CHEMURGIC CORPORATION 4. Book I MODERN GLUES AND GLUE TESTING (Other than Waterproof Glues) BY CLYDE H. TEESDALE, A. B. Formerly in charge, Section of Wood Preservation, Forest Products Laboratory, Madison, Wisconsin With an Appendix Methods of Testing Animal Glues at the Forest Products Labo- ratory, Madison, Wis., in which is set forth the standards of the Bureau of Aircraft Production, U. S. Army Published By THE PERIODICAL PUBLISHING CO. GRAND RAPIDS, MICHIGAN Copyrighted by The Periodical Publishing Co. Grand Rapids, Michigan 1922 2031745 PREFACE When the United States entered the great war and it became necessary to build airplanes by thou- sands, very definite specifications and satisfactory methods of testing glues were sorely needed. The problem of developing specifications and methods of test was turned over to the Forest Products Labora- tory and was worked out under my direction. This book is based largely on the results that were obtained, and which were applied in practically all purchases of glue during the war by both the Army and Navy Departments. General information on the manufacture and use of glues is given, and a description of the methods of testing that are described in the literature on the subject. Acknowledgement is made to Mr. A. T. Deinzer of Monroe, Mich., who contributed valuable information used in compiling this book; also to Mr. Geo. M. Hunt of the Forest Products Laboratory for valuable suggestions and criticisms and for contributions to parts of the text, and to Mr. L. J. Markwardt, Mr. A. C. Knauss, and Mr. Wilbur Lloyd Jones, of the Forest Products Laboratory, for contributions to the text. THE AUTHOR. BOOK I TABLE OF CONTENTS CHAPTER I General Discussion (Earliest Record of Glues) Distinction between Glues and Gelatine General Process of Animal Glue Manu- facture Resulting Variation in Properties Deter- mination The Peter Cooper Grades 11 CHAPTER II Miscellaneous Glues Fish Glues Liquid Glues Vegetable Glues Casein Glues Blood Albumin Glue Silicate of Soda 15 CHAPTER III Uses of Glue- Paper Paper Boxes Books Straw Hats Wall Paper Matches Leather Goods and Belting Textiles Writing Tablets Woodworking 19 CHAPTER IV Glue Testing (Preliminary) Preliminary Examination Absorption of Moisture from the Air Appearance Selecting of Samples Surface and Other Bubbles Odor Gloss Color Fracture Foam "Keeping" Qualities 23 CHAPTER VGlue Testing Evidence of a Single Test not Conclusive Moisture Ash Acidity Grease Water Absorption Melting Point 27 CHAPTER VI Viscosity Types of Viscosimeters Engler Viscosimeter the U. S. Government Standard Viscosity Determination at U. S. Forest Products Laboratory Value of Viscosity Test .. 31 CHAPTER VII Jelly Strength The Finger Test Lipowitz Test Edmund S. Smith Testing Apparatus Jerome Alexander Value of Jelly Strength Test 37 8 MODERN GLUES AND GLUE TESTING CHAPTER VIII Strength of the Glued Joint Joint Tests Indicate Quality of Workmanship Rather than Glue Strength Selection of Woods for Glue Tests Variation in Application of Glue and Manufacture of Joint Application of the Load The Spandau Test- British Royal Aircraft Test Aeronautical Inspection Directorate (England) Method Shear Test and Ten- sion Test A Widely Used Method Discarded at Madi- son, Wis. The Forest Products Laboratory Shear Test A Modification of Madison Standard Test Miscel- laneous Tests Plaster Rod Test Setterburg Test Gill Test 41 CHAPTER IX Plywood Strength Test Equipment and Method Adopted as Standard at the Forest Products Laboratory, Madison, Wis 57 CHAPTER X Specifications Bureau of Aircraft Production, U. S. Army Specifica- tion for Handling and Testing Hide Glue U. S. Gov- ernment Standard Specification for Hide Glue Certified in Airplane Construction 63 CHAPTER XI Results of Tests on Miscellaneous Glues.... 71 CHAPTER XII Grading the Glue Sample Jerome Alexander and Peter Cooper Grades Compared Table of Viscosities and Jelly Strengths for Alex- ander Standard Grades 77 CHAPTER XIII Some Interesting Strength Data on Glues Woods that give Strong Joints Scratched Joints versus Smooth Joints Laminated Construction Re- sistance of Animal Glues to Moist Air 81 CHAPTER XIV Use and Application of the Glue Hydrometer 85 APPENDIX. Methods of Testing Animal Glue at the Forest Prod- ucts Laboratory, Madison, Wis., 1919 Standards of the Bureau of Aircraft Production, U. S. Army 87 CHAPTER I. GENERAL DISCUSSION IT is said that glue has been known and used for thirty-three hundred years. Furniture found EARLIEST in tombs of the ancient Egyptians of the period RECORD OP of the Exodus was dovetailed, and joined with glue and GLUES. nails. Romans, of the time of Cicero, were familiar with glue, and it was in extensive use in England during the reign of Queen Elizabeth. The term glue is used in its broadest sense to de- note an adhesive. Used in this sense it includes a great variety of substances. The oldest and best known of these is animal glue. Animal glue comes in an almost infinite variety, due to the differences in methods of manufacture and the source and quality of the materials used. Glues or adhesives are also produced from starches, casein, blood albumin and sodium silicate. In general, animal glue is a substance akin to gela- tine, though not identical with it, and is produced from the bones, sinews, hides, etc., of animals. It is difficult DISTINCTION to define the difference between glue and gelatine be- BETWEEN cause these substances may be very similar in their GLUES AND composition, appearance and properties. Gelatine, GELATINE. however, is usually used for purposes in which absence of taste, odor and color, together with a firmness of jelly are desired. It is often used in foods. Con- sequently it is prepared from selected materials free from decomposition. Glue, on the other hand, is usually used for its adhesiveness, and lower grade materials and less care may be employed in its pro- duction. It is rather important for a glue user to have a clear idea of the difference between glue and gelatine and of the method of manufacture of glue. A true conception of this may cause him to change his methods of glue handling. The frequently heard state- ment that gelatine is a pure form of glue is not strictly correct. Neither glue nor gelatine occurs as such in 12 MODERN GLUES AND GLUE TESTING GENERAL PROCESS OF ANIMAL OLUE MANUFACTURE. VARIATIONS IN METHODS OF MANUFACTURE. nature. They are formed by heating certain animal tissues in the presence of water. The action is chemical, not simply one of solution. A portion of the water molecule, according to recent ideas, combines chemically with the animal matter, the technical term describing the action being "hydrolysis." This action proceeds rapidly at a high temperature, and slows down as the temperature is lowered. Hence both time and temperature are important factors in glue making. As the action proceeds, a series of products is formed, each one differing slightly from the one from which it was produced. While neither glues nor gelatines are produced in this way commercially, we may consider, for our purpose, that the first one formed is gelatine. Continued action produces first very strong viscous glue, then weaker and weaker glues, until finally, if the action is continued long enough, a product is obtained that will not form a jelly when cold, and which has no adhesive properties. It makes no difference whether the heating occurs in the glue maker's boiler or in the wood user's shop room. When- ever the glue is heated in the presence of water, chemical action occurs which steadily reduces the quality of the product.* The process of making animal glue is, briefly, as follows: The stock is washed and treated to remove dirt and grease, then boiled to convert the glue-form- ing substances into a glue solution, which is concen- trated by evaporation until it will form a jelly on cooling. The jelly is then dried and the resulting product is the glue. There are many details and variations in the steps above outlined which depend upon the kind of stock used and the plant in which the glue is made, all of which have more or less effect upon the character of the resultant glue. For instance, bones are sometimes boiled without first removing either dirt or grease. This naturally fails to produce a high-quality glue. It is common practice to treat bones with acid to remove the calcium salts before cooking, but this is not always done. In cooking, the temperature and time have to be *See Rideal (Glue and Glue Testing), page 10. GENERAL DISCUSSION 13 carefully watched, as over-cooking may materially re- duce the strength of the glue. The stock is usually boiled several times, using fresh water each time. .The first boiling or first run gives the best glue, the strength of the glue obtained from the succeeding boilings being less each time. Sometimes two or more boilings from the same kettle, or boilings from dif- ferent kettles, are mixed together or "blended" before the liquor is concentrated. The solution of glue from the boiling kettles is too weak to form a jelly which can be handled, so it must be concentrated. This is done by boiling off the water in vacuum pans until the percentage of glue in the solution is high enough to make a firm jelly on cooling. If the temperature gets too high during the con- centrating process the quality of the glue may be lowered. When sufficiently concentrated the glue solution is METHODS OF cooled by refrigeration, either after being run into COOLING. pans or as it runs upon a traveling belt. As it cools it forms a jelly firm enough to handle. The jelly in the pans is removed, sliced with wires or a knife, and placed upon screens to dry. If a belt is used the jelly is formed in a continuous sheet, which is cut into sec- tions and placed on screens as it travels along. The screens are then placed in a drying chamber and left until the glue is dry. The glue may be easily injured during the drying process if the temperature condi- MISCELLANEOUS tions are not properly controlled. The form of the FORMS. OF glue when dry depends upon the shape in which it was GLUE - placed upon the screens. If carefully sliced to the proper thickness regular shaped cakes will be formed. The sheet glue from the belt breaks into thin irregular shaped pieces as it comes from the drying nets. This is commonly run through a machine to break it into smaller pieces, in which shape it is shipped as flake glue. Other miscellaneous forms of glue are also made, and any of them may be subsequently ground and sold as ground glue. Sometimes mineral matter such as barium sulphate, white lead, chalk, or whiting is added to the glue after it has been concentrated, but before it is cooled. 14 MODERN GLUES AND GLUE TESTING This gives it a light color and makes it opaque, which is a feature desired by some consumers. From the above very brief description of various steps in the manufacturing process it can readily be seen that the variety in character, color, fornj, strength, etc., of glues can be almost without limit. PETER COOPER A system of classification, based chiefly on the jelly GRADES. strength, was devised a long time ago by Peter Cooper, by which it is possible to group the great variety of glues into a relatively few classes or grades. The grades established by Cooper, beginning with the strongest, were designated, respectively, A Extra, 1 Extra, 1, IX, 1*4, 1%, li/ 2 , 1%, % 17/ 8 , 2. There are now glues stronger than A Extra, and glues weaker than 2, for which there is no standard Peter Cooper grade. This system of grading, however, ap- pears to be but little used today by manufacturers, except sometimes for comparative purposes. Each manufacturer has his own system of grading which he keeps more or less secret, and to the general buying public the grades mean little or nothing. It is some- times claimed also that the Peter Cooper grades of today are not the same as those established long ago. CHAPTER II. MISCELLANEOUS GLUES FISH glue is made from the skins, bones, bladders, etc., of fish. The finest grades are made from the swimming bladders, and come on the market FISH in the product known as isinglass. It is said that fish GLUES. glues can be made that are practically equal in ad- hesiveness to hide or bone glues. Liquid glues are marketed in liquid form ready for use. Most glues are so prepared that they can be used cold. They are quite popular and have a large sale. Usually they are higher in price than ordinary LIQUI1 animal glues. They may be prepared by special treat- G1 ment of hide or bone glue, but very often they are made from fish glues. In recent years vegetable glues have been used in increasing quantities, especially for gluing veneers. At the start of the war the price of animal glue soared, and forced a very wide use of vegetable glues, STARCH especially in the veneer trade, where the use of animal GLUES. glues was practically eliminated. The commercial im- portance of vegetable glue is now obvious to practically every large user of glue. Most vegetable glues are made from starch and alkali. Some consumers seem, however, to be suc- cessfully gluing with starch boiled in water, without the addition of alkali. The most commonly used veget- able glues are produced from cassava flour and caustic soda (sodium hydroxide). During the war the short- age of shipping facilities prevented the importation of cassava flour, and much potato starch was used, usually where possible in mixtures of as much of the cassava flour as possible. Corn starch has been used. POTATO STARCH Other materials than caustic soda, such as tri-sodium G phosphate, sodium carbonate, etc., have been used. Sometimes the starch is treated with sulphuric acid (hydrolized or processed) before mixing with the alkali. The best qualities of vegetable glues, when properly made, show strength properties which com- 16 MODERN GLUES AND GLUE TESTING pare favorably with the medium to good grades of animal glues. They also have certain advantages of use, especially that of applying cold, that are well known to most of our readers. Vegetable glues are often criticised because of their rather common prop- erty of staining wood. Recent work indicates that this difficulty is being overcome. The Perkins Glue Company, well known manufac- turers of vegetable glue, made the following state- ment: PERKINS "Vegetable glue is manufactured by taking a car- GLUE. bohydrate such as cassava flour, the water absorptive property of which has been decreased or is already sufficiently low, but not too low, and mixing therewith the necessary small amount of water and dissolving the starch in the water by stirring in a solvent such as caustic soda, whereby a viscous, colloidal semi-fluid glue is formed having substantially the properties of animal glue for veneering. Some heat may be used in making the solution, in which case the amount of alkali used may be decreased." Ordinary glues were not equal to the demands of war time airplanes, and as a result the development of waterproof glues, especially for veneer parts of air- planes, received a tremendous impetus during the war. WATERPROOF The successful airplane waterproof glues were all made CASEINS AND either from casein or blood albumin. The wide use of BLOOD ALBUMIN these glues in the industries will without doubt result GLUES. after the war in their widespread adoption for in- dustrial purposes. Not only may they replace bone or vegetable glues for some purposes, but they make pos- sible the use of veneered and built-up wood products in exposed locations, formerly not possible because of the lack of a suitable glue. Casein glues in general are made from ground casein, calcium hydrate (slaked lime), and some form of caustic soda. Sometimes sodium silicate or sodium phosphate are used. Blood albumin glues are made usually from black soluble blood albumin, calcium hydrate, with a small quantity of sodium silicate, sodium hydrate, or ammonia. Often casein is mixed with the blood albumin. Casein glues set hard when MISCELLANEOUS GLUES 17 cold, and are consequently termed cold glues. They may be used in cold press equipment. Blood albumin glues depend upon the application of heat to coagulate the albumin, and hence require heated presses for their application. Silicate of soda is successfully used as an adhesive in the paper box industry. There is a widespread WATER feeling that it may some day be used to advantage in GLASS. certain lines of wood work. Without doubt the very low cost of silicate of soda makes it an attractive material with which to experiment, and the results thus far obtained are promising. The Bureau of Plant Industry, United States Department of Agriculture, has patented an adhesive CORN OOB produced by boiling corn cobs in water under pressure. ADHESIVE. The resultant solution is concentrated and used as an adhesive. The product is not as yet developed to a commercial success, but gives great promise of suc- ceeding as a substitute for sodium silicate in the paper box industry. It is said that it will be lower in cost than sodium silicate. CHAPTER III. USES OF GLUE GLUE is used in. a great variety of industries, aside from its use in joining wood. Among these may be mentioned paper sizing, where its purpose is to make the surface of paper less porous, or to give it "glaze." Animal glue, gelatine and casein are used, dependent to some extent on the relative market costs and availability at the moment, and upon the quality of the product being made. Glue for sizing paper is usually bone glue, of high PAPER grade, free from foam, light in color, and containing SIZE. no more than the normal amount of grease. It should show no perceptible odor after heating a solution in water at 100 F. for 100 hours. Alum is sometimes added to this glue by the paper manufacturer to make a free flowing solution. Paper box makers prefer a quick setting hide glue PAPER BOX for "setting up." For "covering" a slow setting bone ADHESIVE. glue is used. Mixtures of animal glues with vegetable glues are often used, one advantage being lower cost. Here a product is required that is strong, flexible BOOK and free from color and odor. BINDING. Straw hat manufacturers desire a hide glue free from lime, color and odor. In wall paper, freedom from grease and objection- able odor is desired. In match making, uniformity is desirable. The glue is used in combination with phosphorous to assist in preventing atmospheric oxidation of the phos- MISCELLANEOUS phorous. For leather goods and belting, flexibility, tenacity and resistance to moisture are the desirable qualities in glue for leather and belting. High grade hide glues with linseed oil and glycerine added in small amounts are often used. Glycerine is said to increase flexibility, and linseed oil, resistance to moisture. 