J. A. Taggart

“ An important aid to cleanliness is the use of copper, aluminum or brass for all [Pg 59] parts of the apparatus with which glue comes into contact. Not only are copper, aluminum and brass the cheapest materials to use in the long run, due to their resisting acids in glue, water and steam which quickly corrode iron, but copper, aluminum and brass are practically self-cleaning.
Iron equipment is especially bad. It is most expensive in the end, for iron is quickly eaten away by acids in glue and water. Iron rusts, and the rust impairs the color and quality of the glue liquid. ”

“ America now produces glue of excellent quality to meet practically all requirements. So great are the requirements that almost the entire amount of the American-made glue is absorbed by the home demand. ”

“ A very thin piece of good glue will bend without breaking. When it does break, if the edges are splintery, great tensile strength is indicated. A clean fracture, on the other hand, indicates a brittle, low-grade glue, which has been subjected to heat so long as to destroy the tissue; or else it has been made from bone stock. High-grade glues never show glassy fractures, but bone glues do. In making this test, the air conditions of the room should be taken into account. If the glue has been kept in a dry room it will naturally break much more readily than if it has been in a moist atmosphere. ”

“ Whatever injures and breaks down these fibres inevitably weakens the glue; so that in melting, every care must be observed to avoid the breaking down of the glue-fibres.
The most common destructive agent is heat. Just as the application of heat breaks down the fibres of a roast of beef, rendering it “tender” as the saying is, so the prolonged application of heat, or heat of too great an intensity, will destroy the glue-fibres, and therefore radically impair their value for actual use. ”

“ Bone glues are usually darker than hide glues, but some bone glues go through an artificial clarifying process which gives them the appearance of high-grade glues but really detracts from their strength. Very frequently oxide of zinc is added to glue, the effect being to make it set quickly, as well as to give it a light color. Some glues contain so much oxide of zinc that they are milk-white. Zinc oxide is not harmful except when added in very large quantities. ”

“ A further vital objection to the use of steam direct is that the steam contains [Pg 54] acids from boiler compounds, dirt, pipe-rust and sediment, all of them injurious to the strength and to the elasticity of glue.
Then too, glue always takes up moisture from steam. This changes the consistency of the glue. It leads to guess-work. The quantity of water added to glue must always be exactly regulated. Turning live steam on glue prevents proportions of glue and water remaining constant. ”

“ As glue deteriorates quickly if allowed to stand, no more should be prepared than is needed for a single day’s work. It is even better to prepare it twice or oftener during the day.
If glue is dissolved at the proper temperature and kept at that same temperature after melting, no noticeable deterioration results during the course of the working day. But if allowed to stand over night its value decreases, and it should not be mixed with fresh glue, as it is not of the same consistency. ”

“ The facts already mentioned about the melting of glue should be borne in mind in choosing a glue melter, or glue-heater—always remembering in particular that it is of utmost importance that the heating agent should not come into direct contact with glue, and that the glue should not be overheated in preparation. ”

“ Up-to-date practice in all the larger concerns using glue demands a laboratory for making tests. An expert is put in [Pg 41] charge and the glue analyzed chemically as well as for its physical properties. This method cuts the guess-work down to a minimum. Manufacturers whose output would not permit the employment of an expert all the year round can have glue analyzed in laboratories maintained for such purposes. It means often a great saving of money in the end to learn the exact properties of the glue you propose to use, or that you may be actually using. ”

“ The term “boiling,” or “cooking,” never should be applied to the process of glue melting. These words imply a temperature of 212° F.—and such a temperature is ruinous to glue. In producing glue from the original stock—from the hides, bones, sinews, etc.,—boiling is necessary, in order to extract the gelatinous matter—but as we have already seen, the longer the stock is boiled, the weaker the product. “First boilings” are always best. ”

“ When a wood is being used that is strong in acid it is advisable to use a glue containing enough oxide of zinc to neutralize the acid in the wood. In making sizing for paper a glue containing either acid or alkali in excess should be avoided. It is also held by some authorities that acid in glue tends to bring about decay. ”

“ The cost is less than either steam or gas and its advantages are so great that thousands of institutions are now using these “fireless” glue-heaters. The best electric glue-heaters are made of copper and brass, the greatest conductors of heat. They require much less heat than any other pot and the heat is required for just about one-fifth the time, owing to the heat-retaining jacket. ”

“ By noting the working qualities of glue prepared with various proportions of water, you can determine what is the correct amount of water to use, and then by using the hydrometer as each batch is prepared, you can be sure that the correct proportions are always being used. By making readings from time to time with the hydrometer, you can also determine the amount of evaporation that is going on, and in this way guard against the glue becoming too thick for proper use. ”

“ Not only overheating of the glue is prevented, but expense of supervision is reduced. The heater does not need to be constantly watched for fear glue will not be kept at correct temperature.
This particular heater is also provided with a brass agitator (hand or power) for keeping glue thoroughly mixed while melting, and with a special faucet by means of which the melted glue is drawn off without dripping or clogging. It is made in sizes from 2 gallons to 500 gallons liquid capacity, and for use with any heating agent—gas, electricity, or steam. ”

“ The outer covering, in which the wool, fur or hair is rooted, is of no importance to the glue-maker. The portion that produces the glue lies next to it, being composed of fibres which run in every direction and contain the fluid matter which aids in keeping the skin moist and pliable. The fat cells are directly beneath the glue-yielding portion, and as fat is undesirable, because it makes the glue greasy, the shreds of fat are saponified by being subjected to a lime bath. ”

