Kenneth Barton Jr., age 15, of Austin, Tex., for his question:
WHEN WAS GLUE FIRST USED?
Glue is a substance that is used as as adhesive. The word comes from the Latin verb "gluere," which means 'to draw together." Paintings on the walls of a tomb in southern Egypt show glue being used in veneer work more than 3,000 years ago.
Glue has been used is China for a long time. It has also bean used in India for centuries to make India ink and to disperse lampblack and carbon black is water.
Glue is an organic material that is made by heating properly prepared bones, sinews and hide or skin fragments in water and drying the resulting solutions.
When glue is being manufactured commercially, the hot diluted solutions are filtered, clarified and then evaporated. The concentrated "liquors" can then be dried on drum dryers or in spray dryers.
A more common method of manufacturing glue is to allow the solutions to chill to firm jellies. The jellies are then cut into thin slices, which are spread out on nets. Stacks of these nets are next run on wheeled carriers into drying tunnels against a current of warm air.
In the drying tunnels the temperature is low at first to avoid melting the jelly. But as a "skin" forms on the surface and the stacks approach the hot end of the dry room, the temperature rises.
Commercial glue, when in cake or broken flake form, will show marks of cotton or galvanized iron nets on which it was dried.
Glue is generally sold in granulated form, called ground glue, as a convenience in handling and as a better way to prepare it for use. The final color may be from light to dark yellow or brown, but some glues are whitened by the addition of zinc oxide.
Since glues can quickly decay, preservatives are added.
To prepare dry glue for use, it is soaked in water and then heated.
Because the essential meaning of "glue" is "that which sticks together," any products of adhesive nature are called "glue" when they are not actually so.
Sodium silicate solutions are often called "mineral glues." Vegetable gum and dextrin solutions are called "vegetable glues." Solutions of rubber, pitch and asphalt, which are waterproof, are called "marine glues." And fine water proof adhesives made from modern synthetic resins or plastics also are galled "glues." Paste used to stick paper together is not "glue" either.
The main uses of true glue are for wood joints and veneers is furniture, pianos, house trim, barrel heads, coffins and toys. It is also very important in bookbinding sad In the making of paper boxes, gummed paper and cloth tapes, match heads, dolls' heads and printer rollers.
The abrasive grains on sandpapers, garnet and emery papers are held on by glue.