20 MODERN GLUES AND GLUE TESTING JOINING WOOD. HIGH GRADE GLUE MAY BE THE MOST ECONOMICAL. USED IN Glue is used in dressing and finishing colored yarns TEXTILES. and threads, sizing of worsted and woolen wraps, and in the printing of fabrics. High grade hide glues free from odor and color are required. Tons of glue are used for writing tablets. Almost any grade, except the very poorest, will answer. A glue is valued primarily for its power of resist- ing rupture. This includes absence of brittleness, and it should have the power of yielding or stretching slightly before it ruptures. Glues may be found which are very strong if the strain is applied steadily, but which break under the impact of a suddenly applied load. A weaker b,ut more elastic sample is superior to such a glue for joining wood. In general however, a glue may be valued on a basis of its strength proper- ties. Intimately related to the strength property is the covering capacity of glue. Its value is largely con- trolled by these two factors. High strength usually is accompanied by great covering capacity, and hence higher priced glues may actually cost less to use than lower priced ones, which require more glue to ac- complish the same purpose. Covering capacity is re- lated to three factors the water absorption, the jelly strength, and the viscosity of a solution of known strength. These tests made with accuracy will usually give a close indication of the grade or the value of a glue. Color is important in some lines of wood work, being especially undesirable in high grade furniture. As a rule, however, a dark color should not be con- sidered detrimental, as absence of color may represent high cost or the use of undesirable and weakening chemical bleaching agents. KEEPING Keeping qualities are of some importance. Alkaline QUALITY OF glues are more liable to spoil or decompose, due to GLUES. bacterial action, than acid glues. Hence a test for acidity and alkalinity give an indication of keeping properties. Glues made from partly decomposed stock do not keep well, and have a bad odor when the glue solution is heated. Hence odor has a bearing on keep- ing qualities. USES OF GLUE 21 A recent development is the use of glue as a filler in automobile tires. The lower grades of bone glue that formerly went largely to the veneer trade, are preferred. This new use of glue is of tremendous im- AUTOMOBILE portance to the animal glue industry, especially in view TIRES - of the inroads made on their market by vegetable glues. At the present time, only a few tire concerns are using glue, but the demand from this source promises to expand to very large proportions. CHAPTER IV. GLUE TESTING (PRELIMINARY) A UNIFORM and generally adopted method of testing glue has never been developed, due largely to the variable and uncertain chemical composition of glue. It is exceedingly desirable for GLUE TESTING glue users to test their glues rather than trust wholly REQUIRES A to the promises of the salesman. The technique of SKILLED glue testing requires a trained observer and good OPERATOR. equipment to accomplish very much, though there are a few simple tests and observations that can be made by any one and which will give some idea of quality. Chemical analysis of glue does not enable one to select glues according to quality, and has never been successfully applied. Glue testing consists largely of physical tests, such as viscosity, jelly strength, strength of the glued joint, ash, moisture, odor, etc. War made necessary the development of methods of testing and specifying glue, and centered the attention of experts in this kind of work on the glue testing problem, not only in the United States, But in the European countries. The glue testing methods selected by the warring countries were naturally the best avail- able, and hence are worthy of the most serious con- sideration of any reader interested in this subject. One of the most successful attempts thus far made to GLUE TESTING develop a uniform practice of glue testing was ac- SCIENCE complished in the United States, where all glues for ADVANCED BY airplanes for both the army and navy was given a THE WAR - most thorough inspection. This work was done at the Forest Products Laboratory at Madison, Wis. Inten- sive investigation by a large force over several months on methods of testing was carried out under the guid- ance of a glue chemist of national reputation. All of the testing methods that might seem to have any merit whatsoever were tried. The resultant methods TESTS BY AN selected in this way were incorporated in a tentative AUTHORITY. specification which was submitted to a conference of glue manufacturers, and as finally evolved, had the 24 MODERN GLUES AND GLUE TESTING SOME SIMPLE BUT SUPERFICIAL TESTS. SIGNIFICANCE OF COLOR. approval of all. They may therefore be considered as the best that this country has developed thus far. In the following pages a few simple tests will be outlined that are possible to make without great ex- perience or complete equipment. The more refined tests, however, require a trained analyst, familiar with the manipulation of testing apparatus, and a well equipped laboratory. The methods of test recom- mended by the Forest Products Laboratory are men- tioned in outline only in the text, but are grouped together and given in full in the appendix. Glue should not become damp or sticky (hygro- scopic) in the air, or it may mold. A hygroscopic glue indicates adulteration with sugar, molasses, etc. The appearance, hardness and manner of breaking are points which may be used to judge quality after some experience. Some glues may have a cloudy or milky appearance, due to the presence of calcium phosphate. Glues of excellent strength may be warped or twisted, and very dark in color. Ground glue should not lump together in warm, humid weather. Samples should be taken from several parts of the package, as glues are very often blended from more than one run and the mixing may not have been thorough. Special attention should be given ground glue, which is very easy to adulterate. White bubbles on the surface of the glue are an indication of decom- position. With such samples be sure to test the odor, as described later. Decomposed or sour glues are to be avoided. Bubbles appearing deep in the glue are not necessarily an indication of putrefaction. An expert glue buyer is able to judge somewhat by ex- amining a flake of glue by looking through it at a strong light. Gloss on the surface does not necessarily indicate high quality. On the contrary, low grade glues may be highly glossed, while good quality glues may be dark, though the surface should be smooth. A uni- form color and surface appearance is desirable. Color is not a reliable indication of quality. The first runs of glue from the glue stock are lighter in color than the last ones. But it is easy to clarify glues GLUE TESTING (PRELIMINARY) 25 chemically, greatly weakening them in the process. Bone glues are usually darker than hide glues, unless they have been bleached. With any particular lot, non- uniformity of color indicates either adulteration or blending. The addition of zinc oxide gives a white opaque glue, and one that sets quickly. It is also said to add somewhat to its water resistance. In moderate quantities zinc oxide is not injurious. Sometimes inert matter of no value is added as an adulterant. Hence the color of such samples may well be reason for suspicion. Breaking a sample of the glue with the thumb and SIMPLE TEST forefinger of each hand gives an indication of glue FOR QUALITY. quality. The condition of the air must be considered, as a dry day will give a different indication than a humid one. If the glue fractures evenly and bends but little, low strength and brittleness are indicated. If a thin sheet bends well and in case it breaks, shows a splintery fracture, good strength is indicated. Bone glues show a glossy fracture ; hide glues of high grade never do. Foam in a glue is undesirable. A solution of glue in water may be stirred vigorously, with a rod, or better, with an egg beater, and a fair indication of its foaming properties will be obtained. Particular atten- tion should be paid to the rate at which the foam sub- sides. If it persists for long, the glue should be avoided. Odor is a sign of poor keeping quality. Usually ODOR SHOULD offensive odor is the result of using spoiled or de- BE SWEET. composed stock, or else it may mean that the glue itself has started to decay. Something may be learned by smelling of a moistened flake of glue warmed in the hand. A more reliable method is to heat a solution of glue in water, about 1 part glue to 12 of water, at a temperature of 100 for 48 hours. It should remain sweet during this period. A similar sample should be able to stand at room temperature for four or five days without de- veloping a bad odor, or showing the presence of mold or decomposition. CHAPTER V. GLUE TESTING* WHILE the tests just described are useful guides in purchasing glue in the absence of better methods, they are, at best, a makeshift. Wherever possible advantage should be taken of more TESTg ARE refined methods. MISLEADING. The reader should, however, have a rather clear idea of the limitations of glue testing. It is usually not possible to obtain a very clear idea of glue value from any single test that may be applied. In an article describing the testing and grading of glues, the follow- ing statement is made by E. G. Clayton (Jour. Soc. Chem. Ind., 1902, 21, 670) : "In conclusion, the observations seem to show that while it would be rash to form a judgment on glue from a single test, the evidence afforded by a number may be irresistible. The expert's surest system ap- pears to be not to rely on single short cut tests of general quality, but to employ a number of methods, including any having especial bearing on the pros- pective or present uses of the glue, and then to base his conclusions on a consideration of all the results together." Ordinary glue of good quality contains from 8 to 16 per cent, of water. Too much water indicates poor MOISTURE keeping quality, and of course means that the buyer D is paying for that much water. Too little water may indicate an over-dried glue, which is injurious to its strength properties. Moisture as low as 5 per cent, is not uncommon, but a good glue should have not less than 8 per cent. Moisture is determined by heating a ground sample at a temperature of 110 C. to a constant weight. The sample being hygroscopic, must be cooled in a desiccator. After making the moisture determination, the DETERMINATION same sample may be used for determining ash. It *See Appendix for Forest Products Laboratory methods. 28 MODERN GLUES AND GLUE TESTING REACTION* TO LITMUS. INSOLUBLE. WATER ABSORPTION*. should be incinerated carefully in platinum, or pre- ferably in vitreosil, care being taken to prevent free ignition. The ash usually varies from 11/2 to 3 per cent. A fused ash indicates a bone glue, one not fused a hide glue. A large ash indicates adulteration, and a chemical examination will show what it is. Calcium phosphate is found in the ash of bone glues. By its reaction to litmus a glue shows whether it is acid, alkaline or neutral. The test is made by dip- ping strips of red and blue litmus paper in a glue solution, and noting the color change. (The solution left after the viscosity test may be used.) An acid glue turns blue litmus red, and a neutral glue will not change the color of either red or blue litmus. Alkaline glues will turn red litmus blue. A slightly acid glue is preferable to a neutral or alkaline glue, because it is not quite so favorable a medium for the growth of the organisms which cause the decay of glue. Strong alkalinity usually means an over-limed glue, which will almost surely cause trouble. To determine insoluble matter dissolve 30 grams of glue in one liter of hot water, and allow to stand for 12 hours in a warm place. Filter the hot solution through a weighed filter paper or good, crucible, wash well with hot water, dry and weigh. In hide glues the insoluble matter is rarely over 2 per cent. In bone glues it may be more. A little aniline color is added to the solution of glue in water (some of the solution remaining from the viscosity test may be used). The mixture is painted on unsized white paper and the appearance noted. Grease is visible in round, characteristic spots, and the relative amount present is indicated by comparison with other glues or the experience of the operator.* The water absorption test was proposed by Schat- termann in 1845. Glue does not dissolve in cold water, but has the property of absorbing several times its weight of water. Some glues will absorb eight to ten times their weight of water and still retain a rather firm consistency. Good glues will absorb at least six *See Jour. Soc. Chem. Ind., Feb. 28, 1906. GLUE TESTING 29 times their weight. A method used by the United States Bureau of Chemistry is as follows: Place 10 grams of the sample broken in small pieces in a beaker and cover with 200 c. c. of water at 15 C. Cover the 11 11 e j? n *. i -.LI SIGNIFICANCE beaker and place in a refrigerator for 24 hours, with OF THE TEST the temperature between 14 C. and 18 C. Then pour off the water and weigh the glue. This determination cannot often be made above 20 C. The firmer the jell the greater the glue strength (in general), and the more water that is absorbed the greater the covering capacity of the glue. If the glue becomes slimy, or if the solution shows evidence of putrefaction, poor quality is indicated. The melting point of the glue solution is of interest as it is a measure of how quickly or slowly the glue will set. It is sometimes used as a substitute for the MELTING viscosity test. The test is sometimes made as follows : POINT - Weigh 15 grams of the sample and soak 12 hours in a flask with 30 c. c. of water. Then immerse the flask in boiling water and shake well until the glue dissolves. While still liquid pour some of the solution into a test tube and close the end with a cork, and cool for one hour in water at 15 C. Now place in a water bath in an inclined position, with a thermometer, and gradu- ally raise the temperature. When the glue leaves its vertical position the temperature may be taken as the melting point. A simpler and more accurate method is in use at the Forest Products Laboratory. A drop of the liquid NEW glue solution is run into a glass U tube of small size. MELTIXG The tube is then cooled in water for 10 minutes at 15 PO INT TEST. C. It is then placed in a water bath and the tempera- ture raised gradually. The melting point is taken as the temperature at which the slug of glue moves down- ward in the U tube. For information in the literature on the melting point determination see R. Kissling (Chem. Zeitung, 1901, 25, 264 and Jour. Soc. Chem. Ind., 1901, 21, 509), also N. Chercheffsky (Chem. Zeitung, 1901, 25, 413, and Jour. Soc. Chem. Ind., 1901, 25, 731). CHAPTER VI. VISCOSITY THIS test is one of the most important of the tests made on glue, and is in universal use by glue manufacturers. (See Fels, Chemical Zeitung, 1898, 9, also Jour. Soc. Chem. Ind., 1890, p. 654.) Viscosity is a term used to describe the degree of TYPES O F fluidity of the glue solution. The thicker the solution VISCOSIMETERS. the higher its viscosity and the lower its fluidity or flowing power. Instruments for measuring viscosity (viscosimeters) are of various kinds. Those usually used for glue testing are of the orifice type, and depend in principle upon the time required for the passage of a known quantity of liquid through a standardized orifice, at a known temperature. Any viscosimeter of the orifice type may be used. Fels used a modified Engler (Jour. Soc. Chem. Ind., 1890, p. 654), with a 15 per cent, solution (15 grams of glue in 100 c. c. of solution). Rideal preferred a type described by Slotte and modified as described in the Journal Society Chemical Industry, 1891, page 615. A later modification is described by Scarpa (Gazetta Chemica Italiana, 1910). Some observers express vis- cosity in the number of seconds required for the glue solution to pass through the orifice of the apparatus. - 5 * dps S.S g go -> .-^-2^. r2 Description of v, 3 o < 9 * 2 > *J S 6 Samples || | M g.S ||S 1. Light yellow transparent thick ' plates 163 149 1.65 2. Brown transparent glue 14.0 125 1.36 3. Sherry yellow transparent glue 15.4 171 1.91 4. Light yellow plates 18.2 150 1.60 5. Muddy (truber glue) 15.2 199 2.21 32 MODERN GLUES AND GLUE TESTING A POPULAR RAPID TYPE OF VISCOSIMETER. Others prefer to express it as the ratio between the time required for the glue solution to pass through the orifice compared with water at the same temperature. Fels, with a 15 per cent, solution at 30 C., obtained the results shown in the table on page 31. Other workers, using different instruments, ob- tained different figures. The value obtained depends upon the form of the apparatus and the size of the orifice. For comparative purposes only, a home made de- vice may be used. One may be made from a volumetric pipette, fitted with a stop cock. The lower end is heated in a glass flame and carefully reduced in size until its inside diameter is of the desired size. One recommended by Jerome Alexander (Jour. Soc. Chem. Ind., 1906, p. 159) is made from a 45 c. c. pipette, and will pass 45 c. c. of water at 80 C. in 15 seconds. It has the follow- ing dimensions: Capacity, 45 c. c. of water at 80 degrees C. Internal diam. of effluent tube 6 mm. External diam. of effluent tube 9 mm. Length over all of effluent tube 7 cm. Smallest diam. of outlet (about) 1.5mm. Outside diam. of bulb 3 cm. Length of bulb 9.5 c. Length of upper tube 22 cm. This pipette is surrounded with a water bath, and the flow of solution is controlled with a pinch cock and rubber tube fitted over the top. Some glue factories, where a great many samples have to be tested every day, use a more rapid home made apparatus, with an orifice so large that the glue solution will pass through in 10 or 15 seconds. One can be made from a pipette as described, or from a glass tube contracted at one end. For several reasons such instruments are seldom very accurate. Better control of temperature and greater accuracy can be had with the Engler viscosimeter. This is more complicated and more expensive than the pipette or glass tube type, and is also slower to operate, but it VISCOSITY 33 GREASE RECORD Date. Index No.. Glue NOTE Grease is not of necessity a serious defect in Glue, except in certain specific uses. It does reduce foam and affects adhesiveness. Normal The white spots show the grease. O is Free of Grease. 5 and under is Commercially Free 6 to 20 " Normal 21 to 35 " Slight Excess 36 to 50 " Excess 51 and over " Very Greasy Examining Chemist The amount of grease in the glue is indicated by the light spots. This sample is "Normal." 34 MODERN GLUES AND GLUE TESTING GREASE RECORD Date. Index No. Glue NOTE Grease is not of necessity a serious defect in Glue, except in certain specific uses. It does reduce foam and affects adhesiveness. Very Greasy The white spots show the grease. is Free of Grease. 