“ Yet some glue-rooms still use the old open glue-pot, and many others use apparatus which shows little, if any, improvement.
Modern glue-room appliances are now available for every glue-room, for every [Pg 66] purpose. No glue user, large or small, can afford to use any but modern, scientific equipment. The saving in time, and in materials, and in improved quality of the completed work, and in the greater respect and increased efficiency of workers in the glue-room, all these things result in quickly repaying the increased outlay required. ”

“ Dirt enters the melting-pot through the glue itself, the introduction of dirty brushes, or the exposure of the pot to dust, etc. If glue is melted in a dirty pot, the skin forming on the surface of the glue liquor gradually accumulates at the sides of the kettle and slowly decomposes. ”

“ Glue is used in the wood-working industry mainly for making joints and veneers.
In large establishments, where many workmen are employed, a good plan for [Pg 77] distributing the melted glue is to arrange a battery of small glue-pots, or warmers, strung along a pipe line running from the steam boiler or gas heater.
Individual pots of copper which are filled at the central source of supply fit into cast-iron jackets, kept warm by steam which comes from the pipe line. The requisite temperature is thus maintained at minimum cost. ”

“ Bubbles may appear within the glue—not on the surface—without being an indication of putrefaction. As a matter of fact, bubbles are practically always found in certain high-grade glues, though practically never in low-grade bone or hide glues. They are supposed to be due to the air which gets in when the glue is poured into the moulds. When glue is originally dried on nets in very cool and dry weather, such bubbles are frequently found. Always beware of glue showing surface bubbles. ”

“ The only safe procedure in melting glue is to use a thermometer. If glue is melted in an open pot, or one in which the contents of the glue chamber can be reached easily, an ordinary drop thermometer, encased in a frame for protection, may be used. ”

“ Glue-room equipment of iron is still sold, but only because there are still some users who are so blinded by the initial small saving in outlay, as not to see the saving that accrues in the end from using indestructible materials—and the additional saving due to good work and economy of glue. ”

“ By the use of the automatic temperature controller the temperature is kept at the proper point, and there is no necessity of making observations with the thermometer except to verify your controller.
The temperature controller not only permits the scientifically correct preparation of glue, preventing overheating and ruined work, but saves also in expense of supervision. ”

“ A great deal of waste in the use of glue is due to evaporation. If glue is heated in open pots, evaporation is very great. Evaporation weakens glue; makes it too thick for use, and also makes it very uneven in quality. Glue should always be melted in a closed vessel. ”

“ The drying is a source of concern to the manufacturer. It is extremely important to keep the temperature at just the right point, to protect the glue from dust and dirt, and to avoid the possibility of bacterial growth in the glue-jelly, which is very susceptible to the development of harmful organisms. ”

“ In soaking and thinning glue, use only pure, cold water. Unless heater is provided with pure water attachment or pure water chamber, avoid using water from the glue-heater. Do not use water from boilers, for such water contains pipe-rust, acids from boiler compounds, sediment, and other matter extremely harmful to glue. ”

“ Besides being free from bubbles or blots a good glue is smooth, though not necessarily glossy. Sometimes the very best glue will be of a dull color, and many inferior glues even have a very shiny surface. ”

“ Since 1837, in which year Peter Cooper, who may justly be regarded as the founder of the glue-making industry in the United States, produced the first American-made glue, the yearly output has steadily increased. ”

“ Between two or more glues of any one type, actual experiment is the only safe guide. Most glue men will give you good advice; but above all, keep accurate records of results of the different grades used. When you have found the right glue, keep to it. ”

“ The tanneries supply most of the hide stock, but only waste pieces reach the glue manufacturer, as leather is more valuable than glue, and the larger portion is therefore reserved for the tanner’s use. ”

“ The keeping property of glue may be determined by letting the glue-jelly stand for several days exposed to the air, and noting any deterioration. It is customary to let the jelly stand at room temperature—but if the glue is to be kept under any special conditions the test should be made as nearly under these conditions as possible.
ODOR
Deterioration is always accompanied by a sour odor. Avoid using any glue that does not smell clean and sweet. ”

“ Sizing—Use a glue free from grease and foam and one that flows freely.
Paper Boxes—A quick-setting hide glue is indicated for setting-up. For covering, a lower test bone glue is preferred, as it does not set so quickly. Paper box manufacturers are troubled more or less with foaming glue and can use the remedy suggested in the paragraph on veneers, as this will not be objectionable in paper box work. ”

“ The soaking of glue in cold water before using is employed in some factories as a basis for comparative test of working quality. The amount of water absorbed may vary as much as 10 ounces in half a pound. ”

“ In selecting a veneer press equipment the amount of pressure per square inch must first be determined. Opinion varies with different manufacturers, some using 100 pounds, some 200 pounds, per square inch. The best general results are obtained by using 150 pounds per square inch. All presses made with a 2-inch screw should be designed to withstand a pressure of 8 tons or 16,000 pounds per screw. ”

“ Pressure should be distributed as evenly as possible. Presses may be had in almost every style for every need—open on one side, or on two sides; for veneered stock; sectional presses; etc. Very excellent presses are being made of structural steel. They are practically indestructible, very efficient, and yet simple in operation. ”

“ Glue should be heated slowly, requiring about 30 minutes. Rapid heating dissolves the outer portions of the glue quickly, and a scum is then formed over the rest of the glue, preventing its proper melting. ”

“ No glue is good to use unless properly prepared. A 16-cent glue may be reduced to the grade of an 8-cent glue by overheating. [Pg 83] The grade of the glue at the time it is used is the important thing. ”