This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
For an account of glue, its qualities, characters, etc., the reader is referred to ' Workshop Receipts,' second series, pp. 78-84, in which full details are given for soaking, boiling, and otherwise preparing the adhesive solution. Glued surfaces need to be forced into the closest possible contact, so that there shall intervene the slightest possible film of the adhesive substance; and there is no point upon which amateurs make greater mistakes. A thick wad of glue does not stick 2 pieces of wood together, but keeps them apart. If we could plane 2 boards perfectly true, so as to exclude even a film of air, they would adhere without glue. But this is not possible. Nevertheless, we make some approach to such condition when, having planed both approximately level, we insert the thinnest possible layer of some adhesive substance - in this case glue - and press them into the very closest contact that we can. The bulk of the glue is squeezed out, and is to be wiped off; but after all is squeezed out that is possible, a sufficient film will remain to give the necessary adhesion; and supposing the glue of good quality and properly applied, the closest union of the parts will be found to take place.
The glue should be applied quite hot; and in cold weather it is well to warm the joint before applying the glue, if the character of the work will allow it. With very thin stuff this warming is not advisable, as the fire will warp the wood. A convenient " glue-brush," according to Cowan, may be made from a piece of rattan cane, having the outside crust pared off, and the end dipped in boiling water and hammered out till the fibre is well separated. It is described as the best, cheapest, most durable, and most effective means of applying glue.