5 and under is Commercially Free 6 to 20 " Normal 21 to 35 " Slight Excess 36 to 50 Excess 51 and over " Very Greasy Examining Chemist The large number of white spots shown in this sample indicate "Very Greasy" glue. VISCOSITY 35 has the advantage, in addition to greater accuracy, of being an instrument which is in general use for testing many kinds of materials. The values obtained by its EXGLER use are readily understood by laboratory men and can VISCOSIMETER be readily checked. It can be purchased from supply is houses standardized and ready for use. The Engler RECOMMENDED. viscosimeter is in use at the Forest Products Labora- tory, and is required by the specifications for glue of the army and navy. It is recommended for standard- ized work on glues. The viscosity determination is made at the Forest Products Laboratory as follows : One part of glue by weight is dissolved in 5 parts of distilled water by weight. The sample is strained to remove insoluble matter, and the viscosity determined in an Engler viscosimeter within five minutes after the sample has been melted. The viscosity is expressed in terms of the number of seconds required for 200 c. c. of glue solution at a temperature of 60 C., to pass through the standard orifice of the viscosimeter, compared with distilled water at the same temperature. The precaution of straining the glue before testing should not be overlooked. Insoluble matter may clog the orifice and materially affect the result. The viscosity test is of great value in grading glues, SIGNIFICANCE and is one of the most important tests that is used. OF VISCOSITY In general, viscosity is a gauge of glue strength, high TEST. viscosity corresponding to high strength. It would lead to great error, however, if complete reliance were placed on the results of this test. It should only be considered in conjunction with other tests. Glues pro- duced from the same stock, under identical conditions, may be graded on the viscosity test. But glues under test may have been produced from different stocks by different methods. Hence considerable error may be found by relying on viscosity alone. Acid treated bone glues give viscosities very low in proportion to their jelly strength. Opaque and colored glues give higher viscosities than clear ones of corresponding strength. Glue stock incompletely washed, or over-limed gives a high viscosity. Some clarified glues have a low viscosity, both bone and hide. 36 MODERN GLUES AND GLUE TESTING Or if clarified with alum, the viscosity will be too high. Rabbit glues are liable to have viscosities that are too high to correspond with their jelly strength. The apparatus used may also lead to slight errors, as glues do not always grade the same when tested with different instruments. CHAPTER VII. JELLY STRENGTH ONE of the most significant and important of the tests commonly made on glue is an esti- mation of jelly strength. It was suggested by Lipowitz in 1861 and has been extensively adopted. It is made on a solution of the glue in water cooled to a jelly in a refrigerator, and consists in an estimation of the strength or firmness of the jelly. In spite of numerous attempts to develop apparatus for obtaining a measure of jelly strength in terms of some tangible numerical unit, the finger test is still favored by those most expert. The finger test is akin to tea or wine tasting in that it requires long experience and great skill to obtain good results. THE FINGER The finger test is made on a 25-gram sample soaked TEST FOR JELLY in 300 c. c. of water at room temperature. Melt and STRENGTH. stir the solution, and place in a refrigerator for at least 15 hours at a temperature between 5 and 10. degrees C. (40 to 50 degrees F.) Test either in the refrigerator or immediately after removal. The operator uses the third finger of the left hand and measures the resistance by pressing on the glue jelly. Any difference between different samples is noted, and the samples may be grouped in accordance with this resistance. In the Lipowitz test a small pointed plunger with a funnel at its upper end is inserted in the jelly. The funnel is loaded gradually with shot until the load THE LIPOWITZ is just sufficient to force the plunger entirely through TEST - the jelly from its top surface to the bottom of the cylinder. The weight of shot necessary to effect this gives the Lipowitz number. An apparatus invented by Edmund S. Smith is on the market which makes jelly tests without breaking the surface of the glue. It does not give good results on extremely high or low grades. It is rather com- plicated, and requires frequent cleaning and attention. It consists in principle of a thistle tube, over which is MODERN GLUES AND GLUE TESTING stretched a thin sheet of rubber. At the other end of the tube is a bulb for obtaining air pressure, and a sensitive pressure gauge or water manometer. The pressure tube is also filled with water. The observa- tion is made by forcing the rubber diaphragm into THE SMITH the glue jelly with air pressure from the bulb. The JELLY TESTER, measurement of jelly strength is made by noting the pressure on the gauge or manometer, and the amount that the diaphragm is forced into the glue is measured or controlled by a reading of the water level in the pressure tube. The jelly strength is measured on the gauge or manometer. The apparatus must be adjusted uniformly on the different samples to fee tested, and the distortion of the diaphragm must be the same in each test. The apparatus is covered by patent No. 911277. Jerome Alexander (Jour. Soc. Chem. Ind., 1906, 25, p. 160) describes a device "consisting of a brass cylin- drical vessel supported like a gas tank by four vertical rods, against which it slides with almost frictionless roller bearings. This brass cup is allowed to rest on a truncated cone of jelly of definite size, composition and temperature. Shot is gradually poured into the cup until a definite expression of the jelly is observed. Be- neath the cup are two vertical adjustable brass up- rights 3.5 c. m. high, connected with an electric bell circuit. When the cup reaches their level the bell rings. The weight of the brass cup, plus the weight of the shot, gives a figure which expresses the jelly strength." After thoroughly testing most of the above methods, as well as numerous other ones, an apparatus was adopted at the Forest Products Laboratory that is described in the appendix. This apparatus was modified from one in use in the glue laboratory of Armour & Co., Chicago. (See Appendix.) The jelly test, together with viscosity, are the most important of the tests made on glues, and all other tests must be considered in conjunction with them if the operator is to form a true conception of the grade of the glue sample. Both tests must always be made to obtain a fair comparison between an unknown JELLY STRENGTH 39 sample and one of Peter Cooper's standard. To say that a glue tests 1 Extra means that its jelly strength and its viscosity must be the same as a standard sample of Peter Cooper's 1 Extra. Obviously, the operator GLUE STANDARD must secure standards of known strength before he SAMPLE s ARE can rate his glues, as it is practically impossible to de- XEEDED - fine a method of test and an apparatus with sufficient exactness that the glue may be rated without the use of standards of comparison. Therefore it is of the utmost importance that the operator secure or have in his possession standards of known value before he can rate and value the unknown sample. Peter Cooper standards may be purchased from the Peter Cooper Glue Company. In making jelly strength tests it is well to re- member that sulphates in the glue increase the jelly strength (as well as viscosity), while chlorides and nitrates diminish it. CHAPTER VIII. STRENGTH OF THE GLUED JOINT. EVERY user of glue in wood work is interested in the strength of the glue. Hence numerous ef- forts have been made to devise tests that would measure the strength of the glue in the joint. The literature is full of descriptions of tests of one sort or another, and quite frequently statements are found JOINT to the effect that the results obtainable are variable or STRENGTH unreliable. Many thousands of tests have been made TESTS MAY BE at the Forest Products Laboratory, Madison, Wis., and DECEPTIVE. as a result of these, the author is forced to admit that most of them do not measure the strength of the glue, but rather are a measure of the quality of workman- ship or skill of the operator in making the joint. With the utmost skill and the best methods of workman- ship, it is possible to produce joints with grades 1*4 or higher that will always break the wood. Possibly the grade of 1% may be the dividing point. Dense maple, chosen because of its great shear strength, was used in these tests. Some information on grades below 1% may be obtained by strength tests. Usually speci- mens glued in the factories or by the average carpenter fail in the glued joint many hundreds of such have been sent in for testing. But the same glues can be made to give a joint so strong that wood failures result. The best joints made by carpenters and workmen have been produced with grades about Peter Cooper No. 1. Glues grading higher probably set too fast, and since the workman does not often produce a joint 100 per cent, perfect, those grading below that do not develop the full strength of the wood. The glue chemist should have a rather clear un- derstanding of the fundamentals of testing glue joints, or he may draw erroneous conclusions from his results. He is possibly more liable to be measuring his own ability to do "stunts" with the glue rather than measure the strength of the glue. In any case, with grades above 1%, watch yourself closely. The strength 42 MODERN GLUES AND GLUE TESTING THE SELECTION OF WOODS FOR GLUE TESTS.! I test has been very useful in obtaining data on the effect of various operations, such as time of pressure, etc., on the strength of the glue joint. It is also true that a good strong joint cannot be obtained with a glue that lacks adhesiveness. In order to develop as nearly as possible the full strength of the glue it is necessary to use wood of good gluing qualities and of high shearing properties. Not all species meet these requirements. The following table, based on tests on small clear specimens of material, gives a number of species which have an average unit value in shear parallel to the grain of over 2,400 pounds per square inch at 8 per cent, mois- ture, as well as a number of other common species with shearing strength below this value. In general the shearing strength of wood when the surface of failure is tangential is about 8 per cent, greater than when the surface of failure is radial. This SHEARING STRENGTH OF WOODS AT 8 PER CENT MOISTURE WITH SPECIFIC GRAVITY VALUES Specific gravity oven dry based on volume When When oven- Species green dry Ash, white (forest grown) .52 .60 Beech 54 .66 Birch, sweet 59 .70 Cherry, black. 47 .53 Dogwood (Flowering) 64 .80 Gum, red 44 .53 Hickory, big shellbark 62 Locust, black 66 .71 Locust, honey 60 .67 Maple, sugar 56 .66 Oak, Canyon live 70 .84 Oak, Commercial red 56 .67 Oak, Commercial white 59 .71 Persimmon :... .64 .78 Walnut, black 51 .56 Yew, western 60 .67 Shear parallel to grain surface of failure Tan- Ra- gen- Aver- dial* tialt age 2331 2021 2176 2256 2397 2326 2873 2811 2842 1780 2294 2037 2680 1734 1900 1817 2510 2536 2523 2516 3391 2954 2391 2514 2452 2602 3030 2816 2370 2628 2499 1906 2263 2084 2136 2466 2302 2185 " 2671 242S 1273 1552 1412 2326 2861 2594 * By radial surface of failure is meant a plane of failure per- pendicular to the growth rings. tBy tangential surface of failure is meant a plane of failure parallel or tangent to the growth rings. IIFrom paper by L. J. Markwardt, Forest Products Labora- tory. STRENGTH OF THE GLUED JOINT 43 44 MODERN GLUES AND GLUE TESTING SHEARING STRENGTH OF WOOD. VARIATION IN STRENGTH OF WOOD. indicates that higher values would be secured from most species by makir.g the surface of failures tangential, but in some species the reverse appears to be true. The radial shearing strength would be influenced to a con- siderable extent by any season checks which may exist in the material, and consequently any material contain- ing checks should be eliminated. The probable variation of the results of a single test from the average of the species is less for shear than for some of the other important mechanical prop- erties. This indicates that deviations from the average values given in the table would be smaller for shear than for the other properties. In general, in species having a shearing strength of 2,600 pounds per square inch about three-fourths of the pieces, without selection, would be expected to give unit shear values above 2,400 pounds. The proportion of individual pieces having a shear strength greater than 2,400 pounds would, of course, be larger for species whose average shearing strength is above 2,600 pounds per square inch. The shearing strength of wood, like the other mechanical properties, is closely related to the density or dry weight of the material. In general the lighter species, therefore, are inferior to the denser ones in shearing strength, and, likewise, within a given species the heavier pieces would normally exceed in strength those which are lacking in density. The selection of material on a density basis consequently presents a method by which the poorer specimens of most species may be eliminated. In species having an average shear- ing value of 2,800 pounds per square inch, about three- fourths of the individual pieces 5 per cent, below the corresponding average density would be expected to give unit shear values of 2,400 pounds or over, while about half the pieces at 10 per cent, below the average density equal or exceed the latter shearing stress. The moisture content of the wood when below the fiber saturation point* is another factor which influ- *The fiber saturation point is that point at which no water exists in the pores of the timber, but at which the cell walls are still saturated with moisture. The fiber saturation point varies with the species. The ordinary proportion of moisture, based on the dry weight of wood, at the fiber saturation point, is from 20 to 30 per cent. STRENGTH OF THE GLUED JOINT 45 VARIATION IN APPLICATION OF GLUE AND MANUFACTURE OF JOINT. ences the strength, the strength increasing with de- crease of moisture. In general, a moisture content EFFECT OF above this point does not affect the strength. The MOISTURE ON material for gluing should, therefore, probably be at STRENGTH. least as low at 13 per cent, moisture. While a number of species have very high shearing values, several other points must be taken into con- sideration in selecting material for glue tests, such as the property of taking glue, and availability. Sugar maple has been found to give very good results, is easy to procure, and when straight grained and free from defects is recommended as a shearing material for glue tests. Sweet birch would likewise be expected to prove satisfactory for this purpose. The question of the significance of joint strength tests made on grades better than 1% has already been raised. It has been found that joints made at just the instant the glue begins to chill are very strong. It is almost impossible to always have the glue film of the same thickness in successive test pieces, and the thickness of the film very markedly affects the joint. Above all avoid a film too thin (a starved joint). A starved joint can be obtained by using too much pres- sure. It will be obvious that before the operator can feel that the results of his strength tests are reliable REQUIREMENTS he must know all the essentials of producing a perfect FOR OBTAINING joint, and be perfectly certain that he has succeeded MAXIMUM in doing so. He is advised to do considerable experi- STRENGTH. menting with joints made under different conditions before relying upon his results. This more properly resolves itself into a discussion of methods of testing. It is of course possible to ob- tain some information from almost any sort of strength test that will rupture the glued joint. Thus the workman may try to split the joint with a chisel. If it follows the glue, either he has a poor joint or the IMPROPER glue is weak. Such tests are relatively of very little APPLICATION v value, as even low grade glues may not split along the OF THE LOAD. joint if a soft or weak wood is used. With very hard, strong woods it is possible to obtain an idea of the strength, but not in terms that can be readily ex- pressed. Such tests should be carried out on strong 46 MODERN GLUES AND GLUE TESTING APPLY LOAD UNIFORMLY. THE SPAN DA U TEST. woods, as maple or birch. Even oak is hardly strong enough in shear to test ordinary grades of glue. When the attempt is made to measure the load necessary to rupture either the wood or the glued joint, the results are liable to be so variable as to mean nothing unless properly applied. Any test that does not apply the load uniformly over the test piece is to be regarded as of doubtful value. Such tests usually can be resolved into applying the load on the joint in shear, in tension, in cleavage or by twisting. Only the first two should be considered by the glue tester. In the latter two the load is concentrated on small areas, which give way and allow the load to then be con- centrated on adjacent areas. The piece can never show its maximum strength, as it can when the load is applied uniformly. This is a test proposed by Karmarsch and adopted by the Artillerie Werkstatte, Spandau. It has been much used in America. Cement testing machines are often used, or sometimes a system of levers is devised that works well. Samuel Rideal (Glue and Glue Test- ing) reports great difficulty in obtaining check results, due to non-uniformity in the wood, and in the surface of the wood at the glued joint ; time of heating the glue and temperature of gluing, thickness of glue, pressure used, uneven application of pressure, presence of lumps; variation in the moisture in the air, tempera- ture while setting, duration of time between gluing and testing ; temperature while testing ; uneven application of load. Truly a formidable list of causes for varia- tion, and obviously requiring skill and knowledge of the subject to secure consistent results. The Spandau test, as officially adopted in Germany, consists in gluing together two blocks of wood with a plain butt joint with the grain end to end. The blocks are 40 mm. square in cross section, and 210 mm. long. The glue stock is prepared by dissolving 250 grams of glue in 500 c. c. of water. The blocks having been glued together, one is fixed horizontally to a table in such a manner that the joint between the two blocks overhangs beyond the edge of the table. A scale pan is attached to the block at a given distance beyond the STRENGTH OF THE GLUED JOINT 47 edge of the table and weights are added until the 'joint fractures. This test cannot be recommended very highly, be- cause it places the top of the joint at a maximum strain, while the bottom is in compression. A uni- formly applied load is much superior. A test adopted by the British Royal Aircraft factory in their specification of Nov., 1916, uses a double wedge shaped block (See Fig. 2). It is made BRITISH BLOCK by gluing together two pieces of American walnut. AIRCRAFT TEST. Glue Joint FIG. 2 The glue solution is prepared according to the glue manufacturer's instructions. The test joint has dimensions 3 in. by 1 in., and is required to support a static load of 187 pounds per square inch in direct tension. The test is made at 122 F. at normal humidity, in a fully saturated atmosphere, and sub- merged in water. The load must be supported for various lengths of time in these tests, depending upon the grade of glue desired. The Aeronautical Inspection Directorate (Eng- land) tests a sample of the form shown in Fig. 3. American walnut is used and the glued surfaces Gluo Joint FIG. 3 48 MODERN GLUES AND GLUE TESTING slightly tooth-planed. The specimen is supported at the ends in a testing machine and the load applied in ANOTHER the center. Precautions are specified for the tempera- BRITISH TEST, tures, pressures used in gluing, preparation and appli- cation of the