Glue which exhibits a bad odour when moistened should be rejected and used only for making size, and for uniting the coarser varieties of articles; and when the glue-pot begins to exhibit any signs of putrefaction, it ought to be carefully cleaned out and thoroughly soaked and washed, for the presence of a little bad glue will soon destroy a whole batch of a good article.

The preparation of glue demands care rather than skill. In dissolving glue, it is best to weigh the glue, and weigh or measure the water. If not done there is a liability of getting more glue than the water can properly dissolve. It is a good plan, when once the quantity of water that any sample of glue will take up has been ascertained, to put the glue and water together at least 6 hours before heat is applied, and if not soft enough then, let it remain longer in soak, for there is no danger of good glue remaining in pure water, even for 48 hours, provided the weather be cold; but it must not be allowed to lie too long in that liquid, or it will begin to decay, especially in warm weather. To meet this difficulty, and secure the quick soaking of the glue, there has of late years been introduced a pulverized or granulated article which is excellent. Frozen glue, made porous by freezing, is also used with this object in view. After being soaked, the glue should be melted, great care being taken that it be not burned. Next to putrefaction, burning is the great destroyer of glue. Burnt glue is always weak. If kept dry, glue may be preserved for any length of time; but when once moistened, even the best samples soon spoil.

No more glue should be prepared at any one time than is to be used immediately, and whenever a job requiring extra strength is to be executed, it will always pay to prepare a fresh lot. Formerly, when glue was generally heated over the naked fire, the old-fashioned glue-pot was always used This pot is double - the space between the outer and inner vessels being filled with water. Consequently where this pot is employed, the glue can never be made hotter than boiling water, and thus all danger of burning is avoided. Now that more delicate and convenient modes of heating have been devised, this old pot has in some cases been dismissed, to the evident deterioration of the process. Even steam should never be employed except to heat water in the outer case. In applying glue, it should be remembered that the thinner the layer which is applied the stronger will be the joint, and the less water there is combined with the glue the sooner will it dry, and consequently the less will the joint be exposed to accidental disturbance before union has fairly occurred.

Carpenters should remember that fresh glue dries more readily than that which has been once or twice melted.

If glue is of first-rate quality, it can be used on most kinds of woodwork very thin, and make the joint as strong as the original, but it is necessary that the glue be brought into intimate contact with the entire surface of the wood.

A drop of melted glue allowed to simply fall on a surface of dry, cold wood and dry there, will often fail to adhere at all, while if the same drop had been rubbed in, it would have attached itself to the surface with wonderful tenacity. In applying glue, therefore, we must secure this perfect contact, and we must also employ every means in our power to delay the gela-tinization of the glue until the joint has been completed. The glue should therefore be used while very hot, as hot as it will bear, and in very cold weather the wood itself should be warmed. The glue should be well rubbed in with a stiff brush and the two surfaces should be rabbed well together and retained in contact under great pressure until the glue has become somewhat dry. Complete dryness rarely takes place under several days; but after the lapse of 12 hours, the joint becomes tolerably strong. A joint made in this way is probably as strong as can be made by any ordinary process. (Phin.)

Holding Power Of Glue

From numerous experiments, Dr. Karmarsch has arrived at the following conclusions: -

1. Glue exerts a far greater hold on surfaces of wood cut across the grain than on those that have been split or cut with the grain.

2. Where two surfaces of split wood are laid together, the hold of the glue is the same, whether the fibres are laid parallel or crosswise to each other.

3. The holding power of glue on different woods, estimated in kilogrammes per square centimetre, is as below: -

Cut across the grain.

Split.

Beech .. ..

155.55

7883

Hornbeam...

126.50

79.16

Maple..

87.66

63.00

Oak......

128.34

5516

Fir .. ..

, 110.50

24.16

(Moniteur Indust. Beige.)

How To Prevent The Cracking Of Glue

When articles that have been glued are exposed to great beat, they are often much damaged by the cracking of the glue. This evil may be avoided by adding to the glue chloride of lime, which is a very soluble salt, and prevents the glue from drying so as to become brittle. Glue so prepared adheres firmly to glass, metal, etc, and may be used for sticking on tickets so as not to come off. (Pharm. Zeitsch. of Russia.)

Application

The preparation of glue is very simple. It is first broken up into small pieces and put into a vessel, covered with cold water, and left to soak for a number of hours, the length of time required for soaking being generally governed by the strength of the glue, the strongest glue taking the longest time. After being soaked until it all swells and becomes soft and gelatinous (avoid over-soaking), it is placed upon the fire to cook, being kept stirred until it is thoroughly dissolved and appears stringy. It is then ready for use; but in factories where a large quantity Is employed, it is then poured out in a large flat pan and left to cool; and the workman, when desiring it for use, cuts off the required quantity and heats it. It is a bad habit for workmen to allow the glue-pot to remain on the stove after they have done with it, as a very prolonged heat will destroy the adhesive qualities of the glue. Glue, to resist well a damp atmosphere, should contain as little saline matter as possible. When buying the article, venture to apply your tongue to it, and if it tastes salt or acid reject it for any but the commonest uses. The same operation will also bring out any bad smell the glue may have.

Those are very simple and ready tests, and are the usual ones by which dealers and large consumers form their judgment. Another good test is to soak a weighed portion of dry glue in cold water for 24 hours, then dry it again, and weigh. The nearer it approaches to its original weight, the better glue it is, thereby showing its degree of insolubility. Glue loses much of its strength by frequent re-melting. Therefore, glue which is newly made is preferable to that which has been re-boiled. The hotter the glue the more force it will exert in keeping the joined parts glued together. In all large and long joints it should be applied immediately after boiling. Apply pressure until it is set or hardened.

In applying glue, where the part is end grain, first fill the pores of the wood with thin glue, and let dry; then clean off, and glue it at the joint with strong glue. Many a job has been spoilt by reason of neglecting to fill the end grain in this manner. In adding water to glue, it is best to give the glue a boil before using again, so that it may be evenly and thoroughly mixed.

Quick Drying Glue

Put your glue into a bottle 2/3 full, and fill up with common whisky; cork tight, and set by for 2 or 3 days, and it will dissolve without the application of heat, and will keep for years. (For manufacture of glue, see article Gelatine.) 2

Lapland Glue

The bows of the Laplanders are composed of two pieces of wood, glued together. One of them is of birch, which is flexible, and the other of the fir of the marshes, which is stiff, in order that the bow when bent may not break, and when unbent it may not bend. When these two pieces are bent, all the points of contact endeavour to disunite themselves, and to prevent this the Laplanders employ the following cement: They take the skins of the largest perches, and having dried them so that the greasy part may be removed by scraping and wiping, and the oil soaked out by any porous material, they soak them in water until they are so soft that they may be freed from the scales, which are thrown away. They then put 4 or 5 of these skins in a reindeer's bladder, or they wrap them tip in the soft bark of the birch tree, in such a manner that water cannot touch them, and place them thus covered in a pot of boiling water with a stone above them* to keep them at the bottom. When they have boiled about an hour, they take them from the bladder or bark, and they are then found to be soft or viscous, like strong glue. In this state they employ them for gluing together the two pieces of their bows, which they strongly compress together and tie up until the glue is well dried.

These pieces never afterward separate.