shellac. It is then poured out on a slab to cool. In using, it must be heated to about 250°. A good glue for outside work is sometimes made by grinding as much white-lead with linseed oil as will just make the liquid of a whitish colour and strong but not too thick.

* 'Phil. Mag.,'1826.