glue, etc., that insure reasonably uniform results. The fundamental objection is that the load is not uniformly applied to the glued joint. Fairly con- sistent results may be obtained, however. Of the numerous methods experimented with at the Forest Products Laboratory, Madison, Wis., the ten- sion test and the shear test were the only ones that gave reasonably accurate results. The tension test was discarded because it does not represent the most common practice of gluing wood, and is furthermore inconvenient and slow. It can, in one form or another, however, be satisfactorily used to determine glue strength. Glue Joints FIG. 4 AVOID THIS METHOD. A test specimen as shown in Fig. 4 has been widely used*, but was discarded at the laboratory. This specimen is made of three pieces glued in the form shown, with 4 square inches in each joint. The speci- men is placed in the testing machine and tested in com- pression. This test appeals to people because it does not require a tool or special device to test in a testing *See Jerome Alexander (Jour. Soc. Chem. Industry, 1906, 25, 160). STRENGTH OF THE GLUED JOINT 49 machine. It is not recommended, however. It is men- tioned here because of its rather widespread use, and the temptation to use it in the absence of complete equipment. The objection lies in the fact that when the load is applied, the two outer pieces spread apart at the bottom, giving a failure in cleavage instead of u. s. ARMY in shear. The test as finally adopted at the Forest AND NAVY TEST. Products Laboratory uses a specimen as in Fig. 5. The FIG. 5 wood is prepared conveniently as in Fig. 6, which is self explanatory. It is necessary to use a shear tool. A drawing of this is shown in Fig. 7. Fig. 8 shows a specimen under test in the testing machine. A complete description of the Forest Products Laboratory method is given in the appendix. A modi- fication of this method has been used to some extent by sawing the specimen as shown in Fig. 9. This specimen is then tested in compression with- out the use of a shearing tool. The author cannot vouch for this method, as he has never used it. A rather common method of glue testing is to cut a series of boards as shown in Fig. 10. These boards A SIMPLE BUT are glued together as the vertical straight lines in- INACCURATE dicate. After the glue has set, a wedge is driven in METHOD. at the places indicated by the arrows. The claim is made that a good grade of glue should always hold the pieces together so firmly that the glue joint does not give way, but that the wood itself will split or be 50 MODERN GLUES AND GLUE TESTING Ghed Joint Spec\mens l -~Firs't Step METHOD OF PREPARING SPECIMENS FOB. GLUE STRENGTH TESTS FIG. 6 STRENGTH OF THE GLUED JOINT 51 ruptured. This method is guesswork and yields no results for the reason that no matter how much the strength of the wood may vary, the test does not in- dicate this variation. Furthermore, the result cannot be expressed in figures. Another common method is to glue up two pieces from 10 to 12 inches in length and of suitable width to fit into a bench vise. After the glue has dried, the glued boards are placed into the vise so that the 52 MODERN GLUES AND GLUE TESTING entire joint stands out from three to four inches. The workman strikes the joint with a hammer, and it is claimed that if the glue joint is weaker than the wood the joint will break; if not, the wood will split. The results obtained in this test are absolutely worthless. FIG. 8 Figure 11 shows a simple scheme that will likely appeal to some. The heavy straight vertical line represents a wall or post. A represents a heavy hinge being fastened to the wall and beam B. C represents a block, the end being rounded so as to fit part way into the "V" cut opening of the glued test piece E. D represents the platform of a so-called platform scale. The beam STRENGTH OF THE GLUED JOINT 53 is 10 feet long by 4 inches by 2 inches. The test piece is usually 10 inches by 3 inches by % mcn each, two pieces glued together and the top cut out either "V" or "U" shaped. C is placed in the opening ; this block, as the illustration will indicate, being a little larger than the slot into which it is fitted. The weight on the end of the beam required to break the pieces is read and recorded. N0 TEST FIG. 9 A simply made lap joint test is worthy of men- tion. Carefully selected pieces of a hard wood are used for this test. The moisture content is determined. THIS is A The pieces are jointed and sized, so that they will be FAIRLY GOOD exactly 8 inches long by 1 inch by 1 inch. The thick- ness and width should be determined with a micro- meter. The pieces are then lap-glued as per illustration, HOME-MADE DEVICE. FIG. 10 54 MODERN GLUES AND GLUE TESTING and we now have a glued surface of exactly one square inch. In studying Fig. 12 the reader will ob- serve blocks B. They are glued into the corners of the testing machine, one being 2 inches, the other 1 inch thick. Par. represents a partition or wall through which the plunger P passes. P is a stick of wood one inch square of convenient length to which T, a support for the weights, W, is fastened. c V D FIG. 11 The glued pieces are stored in a dry room for from three to four weeks. The test strips are next placed in the testing machine upon blocks B. Weights are added on T until the lap breaks, and the weights to accomplish this are recorded. The objection to this method is that the load is not applied uniformly over the glued joint. Test pieces. 6X7X7 6X1X1 FIG. 12 STRENGTH OF THE GLUED JOINT 55 The difficulty of obtaining satisfactory results from strength tests on glued wood joints has inevit- ably led investigators to try other schemes for test- MISCELLANEOUS ing strength. The .experience of the Forest Pro- STRENGTH ducts Laboratory has led them to feel that schemes TESTS - for testing the strength of the film, or of some por- ous material such as plaster or earth cemented to- gether with the glue may have merit. A method of glue testing suggested by Karmarsh and modified by Weidenbusch, 1859, consists in break- ing small rocks of plaster of paris cast in molds of A PLASTER uniform size and saturated with glue solutions of R D TEST. known strength and dried thoroughly. They are then horizontally supported at their ends and loaded in the center, the weight required to break the rod being the so-called Karmarsh, or Weidenbusch, figure for the cor- responding glue solution. Setterberg (Schwed, techmks Tideskrift, 1898, XXVIII, 52) soaks strips of paper in the glue solu- tion. The excess of glue is removed with filter paper, THESE TESTS the strips allowed to dry, and tested in a paper testing WARRANT machine. CONSIDERATION. Gill (Jour. Ind. and Eng. Chem., Feb., 1915, p. 103) tried the tension test, gluing blocks together endwise. He also tried porcelain, glass, and tiling. He could not secure uniform results, and then dipped filter paper in the glue solution, dried and tested. His conclusions are as follows : "The method of testing glue by measuring the strength which it imparts to bib- ulous paper is dependable and gives fairly concordant results." CHAPTER IX. PLYWOOD STRENGTH TEST.* A HIGHLY satisfactory method of testing glues in veneer panels or plywood was developed at the Forest Products Laboratory. It was adapted from the English A. I. D. method. An experienced TEST SUIT ABLE operator can make from 500 to 1,000 tests a day. A FOR VENEER large number of tests on each glue may thus be made, WORK. reducing the variables due to a small number of tests. The specimen for this test is prepared as shown in Fig. 13 and the test is made by placing the speci- i j FIG. 13 men in the grips of a testing machine and exerting a pull upon it. This causes the joint to fail either in the glue or the wood, or both. The English requirement is that the glue joint in the plywood must show a strength of at least 150 pounds per square inch in this test to be acceptable. On the basis of several thousand tests on plywood secured from various American manu- facturers it appeared that a minimum average of 150 pounds per square inch may also be safely required for American plywood. *From paper prepared by Teesdale and Colgan, Forest Prod- ucts Laboratory. 58 MODERN GLUES AND GLUE TESTING Fig. 14 shows the style of grips first used, as recom- mended by the English reports, to do away with the free pivot motion allowed by these grips a special jaw was designed as shown in Fig. 15. These jaws were in- FIG. 14 serted in the Riehle cement tester as shown in Fig. 16. The upper jaw is hung on a knife edge, since it is a part of the leverage system of the balance. The lower jaw is rigidly fastened except for the vertical motion in oeprating the machine. A guide attached to it counter- acts the tendency of the upper jaw to swing in the di- rection of opening of the upper saw cut. When adjusting a specimen into these jaws the only additional precaution necessary is to make sure that PLYWOOD STRENGTH TEST 59 it is centered in order to get a straight pull. This is done by adjustable thumb screws which control the position of the grips. The bucket attached to the lower arm at the left contains small lead shot, which are released by a valve- like mechanism and flow into the pan on the spring scale placed below. The load is applied to the specimen now TEST is in the holder by means of the wheel at the right. As MADE. FIG. 15 the load is applied, the shot are released from the buck- et and flow into the pan on the scale, which indicates the actual load applied. When the specimen breaks the flow of shot is automatically stopped. The difference between the strength values shown in the shear test on blocks and the English test on plywood is due to several reasons. In the shear blocks, 60 MODERN GLUES AND GLUE TESTING the grain of the two pieces glued together runs in the same direction, while in plywood the grain of the plies- WHY PLYWOOD runs m opposite directions. Changes in moisture con- STRENOTH tent due to the drying of the glue in the joint will, TESTS GIVE therefore cause stresses in the joint in the plywood to LOW VALUES. a very much greater extent than the shear blocks, be- cause the shrinkage of wood is much greater across the grain than along the grain. Also in making joints FIG. 16 PLYWOOD STRENGTH TEST 61 in thick material greater care is possible in the prep- aration of the surface and the application of the glue than in plywood. The continued flexing of plywood in handling also may have some weakening effect on the glue. The panels to be tested are cut into specimens one inch by three and one-fourth inches ; the test area being restricted to one square inch by notches cut DETAILED through one face and the core, on opposite sides of the DESORIPTION panel, one and one-eighth inches from each end. OF PLYWOOD A panel should preferably be three-ply and should TESTS. not have a core which exceeds one-eighth inch. Thin- ner cores are preferable. When thick panels are test- ed, it is sometimes necessary to plane them down to a thickness suitable for the machine before testing them. Panels with 1/64-in. plies are too thin to test, because it is practically impossible to make them into shear specimens without spoiling them. This test may be used to test the quality of glue or of workmanship in veneer panels. It may also be used to test the water resistance of glups by placing the test specimens in water or under humid conditions before being tested. 63 CHAPTER X. SPECIFICATIONS. readers inexperienced in glue testing may have gained the impression that the methods of -*- test are unreliable and of little value. This is by no means the case. It is true that testing methods are arbitrary, and that they cannot in general be expressed in terms of numerical values with sufficient exactness to write a specification. It was THE ARMY AND for this reason that in the work of the Forest Products NAVY GLUE Laboratory, all thought of attempting to prepare a SPECIFICATIONS. specification without the use of a standard sample was abandoned. The specification as evolved makes use of a standard sample which was selected as being satis- factory for the purpose, and of a grade not difficult to obtain. The specification then requires the manu- facturer to furnish glue at least equal to the standard sample in jelly strength, viscosity, grease, foam and odor. After two years of use, covering purchases of over a million pounds of glue for both the army and the navy, it can be said that the specification was very satisfactory, both to the manufacturer, the consumer and the specification department. Hence it can be recommended unqualifiedly to any purchaser of glue in quantities sufficient to warrant the expense of making tests. It would only be necessary for the buy- er to determine upon a standard sample of the quality he desires, and set aside a quantity, say 50 or 100 Ibs., to be used as a standard sample. The specification as given would apply in all respects except "adhesive- ness," where the required strength values would change with the grade of the standard sample. In these speci- fications the standard is about the equivalent of Peter Cooper's grade 1. 1. This specification covers the requirements of the Bureau of Aircraft Production for all hide glue used in the construction of propellers and for splices of airplane structural members. 64 MODERN GLUES. AND GLUE TESTING SPECIFICATIONS FOR AIRPLANE USE- STRENGTH TEST, U. 8. ARMY. MODE OF PROCEDURE. 2. The glue must be a high grade hide glue, sweet and free from any deleterious substances. 3. The glue shall be tested by comparison with a standard sample for jelly strength, viscosity, grease, foam and odor. The standard sample may be obtained from the Director, Forest Products Laboratory, Madi- son, Wis. 4. The following tests shall be made by a Bu- reau of Aircraft Production representative before cer- tifying or accepting any hide glue for use in aircraft construction. 5. The test for adhesiveness shall be made on 4 test specimens of the form and dimensions shown in Fig. 5, page 49. The test specimens shall be made of maple having a shearing strength of at least 2,400 pounds per square inch. This will require wood hav- ing a dry weight of about 50 pounds or more per cubic foot, and a moisture content of from 8 to 12 per- cent. 6. The glue shall be mixed with water in four different proportions by weight, and test specimens shall be prepared using the glue at each of these four dilutions. Unless otherwise specified, the proportions used shall be as follows: Water 1 Glue ... 1 n. III. IV. 2-% The glue shall be added to the water at room tem- perature, stirred thoroughly, and allowed to stand for at least two hours. It shall then be melted in a water bath, at 140 deg. Fahr. (60 deg. C.) and applied to the wood surfaces which are to be placed in contact. These surfaces shall fit perfectly together, and the wood shall be at room temperature. After gluing, the test blocks shall be held under a moderate and uniform pressure for 15 to 24 hours. At the end of this time they shall be released from pressure without subjecting them to shock, and allowed to stand for 6 days addi- tional. The test specimens shall be finished so that when they are ready for testing they shall have a glued joint two inches square, and conform to Fig. 5. The specimens shall be tested to destruction in a test- SPECIFICATIONS 65 ing machine approved by the Inspection Department. No test specimen shall fail under a load of less than 2,200 pounds per square inch, and the average shearing strength shall be at least 2,400 pounds per square inch. Specimens which fail under a load of less than 2,400 pounds per square inch will, if the failure occurs en- tirely in the wood, be excluded in calculating the aver- age shearing strength and the permissible minimum. The glue mixed with water in at least one of the four proportions as above shall comply with this strength requirement. The dilution at which the greatest strength is indicated will be recommended for use. 7. The jelly strength shall be determined upon JELLY a mixture containing 12 parts of water to 1 part of STRENGTH. glue. The glue shall be soaked, melted and poured immediately into a vessel of standard size and shape. It shall then be allowed to stand for at least 15 hours in a refrigerator at a temperature of from 40 to 50 deg. Fahr. (5 to 10 deg. C.). The relative strengths of the standard sample and the glue under test will be determined in the refrigerator, or immediately after removal therefrom, by pressure with the fingers or with some suitable apparatus approved by the Inspec- tion Department. 8. The viscosity shall be determined in an Eng- VISCOSITY. ler Viscosimeter upon a sample containing 1 weight of glue to 5 weights of water. The sample shall be strained and the viscosity shall be determined within 5 minutes after having been melted. The viscosity shall be expressed in terms of the number of seconds re- quired for 200 cubic centimeters of the glue solution, at a temperature of 60 deg. C., to pass through the stan- dard orifice of the viscosimeter. 9. The relative amount of grease present shall be GREASE. determined by mixing a dye with some of the glue remaining from the viscosity test, painting the mixture on unsized white paper, and observing the appearance. 10. The test for foam shall be made on the sample FOAM. used in the viscosimeter. The sample, after heating to 140 deg. Fahr. (60 deg. C.), shall be beaten for one minute with a power egg beater, or similar instrument, 66 MODERN GLUES AND GLUE TESTING INSPECTION. PRELIMINARY SAMPLE. and allowed to stand one minute or until the foam can be measured. 11. The odor of the glue, when in hot solution, must be sweet and must remain sweet for 48 hours; that is, free from any suggestion of deteriorating ani- mal matter. 12. The inspector shall have free access to all parts of the plant where this glue is being manufac- tured, and shall be afforded every facility to satisfy himself that the glue is in accordance with this speci- fication. 13. The tests shall be made on a sample from each lot of glue. The manufacturer of hide glue, when he has accumulated not less than 30,000 pounds which he considers to be in compliance with the specification, will make up a sample which shall be representative of the whole 30,000 pounds, grind it, if it is not already in the ground condition, and send at least a 2-pound sample of it to the Senior Inspector, Bureau of Air- craft Production, Forest Products Laboratory, Madi- son, Wis., or to a laboratory designated by the Inspec- tion Department, Bureau of Aircraft Production. It must be plainly marked "Preliminary Sample," and it must be accompanied by a written statement as to the amount of the glue represented by the same and in- structions concerning the method of using this glue which the manufacturer ordinarily furnishes the user. He shall notify the Raw Materials Department and the Inspection Department at Washington, D. C., when the sample is forwarded. 14. This sample will be tested by Bureau of Air- craft Production inspectors, and the results of these tests will be sent to the manufacturer as soon as pos- sible. 15. If the preliminary sample passes all tests, the manufacturer may proceed to mix thoroughly all the glue represented by the sample. He will advise the inspectors at the laboratory on what date it will be ready for final mixing, inspection and barreling. As near that date as possible, an inspector will visit the glue factory. In his presence, the glue will be given SPECIFICATIONS 67 such final mixing as he deems necessary. It will also be packed in tight drums or barrels in his presence; and, at the same time, he will take a sample which will be known as the official sample. The inspector will METHOD OF forward this sample to the Forest Products Labora- SEALINO - tory, or to a laboratory designated by the Inspection Department, for analysis. The results of this analysis will determine whether or not the hide glue can be certified. After the glue has been placed in barrels, the inspector will witness the "heading" of the filled barrels, and will seal both ends of every inspected bar- rel with serially numbered labels provided for the pur- pose. Each barrel shall also be marked with the name of the glue. Note The submitting of the preliminary sample is not required and may be omitted if so desired by the manufacturer. 16. The manufacturer will then put the inspected barrels in a place which is dry, sheltered and suitable for storage. Glue which is otherwise satisfactory, will be rejected if proper storage facilities are not pro- vided for it. 17. If the official sample proves to be in compli- ance with the specification, the manufacturer will be notified that the lot of glue covered by the official sample has been certified. Certified hide glue is the only hide glue which aircraft manufacturers will be permitted to use. Hide glue which does not comply in every respect with this specification will not be certified, and its use will not be permitted on govern- ment aircraft contracts. If an inspected glue fails to be certified, the manufacturer will be required to remove the inspection labels. 18. The glue manufacturer must report to the Raw Materials Department, Bureau of Aircraft Produc- tion, and to the Senior Inspector, Forest Products Lab- oratory, Madison, Wis., every sale of certified hide glue. The reports must be in duplicate and they should include the amount of glue, the number of the label of every barrel shipped, the name and address of the consignee, and the date of shipment (or sale). 68 MODERN GLUES AND GLUE TESTING SPECIFICATIONS FOR HANDLING HIDE GLUE. GLUE MUST BE SOAKED AT LEAST TWO HOURS. NO GLUE HEATED LONGER THAN 8 HOURS CAN BE USED. 19. No glue which has been rejected shall be of- fered to any department of the Bureau of Aircraft Production or to any aircraft contractor to the gov- ernment without a full statement of the cause of re- jection. 1. This specification is drawn to cover the re- quirements of the Bureau of Aircraft Production for the handling and testing of hide glue at airplane and propeller factories. 2. All the animal glue used in the construction of propellers and for splices of airplane structural members shall be hide glue certified in accordance with Specification No. 14,000-B. 3. Soaking. The glue and pure cold water must be weighed out separately, and according to the pro- portions recommended for the particular glue by the Senior Inspector, Bureau of Aircraft Production, Forest Products Laboratory: They should then be mixed, thoroughly stirred, and allowed to stand in a cold place in a covered vessel until the glue is thoroughly soaked and softened. The mixture must stand at least two hours. 4. Melting. After the glue has been sufficiently soaked, the water-glue mixture shall be melted on a water bath or in a carefully regulated electric heater. The glue solution must never be permitted to rise to a temperature exceeding 150 deg. Fahr. About 140 deg. Fahr. provides an excellent working tempera- ture. 5. Heating. Glue shall not be heated for a greater length of time than is absolutely necessary. Glue which has been heated for 8 hours or longer must not be used. All the glue which has been heated at any time on any day shall be rejected at the close of that day and must not be used on any succeeding day. In order to prevent the loss of moisture, the glue pot shall be kept covered when not in actual and continuous use. Any skin or scum which forms on the surface of the glue shall be removed. 6. Application. The glue shall be applied to the wood in a room which is free from draughts and as SPECIFICATIONS 69 warm and humid as healthful working conditions al- low. 7. Wood. The wood shall be uniformly dry and at least as warm as the air in the glue room. High temperatures and prolonged heating of the wood should be avoided in order to prevent distorting the surface. The wood surfaces shall "fit" perfectly and they shall be clean. 8. Spreading. The glue shall be applied to both APPLY GLUE surfaces of the joint, and shall be spread freely and as TO BOTH rapidly as is consistent with good workmanship. SURFACES. 9. Pressing. The clamp pressure or other pres- sure shall be applied quickly in order to prevent the glue from jellying or setting. A sufficient number of clamps should be used to insure that the wood is in close contact at all points, and that the pressure is evenly distributed. 10. Sanitation. Only enough glue shall be mixed at any one time for one day's work. The glue pots, brushes, etc., shall be cleaned out each night with boil- ing water and all the glue left over after the day's work shall be discarded. The brushes will remain sweet if left over night in a solution of carbolic acid. 11. A glue test specimen shall be made of 1-inch TEST boards of sufficient size to furnish ten test specimens SPECIMEN. conforming to dimensions specified in Fig. 5, page 49. The boards shall be representative of the wood on which the glue is to be used. The specimen shall be made up under the average conditions prevailing in the glue room. The gluing shall represent actual practice and no special precautions other than those ordinarily taken shall be employed in preparing uie glue or wood. The gluing shall be performed by the employes of the airplane factory accustomed to this kind of work. TESTS MUST No protective coating of any kind shall be applied to BE MADE. the wood surfaces or to the finished specimen. The specimen shall be held in the clamps for 15 to 24 hours. After being removed from the clamps it shall stand for 6 additional days in a warm, dry place. The speci- men shall be cut into ten shear blocks which conform to the dimensions shown in Fig. 5, page 49. 70 MODERN GLUES AND GLUE TESTING INSPECTION*. 12. The following test shall be made to deter- mine the strength of the glued joint. Ten of the shear blocks shall be tested in a shearing machine immediately after sawing, and the strength of the glue in shear shall not be less than that of the wood. 13. The required strength must be obtained from 80 per cent, of the specimens tested. 14. Test blocks may be sent to the Senior In- spector, Bureau of Aircraft Production, Forest Pro- ducts Laboratory, Madison, Wisconsin, for this test. When blocks are forwarded for this test, they should be plainly and clearly marked and should be accom- panied by Bureau of Aircraft Production I. R. Form No. 68 (Request for Glue Tests). 15. The inspector of the Bureau of Aircraft Pro- duction shall have free access to all parts of the plant of the manufacturer where this work is being carried on, and shall be afforded every reasonable facility to satisfy himself that the work is in accordance with this specification. Tests shall be made under the super- vision of a representative of the Bureau of Aircraft Production. CHAPTER XI. RESULTS OF TESTS ON MISCELLANEOUS GLUES. TESTS in accordance with the methods outlined in the foregoing specifications on about 30 samples of animal glues obtained through miscellaneous sources were made. The results of these tests are of T considerable interest, both as a guide to the operator J^HREE and to the prospective purchaser of glues. The results L ^ BORATORIES are given in Tables 1 to 9. Some of these samples were sent by Laboratory F to two glue manufacturers, termed Lab. A and Lab. N, where the tests were made by their own methods. The comparisons obtained are very interesting. Table 1 gives a description of the samples tested. The results of the viscosity tests are given in Table 2. Since a different type of viscosimeter, and probably a different volume of glue solution was used by each VISCOSITY of the three laboratories, the results cannot be directly TSSTS. compared. This emphasizes the need for a standard apparatus and method of determining viscosities. In Table 3 the glues are arranged in order of their relative jelly strength. This arrangement shows n general agreement between the three laboratories as JELLY to which are the strong glues and which the weak. From the results of the various comparative tests described above, it might be presumed that these tests are of little value, and might as well be discarded. This is not the case, however, for while it is true that the results from different laboratories cannot be directly compared, because the methods of test are different and THE RESULTS because of the personal equations, at any one labora- CANNOT BE tory the value of a glue can be pretty closely approxi- COMPARED mated by the use of these tests, because they are made DIRECTLY. in the same way each time. The results above quoted, however, show, very emphatically, the need for a stan- dard system of testing to be followed by all glue lab- oratories. 72 MODERN GLUES AND GLUE TESTING The reaction of the various glues to litmus is shown in Table 4. It seems strange that there should be such a disagreement among the three laboratories as to whether the glues were acid, alkaline or neutral. In most cases, of course, the reaction was very slight in either direction, and the difference must be due either TABLE 1. DATA ON GLUE SAMPLES. Kind (Information Price* Sample from manufac- quoted No. turer.) per Ib. 1.... ....Animal. 2 Animal. J 3 Blend of fish and 46c animal. 1 4 Animal. 60c 5 F i r s t run pure 51c hide glue. 7 8 Vegetable glue. 9 V e r y high-grade glue. 10 Hide glue. 11..... Hide glue. 12 Hide glue. 13.... 14 15.... Thin cut clear 60c flake glue. 16 Extra clear flake 45c 17.... glue. Medium cut clear 50c flake glue. 18 Highest testing. 19.... 65c 20.... Pure rabbit skin glue. 21.... Exceptional water 55c taking qualities. Less Freight 22.... 23 24.... 25.... 26.... 27 ....Pure hide elue. 50c Remarks. Recommended by the manufacturer for hard- wood. Recommended for soft- woods. A special fish blend joint glue. Prepared paste. Probably a casein product. From lab. stock. Prob- ably foreign glue. Contains a large amount of mineral matter. 28 High-test glue. "June, 1917. RESULTS OF TESTS ON MISCELLANEOUS GLUES 73 to the difference in judgment of the men who made the tests, or to a difference in litmus paper. Laboratories A and N did not report upon this KEEPING test. From Table 5 it is apparent that practically all QUALITIES. the glues would have passed a test requiring that they stand 48 hours without showing signs of deterior- ation. Table 6 shows typical results selected at random from glues tested by W. L. Jones, B. A. P. inspector TY PICAL stationed at the Forest Products Laboratory, the RESULTS methods being those described in the appendix. The OBTAINED BY table is arranged in order of increasing viscosities, USE OP ARMY and is given here as it may be useful to the operator METHODS. attempting to use the proposed methods. TABLE 2 RESULTS OF VISCOSITY TESTS. Glue No. 1 Lab.F Seconds .. 173.9 Viscosity Lab. A Seconds 52.0 50.0 51.0 50.0 53.0 58.8 50.6 55.5 54.0 44.0 52.0 55.5 54.0 55.0 51.0 5l'.5 56.5 50.5 48.0 49.6 53.4 42.0 52.0 58.6 Ratio to Viscosity of Water Lab.N Lab.F* Lab. Af Lab. NJ Seconds 23.00 3.30 1.24 1.53 21.00 2.69 1.19 1.40 20.75 2.82 1.21 1.38 20.75 2.65 1.19 1.38 20.5 4.18 1.26 1.37 25.00 5.48 1.40 1.67 22.5 3.04 1.20 1.50 24.25 4.39 1.32 1.62 23.00 3.76 1.29 1.53 18.25 1.62 1.05 1.22 24.00 3.11 1.24 1.60 25.00 4.70 1.32 1.67 23.00 3.43 1.29 1.53 24.00 4.03 1.31 1.60 21.5 1.21 1.43 27.5 4.98 1.83 22.00 2.56 1.23 1.47 26.25 4.14 1.34 1.75 22.25 2.73 1.20 1.48 20.75 2.34 1.14 1.38 21.25 2.56 1.18 1.42 25.00 3.62 1.27 1.67 15.75 1.40 1.00 1.05 23.25 1.24 1.55 27.00 4.90 1.39 1.80 2 3 141.6 148 4 4 5 139.2 219.7 9 288.5 10 11 160.0 231.0 12 13 197.5 850 14 15 16 163.8 247.2 180.3 17 212.0 18 19 20 21 22 23 ... 261.8 134.8 217.6 143.6 123.4 24 25 134.8 190.1 26 27..... 28 73.5 ".'. 257.7 *Compared with the viscosity of water at 20 C., which is 52.6 seconds in this instrument. (Engler.) fConipared with the viscosity of water at 60 C., which is about 42 seconds in this instrument. ^Compared with the viscosity of water at 20 C., which is 15 seconds in this instrument. 74 MODERN GLUES AND GLUE TESTING No. Lab. A' 1 69 2 64 3 61 TABLE 3 RESULTS OF JELL TESTS 4 5 9 10 11 12 65 67 73 67 71 67 13 Too low 14 15 16 17 18 19 20 21 22 23 24 25 26 Too 27 70 28 72 Lab. N* 140 120 90 110 66 166 136 152 142 50 86 164 132 146 148 144 142 134 118 136 76 138 40 154 Lab. Ff 4 5 4 3 1 3 1 NOTE In Laboratory! tests, the glues were classified into groups according to their strength by finger test method as follows, group 1 being the strongest: Group 1 Nos. 9, 11, 28. Group 2 Nos. 23, 15, 19, 18, 17, 21. Group 3 Nos. 15, 5, 12, 10, 1, 27, 20. Group 4 Nos. 14, 2, 25, 24, 4, 22. Group 5 No. 3. Group 6 No. 13. Group 7 No. 26. 156 "These values represent numerical figures obtained with the instruments in use at these laboratories. tBy finger test method. TABLE 4- No. Lab. F 1 Slight acid 2 Slight acid 3 Very slight 4 Slight acid 5 Very slight 9 Slight acid 10 Slight acid 11 Acid 12 Neutral 13 Slight acid 14 Neutral 15 Neutral 16 Neutral 17 Neutral 18 19 Neutral 20 Acid 21 Neutral 22 Neutral 23 Acid 24 Neutral 25 Neutral 26 Neutral 27 28 Neutral acid acid REACTION TO Lab. Alkaline Alkaline Alkaline Alkaline Alkaline Acid Alkaline Acid Alkaline Acid Alkaline Alkaline Alkaline Alkaline Alkaline Acid Alkaline Alkaline Acid Alkaline Alkaline Alkaline Acid Alkaline LITMUS. A Lab. N Very slight acid Very slight acid Very slight acid Neutral Very slight acid Very slight acid Very slight acid Very slight acid Neutral Fairly much acid Neutral Neutral Neutral Neutral Very slight acid Neutral Fairly much acid Neutral Very slight acid Slight acid Neutral Neutral Neutral Slight acid Neutral RESULTS OF TESTS ON MISCELLANEOUS GLUES 75 A very interesting series of results is published by Linder & Frost (Proc. Am. Soc. Test. Mat., 1914, Part II, page 509). Data given on moisture, vis- cosity, cost, and breaking strength of 25 samples of glue. No. 1.... 2.... 3.... 4.... 5.... TABLE 5 KEEPING QUALITIES No. 10 11 12 13 14 15 16 Lab. F Hours* 142 52 142 142 142 142 142 52 218 142 97 * 218 17 18 19 20 21 22 23 24 25 26 27 28 Lab. F. Hours** 334 142 * 97 * 142 142 218 97 142 *A11 samples discarded at the end of 334 hours, marked with a star were not foul at this time. Samples **Time required for glue to develop an offensive odor. TABLE 6. Typical results obtained by methods recommended in appendix. u 158 155 239 157 299 218 160 175 166 273 272 153 174 *Peter Cooper Co.'s standard, 1%. **Peter Cooper Co.'s standard, l*/4. ***Bureau Aircraft Production standard sample. s si cO g QJ I-H 1 I 3 "S 1*2 Id >> 4J . S | ^ W T3 C t*=3 C Q) ll 2 bo ^ O 05 >s U 5^ 2 ft j3 c CC ^ ~ tin ^* "QJ TH > < oS 1 ! > 0^ > ^^ 5, ui < CUfa 1 o 13 t7 . 1.62 i-s-o 222 ll 2 ' - Z 10% 4 4 !2l 12 12 4 4 24 24 36 34 37 35 19 21 9 1.70 . 2.00 . 1.92 . 2.90 . 4.98 . 4.14 . 5.48 219 267 256 315 356 338 416 2 2 2 2 4 121/7 17 13 42 59% 4 4 4 4 4 14 % 26% 36 48 66% 4 4 4 4 4 24 48 44 66 198 *In this test the specimens were kept at 90 per cent humidity for 120 hours (5 days). fThis is a vegetable glue. Specimens of V 8 -inch birch veneer were glued two- ply with the grain parallel, and with one square inch of glued surface. The specimens were suspended in a humidity chamber with a 1-pound weight hung on each, and the time required for failure of the glue joint was noted. Tests one and two were made at 98 per cent, humidity. In test three the specimens were kept at 90 per cent, humidity for 120 hours, when the hu- midity was raised to 98 per cent. No failure occurred at 90 per cent. The temperature was about 80 deg. Fahr. CHAPTER XIV. USE AND APPLICATION OF THE GLUE HYDROMETER. A GLUE hydrometer is an instrument for meas- uring the density of glue solutions and ex- pressing the results in terms of the density of water, or in some scale such as Baume degrees THE GLUE that in effect also express results in terms of the HYDROMETER. density of water. Since the density of both glue solu- tions and water vary with temperature, hydrometer readings must take accurate account of temperature. The glue hydrometer usually employed consists of a copper pot and a hydrometer arranged for temper- ature of 75 C., or 167 F. The melted glue is poured into the copper receptacle and the hydrometer is al- lowed to sink until it finds its position. Some experts employ what is known as Weinhagen's Hydrometer. This is provided with a thermometric correction scale at the top of the instrument, and this is always clear of the liquid when the hydrometer is immersed. The temperature must be adjusted accurately before mak- ing the determination. This instrument is used to determine water ab- THE sorption. It is also used when inspecting glue rooms, HYDROMETER determining the amount of water and glue used by DOES NOT SHOW immersing the instrument into the glue solution in THE QUALITY the tanks, cookers or glue pots. This also affords a OP THE GLUE - very good check on the loss due to evaporation. This instrument cannot be used to determine glue quality, as its readings have no bearing whatever on viscosity or adhesiveness. APPENDIX TO BOOK I MODERN GLUES AND GLUE TESTING METHODS OF TESTING ANIMAL GLUE IN USE AT THE FOREST PRODUCTS LABORATORY MADISON, WISCONSIN APPENDIX. METHODS OF TESTING ANIMAL GLUE IN USE AT THE FOREST PRODUCTS LABORATORY.* DURING the war all the glue for use in air- craft construction was tested by the Bureau of Aircraft Production inspectors at the Forest Products Laboratory, Madison, Wis. More than a million pounds of hide glue furnished by ten differ- OYER ONE ent manufacturers had to be examined before its MILL ION shipment to the various aircraft factories was permit- POUNDS OF ted. This is not the first attempt which has been made GLUE INSPECTED to introduce standards in the glue trade, but it is the BY THESE first instance in which the majority of the large manu- METHODS. facturers, as well as many of the purchasers of glue, have recognized the same standards and assented to the validity of the same methods of testing. The methods which were adopted were selected as being those of rational basis, direct practical bearing, simplicity and convenience. They are not ideal ; a few of them are scarcely satisfactory. Nevertheless, when properly applied and interpreted, they will enable the chemist to select and grade glue. The physical constants of glues and glue solu- tions cannot be measured with the same precision as those of most of the materials which the chemist is called upon to test. Glue is a substance of widely varying chemical composition and physical condition. Tests made upon it are profoundly affected by factors which are difficult to control. Time, temperature, colloidal condition and the effects of micro-organisms are unusually important in glue testing. The methods which were adopted are as follows: For accurate work the viscosity, jelly strength and jelly melting point determinations should be made upon a sample which has been carefully dried at a low temperature to constant weight. The precaution, how- ever, is frequently disregarded. *From paper prepared by Wilbur Lloyd Jones, senior inspec- tor, B. A. P. 90 MODERN GLUES AND GLUE TESTING Weigh out 50 grams of ground glue and add it to 250 c. c. of cold water. Allow the mixture to stand for two or three hours in an ice box and keep the breaker containing the mixture covered with a watch glass. Then place the breaker in the water bath and raise the temperature gradually to 60 C., stirring every once in DETAILED a while. Keep the watch glass in place when the mixture METHOD FOB is not being stirred in order that the moisture which es- VISOOSITY. capes from the solution may be condensed. When the lumps have disappeared from the solution, recover the drops of condensed moisture on the watch glass and strain the solution through a piece of cheese cloth or wire gauze. Then cover once more with the watch glass and allow the solution to remain in the water bath until the temperature of the water in the annular ring of the viscosimeter is about 60 C. An Engler viscosimeter is used. Place a 200 c. c. viscosimeter flask underneath the orifice of the viscosimeter. Then pour the glue solution into the cup of the viscosimeter until it just covers each of the three level points, and adjust the thumb screws on the stand of the viscosi- meter so that the instrument is perfectly level. This should be done as quickly as possible in order that loss of moisture from the solution will be at a minimum. Then place the cover on the viscosimeter, insert the thermometer and regulate the temperature so that the glue solution in the cup is exactly 60 C., and the water in the jacket is somewhere between 60 and 61 C. Then remove the wooden plug with one hand and snap the stop watch with the other, and allow the glue solution to flow until the meniscus is exactly opposite the 200 c. c. mark on the flask. Then snap the stop watch again and note the reading. The viscosity of the solu- tion is the number of seconds required for 200 c. c. of solution to flow at 60 C. through the standard orifice of the viscosimeter. Before making a second deter- minAtion, clean out the apparatus thoroughly and be sure that no glue remains in the orifice, nor on the wooden plug. The tests for odor, reaction, foam, jelly, melting point, and grease should be made on the residue left from the viscosity determination. The odor is determined by smelling the liquid. METHODS OF TESTING ANIMAL GLUE 91 Take a piece of red and a piece of blue litmus and THE REACTION. dip both into the glue solution. Remove them and examine for change of color. If the blue litmus turns red or reddish, the solution is acidic. If the red litmus turns blue, the solution is alkaline. Glue solutions are usually either slightly acidic or neutral. The glue solution is then placed in a water bath FOAM. and heated to 60 C. It is agitated by a stirrer at- tached to a small electric motor for exactly one min- ute, after which time it is allowed to stand for ex- actly one minute. The height of the foam is then measured. The residue is then warmed up once more in the GREASE. water bath and a small quantity of an aqueous solu- tion of a dye is added to it. A brush is then care- fully cleaned until it is free from every trace of grease. A test is made on the brush by dipping it into a small portion of a dye solution and painting a broad streak upon a clean sheet of unglazed white paper. If the colored streak is free from spots where the color has been repelled from the paper, the brush is sufficiently clean to proceed with the grease test. The brush is placed in the glue solution now colored with dye and several streaks are painted upon clean unglazed white paper, employing a moderate amount of glue solution in the brush each time. The number of "eyes" in the colored streaks indicates the amount of grease in the glue. (See pages 33 and 34.) The instrument which is in use at the Forest Pro- JELLY ducts Laboratory, Madison, Wisconsin, for determin- STRENGTH. ing the jelly strength of glues, is a modified form of an apparatus which is used for the same purpose in the laboratory of one of the large glue manufactur- ing companies. It is essentially a "float" which rests lightly on the surface of a jelly, and a "plunger," to which is attached a scale by means of which the depth of pen- A NEW METHOD etration, or rather, depression, can be measured. FOR JELLY The "float" is made of brass plate. It should not STRENGTH. weigh more than 200 grams. The bottom surface, which comes in contact with the jelly, should be rather large, in order to distribute the weight and to prevent 92 MODERN GLUES AND GLUE TESTING the float itself from depressing the jelly to any appre- ciable extent. At the top of the "float" there is a guide of rectangular cross section through which the standard or scale of the "plunger" moves freely. An inverted trianguler section (1 c. m. in altitude) is cut away from the top of the front face of this guide, and the resulting diagonal line is divided into 10 equal parts in order to enable the operator to read the depression of the standard to tenths of a centimeter, and to esti- mate it to hundredths. THE PLUNGER. The nose of the "plunger" is hollow so that it can be filled with shot, and the weight of the plunger alter- ed at will. The hole through which the shot are added or withdrawn is closed with a screw. The standard is graduated in centimeters, and the zero mark on the standard is located at that point which is opposite the zero mark on the graduations on the "float" when the nose of the "plunger" is resting on a perfectly level surface. These details are explained in Fig. 17. This instrument, when used to test 12 to 1 jellies, has been found to be very delicate if the total weight of the "plunger" is 250 grams. To raise the weight of the "plunger" to this amount, a brass weight, a drawing of which will be found in the plan, will have to be placed on top of the nose. In making jelly tests, this apparatus is used as follows : Exactly 25 grams of ground glue are added to 300 c. c. of cold water. The mixture is stirred, covered with a watch glass and allowed to stand in an ice box for two or three hours. At the end of this time the mixture is placed in a water bath and heated grad- ually to 60 C., stirring frequently but keeping the beaker covered with the watch glass to prevent evap- oration. When the solution is free from lumps, the condensed moisture is returned to the solution and the . glue is poured into a crystallizing dish of standard size and shape. A dish which is S 1 /^ inches in diameter and 2 inches deep will be found very convenient for this purpose. The depth of the layer of glue in the crystallizing dish should be exactly the same in every case. The crystallizing dish with its contents is then METHODS OF TESTING ANIMAL GLUE 93 94 MODERN GLUES AND GLUE TESTING DETERMINING JELLY STRENGTH. KEEPING QUALITIES. JELLY MELTING POINT. placed in an ice box at from 5 to 10 C., for 12 or 15 hours. At the end of this time it is removed and the jelly strength of the glue is determined immediately. This is done by comparison. A sample of standard glue should be treated in exactly the same way as des- cribed above and at exactly the same time as the glue which is being studied. The glue being tested and the standard should be removed from the ice box at the same time and the jelly strength first determined by pressure with the fingers. Then the brass jelly tester should be employed and 3 or 4 readings of the amount of penetration determined. Obviously the weaker the jelly the greater will be the depth to which the plunger will penetrate. The depression of the 250-gram plunger against the resistance of the jelly is measured in millime- ters, and compared with the corresponding depres- sion of the plunger in the case of the standard glue. The consistency of the jelly is obviously inversely proportional to the depth of depression. This, of course, is true only in a more or less crude way; it is not an exact mathematical relationship. This test will be found to be as delicate, if, in- deed, not more so, than the so-called finger test. Jelly strength is expressed in percentages and it is equal to 100 times the amount of penetration in the standard glue divided by the amount of penetration in the glue being tested. The jelly resulting from the above test is then allowed to stand uncovered in the laboratory at room temperature for 48 hours, at the end of which time the skin on the surface is broken and the odor of the jelly is noted. Even after 48 hours the odor should be sweet. To determine the melting point of a jelly the fol- lowing procedure is employed: A 12-inch length of 6-millimeter glass tubing is bent in the middle so as to form a U-tube. A drop of hot glue solution (5 parts of water to 1 of glue) is introduced into one arm of the U-tube. A stirring rod or a medicine dropper can be used con- veniently for this purpose. If a 12-to-l jelly were METHODS OF TESTING ANIMAL GLUE 95 used a more sharply defined melting point might be obtained, but its behavior would be farther removed from the concentrated solutions which are used in gluing practice, and it would accordingly be of less DETAILS OF significance. When the drop of glue has sunk to a MELTIXG certain mark which has been etched half way down POINT ^ one side of the tube, the opening of the other arm is closed with the fore-finger, and the tube quickly plunged in ice water. The glue will now be found to be stationary, a cylinder of jelly exactly opposite a fixed mark on the tube. It is important that there should be no glue in any other part of the tube, be- cause it might clog the bore and subsequently prevent the free movement of the cylinder of glue. The U-tube with its cylinder of jelly is allowed to stand about an hour at 10 to 15 C. It is then immersed in a beaker of water (10 to 15 C.) to such a depth that the glue is beneath the level of the surface of the water. The temperature is then slowly raised and the water stirred constantly. The tube is fastened to a sensitive thermometer by means of rubber bands. At a certain definite temperature the cylinder of jelly will commence to slip from its position, sink- ing slowly at first. The temperature at which movement is first noticeable is taken as the melting point. The heat communicated from the walls of the tube melts the surface of the cylinder of jelly which is in contact with it, thereby allowing the jelly to fall of its own weight. Glue jelly is a very poor conductor of heat. Conse- quently, other methods which require the thermal penetration of a considerable mass of jelly will be handicapped on that account. The adhesive or strength test is carried out as follows : A piece of hard maple is cut into two ADHESIVENESS. halves of the size and shape indicated by the first specimen in Fig. 6. Dense, hard, straight-grained, thoroughly seasoned wood, free from defects, should be used. Preferably it should be flat-sawed lumber. The two blocks should be put through the planer and then over the jointer. The surfaces which are to be placed in contact should be absolutely flat, and they should fit perfectly. The moisture content should be 96 MODERN GLUES AND GLUE TESTING PREPARATION OF BLOCKS FOR STRENGTH TESTS. GLUE APPLIED AT FOUR DIRECTIONS. PRESSURE MUST BE MODERATE. between 6 and 13 per cent. It has been found unneces- sary to warm the test blocks above the temperature of the room. Moreover, it is undesirable, because even a moderate heating is liable to distort the blocks to a certain extent and prevent them from fitting together perfectly. It is a good plan to test every unknown glue at four different water^glue ratios. With a moderately high grade glue, such as Peter Cooper's Standard No. 1, sets of specimens should be prepared, using 2, 2^4, 2 l /2 and 234 parts of water respectively to one part of glue. It might be advisable in the case of an exceeding- ly high grade glue to prepare a test block at 3 to 1, and there are low grade glues which will give best results with less than 2 parts 6f water to 1 of glue. The glue solution should be used as soon as pos- sible after it has melted and attained a temperature of 140 to 150 F. The glue should be applied freely to both of the surfaces which are to be joined. It often helps considerably if the hot glue is brushed well into the wood, to assure proper penetration by the glue. The blocks should then be allowed to stand until the glue has thickened a little, but they should not stand long enough for the glue to "set." If the glue is touched from time to time by a finger which is rather quickly withdrawn, there will come a time when fibers or strings of glue an inch or two in length will be pulled up from the surface. When this point has been reached, the two blocks should be joined, rubbed to- gether slightly with light pressure, and then placed in a press designed in such a way as to assure an even- ly distributed pressure. As soon as possible the pres- sure should be applied. It should be a moderate pres- sure, just sufficient to bring the edges of the glued surfaces into approximate contact. It should be re- membered that for testing purposes it is better to em- ploy too little pressure than too much. By working rapidly one can prepare joints at four different concentrations for any glue, stack them in the press so that they will all be subjected to the same pressure, and finish the adjustment before the joint which was glued first has been "set." METHODS OF TESTING ANIMAL GLUE 97 These joints should be left in the press for at least 15 hours. They may be then removed and placed in a drying rack, where they should remain for at least six additional days. At the end of that time they may be cut into shear blocks, as shown in Figs. 5 and 6. These shear blocks are then tested in an Olsen Universal Testing Machine (Fig. 8), provided with a special shearing tool as shown in Fig. 7. The load should be applied at a rate not to exceed .025 inch per minute. A shearing strain is brought to bear on the layer of glue between the two wooden halves of the specimen. At a certain load each shear block will fail, and the failure will be either in the glue, in the wood, or in both. The load at which failure took place and the exact area of fracture are measured. The shearing stress in pounds per square inch can then be calculated. It is obvious that, whenever the failure occurred in the wood exclusively, the glue would have resisted a force somewhat greater than the one applied. It is only when the failure is in the glue entirely that its shearing strength has been fairly determined. It is more than probable that the higher the percentage the amount of failure in the wood assumes, the FAILURE HAS greater will be the disparity between the actual SIGNIFICANCE. strength of the glue and the load at which failure took place. A specimen which failed at 2,000 pounds per square inch, 90 per cent, of the fracture being in the wood, might indicate a stronger glue than one failed at 2,500 pounds per square inch where only 10 per cent, of the fracture was in the wood. Book II GLUE ROOM EQUIP- MENT AND THE USE OF GLUE BY C. MORTIMER BEZEAU Book II TABLE OF CONTENTS CHAPTER XV Preparing the Wood for the Glue The Lumber Storage Test for Dryness Warming the Lumber Ideal Gluing Temperature 105 CHAPTER XVI Preparation of Core Stock The Core Stock Free from Checks Crossbanding Allowing the Crossbanded Core to Dry Right and Wrong Sides Conditions Affecting Thickness 109 CHAPTER XVII Preparing Glue for Use The Glue Mixer Soaking Glue Regarding "Cook- ing" The Glue Heater The Cleaning Vat^-Use of Pure Water Rainwater Soda in Water Use of a Glue Size Regarding the Changing of Brands 115 CHAPTER XVIII Ideal Surface for Gluing Hardwoods End Grain Edge Gluing Concave Edges 123 CHAPTER XIX Covering Capacity of Glue High Grade Glue Spread Costs Wastage Efficiency 127 CHAPTER XX Glue Room Equipment Modern Appliances Kinds of Cauls To Prevent Glue from Sticking to Cauls 131 CHAPTER XXI An Ideal Glue Room Ground Floor Location The Heaters Ventilation Drying Room Circulation of Air 135 CHAPTER XXII Evolution of Glue Room Practice History Progress Unsolved Problems Conditions in Europe 141 102 MODERN GLUES AND GLUE TESTING CHAPTER XXIII Glue and Finishing Departments Shifting of Responsibility Blisters Effect of Water on Veneers Loose Veneer An Example of Trouble Playing the Game Square 145 CHAPTER XXIV Veneering Scroll Work Regarding Designs Elimination of Difficulties A Lesson for Beginners Thickness of Veneer. 149 CHAPTER XXV Laying Fine Face Veneers Importance of Good Veneer The Redryer The Hot Box Taping Veneer Spreading the Glue Open Joints Use of Warm Cauls ... 153 CHAPTER XXVI Spreading the Glue Evenness is Essential Intelligence Regarding Foam Good Glue is Necessary 161 CHAPTER XXVII The Glue Salesman The Science of Salesmanship Know Your Line and Don't Knock the Other Fellow's Friendship Sales- Tests Enthusiasm Order Takers Competitors Service Kinds of Salesmen Advertising Form Letters and Trade Papers 165 CHAPTER XXVIII Buying and Selling Glue Purchasing Department Quality vs. Price Requisi- tionsRecording Tests 175 CHAPTER XXIX Paper Box Adhesives Selection of Glue Box Making Machines Silicate of Soda ... . 179 CHAPTER XXX Avoid Abuses Good Glue Glue Room Temperature Weighing Boiling of Water Correct Temperature Melting Freezing Co-operation 181 CHAPTER XV. PREPARING THE WOOD FOR THE GLUE. TO obtain the best results in the glue room it is not enough that the glue be properly, prepared for the wood; it is equally necessary to have the THE LUMBER wood properly prepared for the glue. This prepara- SHOULD BE tion should commence early in the process of making PREPARED lumber as far back as the time when the tree is cut down in the forest. Trees should preferably be cut during the late fall and winter months, for at this time the trees are dormant and fairly free from sap. If the tree is cut down during the spring or summer months when it is in the growing stage the wood is very susceptible to atmospheric changes; and the con- tinual expanding and contracting of the wood is very detrimental to the life of a glue joint. Much of this dif- ficulty may be overcome by allowing the lumber to dry or season for several years. However, long air season- ing is no longer feasible, and kiln drying is usually re- sorted to. Every factory should have a place for storing lum- ber between the dry-kiln and the workshop. This storehouse should be well ventilated so that the air will STORED AFTER be occasionally changed fresh air entering from the LEAVING outside; which will give it the right humidity. The KILN lumber should be made quite dry in the dry-kiln before being placed in this storehouse, which should be kept at a temperature of about 60 degrees Fahrenheit, which temperature, together with the humidity in a properly ventilated place, will enable the lumber to so adjust itself that it will become less changeable in its nature and less prone to yield to atmospheric influ- ences, and, therefore, more dependable after it is worked up. In order to save extra handling of the lumber, tracks should be laid in the storehouse so that it may receive the loaded cars direct from the dry-kiln; and then in turn send them to the cutting-out department 106 PREPARING THE WOOD FOR THE GLUE TEST LUMBER FOR DRYNESS WARM THE LUMBER IF GOLD without any changes. If this cannot be done the lum- ber must be piled with strips between each layer the same as when piling for the dry-kiln. Lumber should always be tested for dryness before being glued up. If unfit stock be worked up it will never be made right and will always be a source of trouble. A method of testing lumber for moisture by no means uncommon is by carefully measuring the width, then heating it in an oven or hot-box and noting the amount of shrinkage. But this is not a safe test. The better method is to weigh a small piece on a very sensi- tive scale ; and after heating in an oven at about 215 F., for twenty-four hours, note the change in weight. Before weighing the second time the board should be allowed to cool to the same temperature as when it was first weighed. Heating in the oven should eliminate the last particle of moisture and the difference in weight before and after heating should give the percentage of moisture which the lumber contains. Lumber should never be glued up when cold, whether it be edge jointing or veneering; and whether it be animal or vegetable glue that is to be used, it will be safer to warm the wood if it is cold. This is due to the fact that the cold glue solution, or one that is chilled by cold wood, is too viscuous to permit the glue to enter the pores and obtain a hold. However, care must be taken not to overdo the heating. The best re- sults are obtained between 80 F. and 95 F. All things must work in harmony in order to pro- duce the best results, and the temperature of the room in which the work is done must be in harmony with the required temperature of the wood, as well as the temperature of the glue. There was a time when a great many people had the idea that the higher the temperature of the glue-room the better; with the result that the temperature was such as to be detri- mental to the health of the workmen. All this was in harmony with the other mistaken idea that glue itself had to be prepared and used at a high temperature. But careful experiments show that a temperature suit- PREPARING THE WOOD FOR THE GLUE 107 able for the workmen is suitable for the work. Such a temperature is from 70 degrees to 75 degrees Fahren- heit. While this temperature is sufficiently high, under AN AVERAGE no circumstances should the glue be used at a lower TEMPERATURE temperature. It is not enough to have the glue hot and wood warm, because the cold air will chill the outer surface of the spread and impair its power of adhesion. The temperature here indicated is the one to be maintained at the point of contact between the air and the glue. For this reason the thermometer should be on a level with the glue spreader and veneer-laying bench. A few feet in height frequently makes a differ- ence of several degrees in the temperature of the air, especially during the period of early morning heating before the warm air has been diffused uniformly through the whole room. For this reason, if the ter- mometer is placed higher than the point of contact be- tween the air and the glue, one is liable to begin opera- tions in a temperature several degrees lower than that required, thereby injuring the work without know- ing it. With the temperature of the air at 75 degrees Fahr- enheit, the wood at 95 degrees and the glue at 140 de- IDEAL grees, we have that ideal combination which, every- GLUING thing else being equal, will insure the best possible COMBINATION results. CHAPTER XVI. PREPARATION OF CORE STOCK. IN the process of building up reinforced wood bodies for pianos, furniture, automobiles and interior trim there is what is called a "core," or center ; the proper preparation of which is of great importance to the finished article. This center, being the foundation of the structure, must be right ; otherwise the quality of the finished article will be defective. It has been THE CORE thought by some that the core being covered by outer layers requires little attention, as all defects in mate- rial and workmanship are hidden from view, and will never be revealed, but a greater fallacy can scarcely be conceived. Of course, this core does not require the same high quality of material that is needed for the outer, or face layer; but the contention that anything is good enough for corestock is the one we wish to combat. Core stock should be sound, and may be of almost any kind of wood grown on this continent ; the kind to be used depending entirely on the use to which the finished article is to be put. Because of its strength and shock-resisting powers Sitka spruce is used for airplane work ; while in the manufacture of furniture and pianos the wood selected is usually such as will approximately match the texture of the veneer or crossbanding with which it is to be united; although quite frequently cost is the prime factor in determin- ing the kind of wood used for this purpose. But less depends on the variety of wood than on its preparation for the work in hand. When we say that wood for core stock should be sound we mean free from checks of various kinds. CORE ST There is a great deal of wormy chestnut used for this SHOULD E] purpose, and to this there is no serious objection un- less it is so badly eaten as to destroy the surface for the glue ; and this is hardly conceivable. Only one variety of wood should be used in each 110 MODERN GLUES AND GLUE TESTING CORESTOCK SHOULD BE DRIED CROSSBANDIXG FACE VENEER IS THIN core. If two kinds of wood are glued together in one core, say, basswood and birch, there is sure to be trouble which may not show itself until after the goods are finished. The swelling of these two woods as a re- sult of the action of the moisture from the glue will not be in unison; neither will the shrinking be uni- form ; and an uneven surface will result in consequence. After the core stock has been glued up it should be sent to the drying room in order that the joints, which have swollen from the action of the water in the glue, may shrink back to their normal position. If they are not allowed to dry out properly before being planed there will be more than the proper amount of fiber re- moved from the swollen joint, with the result that when the joint has dried out it will have shrunken be- low the level of the surrounding wood; and the depression thus made will show after the stock is fin- ished, unless a very heavy crossband has been used. For the better grade of work core stock is always crossbanded. This crossband consists of a sheet of wood glued on each side of the core, with the grain of the one running crosswise of the grain of the other; the object being to reinforce it to prevent checking, twisting or warping. It is the practice in some shops to lay this crossbanding at the same time that the face veneer is laid ; but this plan is not here recommended, nor is it followed in the best shops. The plan adopted by those who have the best quality of work in view is to lay the crossbanding by itself and, after taking from the press, pile it away in the drying room with strips between each piece to dry out before laying the face veneer. Laying the crossbanding in advance of the face veneer has several distinct advantages over the laying of both at the one time; chief of which is the better opportunity it affords of properly preparing the sur- face for the face veneer. Fine face veneer is usually cut very thin, and any unevennes in the surface to which it is glued will be reffected through it after the stock is finished, and will detract considerably from the quality of the goods as well as add to the cost 01 PREPARATION OF CORE STOCK 111 finishing. Crossbanding, on the other hand, is usually cut much heavier than veneer intended for face work, and is rotary cut ; that is, it is sliced, or peeled off the outside of the log as the latter is revolving in a lathe. The method of cutting crossbanding makes it difficult to get a surface sufficiently smooth for fine face veneer without some cleaning up; and this cleaning up can best be done after the crossbanding has been fastened to the core. Allow the crossbanded cere to remain in the drying room a sufficient length of time to become properly dry before doing anything toward cleaning it up ; other- ALLOW THE wise there is danger of weakening the glue-joint. The CROSSBANDED length of time required for this will depend on the c< capacity of the drying room; but in a room such as that described elsewhere in this book, from three to four days will be sufficient to eliminate all danger of the cleaning-up process affecting the glue joint; and render it sufficiently dry to receive the face veneer. This cleaning-up is usually done by putting the stock through the sander. If the surface is in pretty bad shape, use two or more drums, with coarse paper on each ; no fine paper being used for this operation. It is better to use more than one drum for cleaning up, taking shallow cuts, rather than one drum and a deep cut, as the shallow cuts are less apt to affect the glue by heating. It is very important to have the crossbanding thoroughly dry before it is laid. There are some who have the idea that, while it may be important to have the face veneer dry, the condition of the crossbanding DRY is not a matter for any concern. These people have their troubles in consequence of their neglect in this connection; but they ascribe the cause to something else, and consequently they never find it, and, there- fore, do not remedy it. The writer has seen face veneer broken across the grain in consequence of being laid on crossbanding which has not been properly dried before it is laid. It was %-in. crossbanding and had checked in the process of drying after the face had been laid; and at the point of these checks it had exerted sufficient 112 MODERN GLUES AND GLUE TESTING DO NOT MIX STOCK RIGHT AND WRONG SIDES OF CROSS- BANDING RIGHT SIDE OUT force to rupture the face veneer above. What we have said about the importance of using only one variety of wood in a core applies with equal, if not greater, force, to the use of crossbanding ; for the nearer our work brings us to the point where the face veneer is to be laid, the more the necessity for care. If one has a lot of odds and ends of stock of vari- ous woods that he wishes to use up, it may be done by sorting the lot over and separating each kind of wood ; and if there is a difference in thickness, separating these, too. These should then be dried and cut to re- quired size, then taped ready for use. There is always a right and wrong side to rotary cut stock; and the thicker the stock, the more pro- nounced is this distinction. The right side of the -stock is that which was on the outside of the log during the process of cutting; and the wrong side is that which was the inside of the sheet as it was peeled off the log. To illustrate. Take a long, narrow piece of paper and bend it in a circle. The outer side of this circle of paper corresponds to the right side of the crossbanding, and the inner side to the wrong side as it leaves the log. Now straighten the paper out and note closely in your mind what follows. Imagine the paper to be %-in. more or less thick, and see the strain there is on the inside as we straighten it out. The strain is more than the fibers can withstand ; and they break and separate. This side with the ruptured grain and fiber is the wrong side of the stock. The crossbanding should always be laid with the right side out the wrong side being as far from the face veneer as possible. The right side is much more easily cleaned up ; and what is more, if the wrong side were left up, the ruptured fibers and resultant scales would be so affected by moisture from the glue and subsequent atmospheric changes that they would im- part a corrugated appearance to the face veneer. The right side of crossbanding is the side to be taped, so that the tape will be removed when cleaning up for the face veneer. But this applies only to cross- banding that is laid in advance of the face veneer. If PREPARATION OF CORE STOCK 113 the crossbanding and face veneer are to be laid at the one time the wrong side of the stock is the side which, in this case, should be taped, in order that it may be laid next to the core and as far from the face veneer as possible. The joint between the tape and the wood is not as firm and strong as a glue joint between two pieces of wood made under pressure. There is always danger of the tape coming loose hence the reason for having it laid as far as possible from the face veneer. As before intimated, crossbanding is cut in various thicknesses ; the thickness to be used to be determined by the nature of the work in hand. Crossbanding is done to add strength to reinforce the thing cross- banded; and unless the crossbanding is of a suitable thickness to match the core it will be a source of weak- ness and not of strength. If one is making thin panel stock to be made five- ply, in the very nature of things everything must be thin probably Va-in. core with 1/20-in. crossbanding and 1/30-in. face. But if one is making a heavy buffet top and crossbanded it with 1/20-in. stock he would very likely be building into it trouble for the future. Such thin crossbanding would not be a source of THICKNESS strength to a heavy top that needed to be reinforced ; OF THE and if not a source of strength, then it becomes a dan- CORE STOCK gerous source of weakness. Should such a core have a tendency to warp, such a thin crossbanding would be more likely to break under the strain imposed than to offer any effective resistance ; and if this happened, the last state of the top would be worse than the first. Nothing less than i/s-in. stock should be used for cross- banding l^-in. core; decreasing or increasing in thickness as the requirements of the core demand. CHAPTER XXVII. PREPARING GLUE FOR USE. THE task of preparing the glue required for the day's work should never be entrusted to a novice, but to a person of high intelligence and long experience. Much depends on how this work is done a mistake at this end of the line may prove disastrous to the whole output of the day. While a person of experience is preferred in the preparation of glue for use, any man of good intelli- gence with experience in its use can soon grasp the essential points and become proficient at the work. But it cannot be done in an hour, nor in a day, and for this reason every glue room should have an understudy who is qualified to take the place of the head glue mixer in the event of the latter being off duty. There is a difference of opinion regarding the ques- tion of soaking glue in cold water before heating it for use. Our modern glue-mixers have made it possible to reduce glue to the liquid state in a comparatively short time without previous soaking; at the same time the writer favors soaking first where this can be done without deterioration of the glue, as it is not good for the glue while in the dry state to be plunged into hot water, or even into a hot glue solution. But if the glue is put into the dissolver with cold, or even lukewarm water, and the temperature of the whole raised gradu- ally, no injurious effects will result, and previous soak- ing is, therefore, unnecessary. Much glue is injured in the process of soaking, especially in hot weather. It is put to soak too far in advance of requirements the process of decomposition GLUE IS sets in before it reaches the heater. If the glue can be INJURED kept at a low temperature while soaking, no bad effects IN* SOAKING will result from soaking over night, or even a few hours longer. If one has more glue soaking than will be required for the first three or four hours' work it would be much better to leave it in the cold soak than to 116 MODERN GLUES AND GLUE TESTING DO NOT MIX OLD AND NEW BATCHES put it in the hot heater, which would hasten the process of decomposition. Glue that is kept in the soak may be added to the heater at intervals as required; but it would be better to always empty the heater before add- ing fresh glue. The reason for this is : Heat deterior- ates glue, and the process of deterioration begins soon after a certain temperature has been reached. The change is very slight at first, nevertheless there is a change ; and if we add fresh glue with some of the old remaining, the deteriorating effect of the heat on the old glue is increasing until, by the end of the day, that which remains of the early morning lot has decreased in strength probably 50 per cent. I do not mean that all the glue in the heater has deteriorated to that extent only the original lot, which, being mixed with fresh FIG. 18 PREPARING GLUE FOR USE 117 glue, has saved itself from being rendered practically useless for permanent work; but saved itself at the expense of the glue that was added from time to time by distributing itself throughout the whole. There is always an advantage in having glue soaked ready for the heater, as, in case of emergency, one can prepare it in a very short time and more easily regu- late the supply for the day's requirements. And where one must soak the glue, some method for keeping it cool and prevent a lessening of its quality should be adopted. For this purpose a cupboard with shelves (Figure 18) on each of which is placed a coil of water- pipes with cold water running through them and on which the pans of soaking glue are placed, will keep the glue at a sufficiently low temperature to prevent injury within a reasonable time. The water which runs through these pipes need not be wasted, as it can be turned into the reservoir and saved for boiler purposes. The idea that glue must be "cooked" before it is "COOKING" is ready for use has long since been exploded. Time was UNNECESSARY when men thought that glue would not hold unless it was heated to the boiling point and kept there for some time all the way from one to three hours. And this was done, all unconscious of the fact that each minute of sustained heat was eating at the very life of the glue and lessening its adhesive qualities. In those days men talked of glue "cookers ;" but with the pass- ing of the cooking idea there passed away also the words which gave the idea expression; and in their place have come the words "heater" and "dissolver," which signify just what they are expected to do. While one must not cook animal glue in preparing it for use, it must not be used cold or at too low a tem- perature. There is a tendency on the part of some peo- ple to rush to the other extreme when the danger of A TH ERMOME- one extreme is pointed out to them. Some have rea- TER is soned that if heat injures glue, then the proper way to NECESSARY use it is cold ; and they have tried to do this, but with disastrous results. The proper temperature at which to use glue to obtain best results is 140 to 150 degrees 118 MODERN GLUES AND GLUE TESTING CLEANING VAT KEEP THE GLUE ROOM CLEAN Fahrenheit : and as soon as it reaches this temperature it is ready for use. Every glue heater should be equipped with a thermometer for registering the tem- perature of the solution. No matter what else one has or has not, a thermometer should be considered an in- dispensable part of the glue room equipment. As a preliminary to each day's operations the greatest care should be exercised the evening before in cleaning up all the glue room utensils. If these are not kept clean, tire stale glue adhering to them will become mixed with the day's preparation and set up a deterio- rating influence. For this purpose a vat, of the required size, filled with water into which the utensils may be placed to soak away the old glue, will be of great advantage; then in the morning they may be rinsed clean with clear water, which will take but a few moments. The vat should have a drain pipe at the bottom with a valve to facilitate cleaning, and should be emptied and refilled each day, otherwise it will soon become foul and offensive. Every glue room operator should contribute his share toward making working conditions as pleasant as possible. The glue room may be made a pleasant place in which to work if ordinary care is exercised, but if neglected it is liable to reach the opposite ex- treme. If the floors, benches and machines are kept clean from the start they will give very little trouble, as but little time is required to keep them clean if they are cleaned daily. But if they are allowed to go on for days, and sometimes weeks and months, daily accumu- lating fresh coats of glue, the condition will soon be- come such that no man with any regard for his per- sonal comfort or any knowledge of the rules of health would remain in the room longer than would be abso- lutely necessary. The benches should be scraped and the floor washed with hot water. A few minutes the last thing before leaving at night will make everything clean and sweet and put the room in such shape that one will not dread to enter it in the morning. The careful and economical glue mixer will keep in touch with the progress of the work in the gluing-up PREPARING GLUE FOR USE 119 department in order to know how much glue to keep in course of preparation, and not have any left over at the end of the day. In warm weather glue that has been left over from the day before will seldom be fit for use and is usually thrown away. There is a great quantity of glue wasted in this way, and it ought not to be. With glue soaked ready for heating, it would be a very small matter to prepare an additional lot, should the day's supply run out before the day is done, and there need be no hold-up of the work or time wasted. In view of this there is no excuse for having a quantity left over to be thrown away and wasted. Decomposition of glue is frequently hastened by the USE PU8E water with which it is mixed. If this water contains WATER organic impurities, the process of decay will com- mence as soon as the water and glue come together. The value of glue may easily be reduced one-half by the use of impure water. There are many things to be found in water which will injure glue. Water drawn from extremely deep RAIN WATER wells, as well as river water which flows over a lime- 1S GOOD stone bed, will frequently contain a sufficient quantity of lime or iron or other chemicals to seriously injure the glue. Some concerns that use a large quantity of glue have found the ordinary sources of water such a menace to their glue that they adopted the use of dis- tilled water for mixing purposes. Water from the boiler, or water into which steam from the boiler has been condensed ought not to be used for mixing glue. Most boiler compounds are injurious to glue, and con- densed steam from the engine is most certain to con- tain a quantity of grease or oil. Where it can be ob- tained, clean, fresh rain water should be used for mix- ing glue; or if this is not obtainable, some means should be adopted for purifying the water, either by filtering or distillation. Water containing an excess of lime may be purified by adding one-half pound of ordinary washing soda to a thousand gallons of the water. The effect of the chemical action produced by the soda will be the pre- S( DA WILL cipitation of the impurities to the bottom of the ves- P 120 MODERN GLUES AND GLUE TESTING PREPARATION 1 OF GLUE GRAIN OF THE WOOD sel. But one must be careful and not use the soda in a larger proportion than the above, as washing soda is an alkali, which, in certain proportions, would be in- jurious to the glue, and the last state would then be no better than the first. It is very difficult, except in the open country, to obtain rain water that is not impregnated w r ith impuri- ties, such as soot, etc., gathered from the air in its de- scent to earth. Such impurities may be removed by filtering the water through charcoal. Place several lay- ers of burlap in the bottom of a barrel or tank, over which place a foot or so of powdered charcoal, and let the water filter through this. The tank should be cleaned out at intervals, the length of which must be determined by the condition and quantity of water to be filtered. The proper preparation of glue for the wood-work- ing plant requires considerable knowledge; especially is this so in the preparation of glue for the veneer room. One must know the kind of glue he is using, also the kind of wood on which it is to be used. Different glues require a different percentage of water in their preparation, and different woods require a glue solu- tion of a different consistency. Hard, close-grained woods, such as maple and birch, do not require as heavy a glue solution as basswood or poplar, which, while close-grained, are soft and absorbent and will imbibe a lot of glue ; nor yet as heavy a solution as oak, which, while hard, is very porous and will absorb a large quantity also. Where one has to prepare a glue solution for one kind of wood, say, a hard wood or a soft wood, it is a comparatively easy matter ; but where one is called on to prepare a solution to meet the requirements of two ; the problem is perplexing, as one cannot have a thin and a thick glue both in the one solution. But the glue room is sometimes expected to do more than its share ; and this is one of the instances. As a matter of fact, one cannot prepare a glue solution that will meet the requirements of the two extremes of hard and soft woods unless these two woods will come part way and PREPARING GLUE FOR USE 121 partially meet the requirements of the glue. This diffi- culty is probably met with in the preparation of glue for the veneer room more frequently than anywhere else. As before said, where two kinds of woods are to be glued together, both glue and wood must go part way A PROBLEM to meet the requirements of the other. Suppose we are SOLVED laying a poplar crossbanding on a maple core. Here is a case where the core requires a thin glue and the veneer a comparatively heavy glue. In a case of this kind we will have to prepare the glue to meet the re- quirements of one of the woods, and prepare the other wood to meet the requirements of the glue. In this case the correct plan would be to prepare the glue to meet the needs of the soft veneer ; and prepare the hard marie core to meet the glue. This can be done by pre- paring a heavy glue solution for the veneer and rais- ing the fibers of the hard core by sanding with coarse paper. But let us reverse the situation and bring out a lot USING A of hard veneer to be laid on whitewood or basswood GLUE SIZE cores. For obvious reasons we cannot machine sand the veneer as we did the hard core in the other instance, and the process of hand sanding is too slow and expensive to be considered; so we will have to again prepare the glue to meet the requirements of the veneer, only it must be made thin this time, and face the problem of how to prepare the soft core to meet the requirements of the glue. The problem thus presented is solved by glue-sizing the soft core with a thin glue solution ; thus sealing up the pores and neutralizing its absorbant qualities. This glue-size should become quite dry before the gluing-up process begins. The proportion of glue and water to be used in pre- paring the glue solution for any wood is determined as much by the kind and quality of the glue as by the wood on which it is to be used usually, if not always, the proportion of water increasing with an increase in THE GLUE the quality of the glue. And in the preparation of glue SHOULD BE there should be no guesswork. The strength of the WEIGHED glue should be known as well as the requirements of 122 MODERN GLUES AND GLUE TESTING the wood on which it is to be used ; and the glue should be weighed and the water measured. I wish to empha- size the importance of weighing the glue, because in the minds of some, it is so much easier to measure glue than it is to weigh it; and they follow the course of least resistance. But a bushel of glue does not always weigh the same that is, one bushel of glue may weigh several pounds more or less than another bushel of even the same grade of glue the weight depending largely on the condition of the glue. A finely ground glue will rest more compactly in the measure than would be the case with coarse, flake, shell or cake glue, and, therefore, weigh more ; the weight increasing with the fineness. After one has ascertained the requirements of any given wood, as well as the proper glue solution to meet these requirements, he should make a memorandum of the facts and preserve the data for future reference; as it is not safe to trust to memory in a matter of such importance. This memorandum should contain all the known facts concerning the glue ; including the result of all tests, if tests of a specific nature have been made. The great range in the quality of different glues makes it inadvisable to frequently change the make unless one has a well equipped laboratory for testing the article. Even then the practice is a questionable one from an economical standpoint. When one has a glue made by a reliable concern that has met the requirements of the past there should be some greater BE CAREFUL reason than a mere desire to try some other kind be- IN CHANGING fore & change is made. If one has a laboratory for thoroughly testing glue it would be well to be always on the lookout for something' better and cheaper; and whether a proposition to change glue is advisable or not can be ascertained by testing a sample. But where there is no proper equipment for testing glue, the glue room operator is placed at a disadvantage each time a change is made, in that he must learn his glue all over again ; and perhaps spoil considerable work before he understands it. CHAPTER XVIII. IDEAL SURFACE FOR GLUING. E fact that there is such a thing as an ideal sur- face for gluing or one that is more likely to make a permanent job than another, has been recog- nized as far back as the time when all woodworking was done by hand ; for in those days the wood-worker had his toothing plane with which he made very fine grooves in the wood for the purpose of removing the smooth, polished surface made by the hand plane in the THE GLUE process of cleaning up the surface preparatory to the SURFACE gluing and laying of the veneer. Good glue will retain its hold for some considerable time on any good, clean surface; but where one desires a glue joint that will be permanent, and one that will outlive the maker, he should give special care to the preparation. The proper preparation of a surface for gluing is a comparatively easy matter today, because of increased facilities for doing the work. It is pretty generally recognized and admitted that the ideal surface is one that is perfectly level and on which the fibers of the wood are suffici- ently loose to allow the glue to penetrate and secure a firm hold ; at the same time not sufficiently so to allow the glue to accumulate in quantity and prevent any surplus squeezing out. In preparing such woods as maple and birch, and other hard, close-grained woods, the drum sander, with but one drum fitted with coarse paper, will prepare a _._ . - . 11* i -TI i HARD WOODS surface which, everything else being equal, will make a glue joint that will last away beyond the lifetime of the man who did the work. It may not always be convenient to use the drum sander for the purpose of preparing corestock for glu- ing; then the scraping machine may be used for the purpose. In fact, for some woods the scraper is prefer- able to the sander. For instance, such woods as oak or chestnut, which have hard and soft places, the sander is liable to press deeper into the soft places than into 324 MODERN GLUES AND GLUE TESTING GLUE SIZE END GRAIN GLUING EDGES TOGETH1 the hard; and an uneven surface will be the result. With the scraper it is different, as the cut will be uni- form over the hard and soft places. A special blade for this work is now made by some manufacturers of scrapers. Difficulty is frequently experienced in making a glue joint on end wood, or in gluing the grain side of one piece to the end wood of another. The cause of the difficulty is usually in the end wood, which absorbs all the glue. Or in cleaning up the end wood it may be polished too smooth; or in cutting, the saw may have burned it smooth and hard, which is likely to be the case with a hard wood like maple and birch and some- times even walnut. In this latter case the remedy is to remove the hard surface with sandpaper, rubbing suf- ficiently to merely break the polish. If the end wood is open-grained or otherwise of an absorbing nature it would be well to glue-size it to seal up the pores, using a thin glue for the purpose. This is advisable on such woods as basswood and poplar and even oak. The preparation of the glue joint between boards for building up corestock, or for other purposes, is equally as important as that for veneering. Here, as elsewhere, to insure a permanent joint the surface should not be smooth and hard. A good glue joint, that is, one made with a high grade glue and with the sur- face of the wood in an ideal condition, should never open under normal conditions. Of course, if a glue joint becomes soaked with water, unless it is a water- proof glue, it will open. But under what we may call the average condition the wood will break before the glue will give way. In addition to the proper preparation of the surface the edges of the pieces to be glued should not be made perfectly straight, but should be made slightly hollow to insure permanency. The writer was once consulted regarding the cause of open joints and on investigation found that the joints were being made slightly rounded that is, the boards were made slightly wider in the center than at the ends. The object being to facilitate IDEAL SURFACE FOR GLUING 125 clamping up, as only one clamp on each end of a four- foot board was being used; the argument being that there was sufficient spring in the center of the rounded board to take the place of clamps. But the man who conceived the idea of gluing up stock in this manner had overlooked a very important factor in determining the quality of the joint, and that is, the spring supplied to the center as a result of the ACTg BOTH rounded edge of the board was a permanent force, and WAY8 one which operated two ways ; for while it gave press- ure to the center when clamping up, it was forcing the joint apart at the ends when the clamps were removed. This force, together with the fact that the ends of a glue joint always dry out more rapidly than the parts farther in and which creates a strain on the ends which dry out first, was sufficient to draw the joints apart; in some instances breaking the wood in the immediate vicinity of the joint. An ideal edge for gluing up is one that is slightly hollow or concave; that is, when the two edges are placed together they will meet at the ends only, gradu- ally and slowly separating toward the center. This requires more force and more clamps to bring the edges together than is the case with the rounded edge ; and although the spring or force resulting from the NCAVE concave edges is a permanent one, it is evenly dis- EDGE Zl tributed from the center to the end, and is so located that it is comparatively harmless. In any event, the strain is in the center and far away from the ends, where glue joints usually open. Not only that, but it is a positive help to the ends, as it increases the pres- sure of each piece toward each other at these points instead of away from each other, which tends to permanency. CHAPTER XIX. THE COVERING CAPACITY OF GLUE. EVERY manufacturer, regardless of line, is inter- ested in the covering capacity of the glue, for it is this point, all other factors considered, that determines the cost of the glue. We know that high- grade glues will take more water than low grade; on the other hand, high-grade glues would prove too ex- pensive for certain purposes, as, for instance in the HIGH GRADE manufacture of paper boxes. Again, one would not GLUES SET use high-grade glues in veneering, regardless of cost, T QUICKLY because they set too quickly. We know that liquids hav- FOR VENEERING ing the same specific gravity will cover the same amount of surface. Also, as has been previously ex- plained that glues can be prepared to give the same viscosity tests (varying proportions of water and glue) , hence, the liquids being the same, they will cover the same amount of square surface. The following table was published in Glue, June number, 1911. COVERING CAPACITY PER 1 POUND DRY GLUE OF STANDARD AMERICAN GLUE GRADES (BASED ON PETER COOPER GRADES): Yield of Liquid Glue Covering in Glue Grade. per 1 Ib. Dry Square feet. A Extra ........................ 3.65 79 1 Extra ......... _ ............. 3.45 75 1 ....................... _ ........... 3.34 72 IX .................................. 3.08 67 COVERING - 2.94 64 CAPACITY 1% ....................... _ ....... 2.82 61 1% ................................ 2.68 58 1% ................................ 2.55 55 1% ................................ 2.43 53 1% ................... - ........... 2.31 50 2 .................................... 2.19 47 It is to be regretted that glue prices have been so uncertain, and will likely be so for some time to come that we cannot cite a correct example as to possible savings, however, one can easily figure differences in 128 MODERN GLUES AND GLUE TESTING DETERMINE THE SPREAD COSTS MUCH GLUE IS WASTED the spread costs from the figures given in the table. For example, A Extra will with 1 Ib. dry glue cover nearly 70 per cent more surface than can be covered with 1 Ib. dry glue of the grade No. 2. The writer has always advised his clients to deter- mine the cost of spread from the cost records. The cost scheme should show the number of square feet covered in your veneering, joint, or to whatever line or use your glue has been applied. You know or should know the amount of glue used, and this will give the spread cost. Having established a fairly accurate amount, use this glue as a standard in future spread tests or comparisons. This can be done in a fairly safe measure by comparing viscosities. Someone may ask the question, "Why not deter- mine the glue spread from laboratory tests, dissolving a certain quantity of glue and determining the surface covered ?" My answer is, we may select the finest and most economical glue that money can buy, but unless the gluing department is right and the men apply and use glue correctly our spread test would avail us noth- ing. Your records should show what your glue costs are, and this is the real check on your gluing depart- ment. We will find some glue rooms equipped with the old style glue pots and the glue applied with a brush. We will find other modern rooms employing the latest types of glue-spreaders and find they cover a greater surface than the men daubbing the stock and likely wasting from ten to fifty per cent. If the surface of the stock covered is accounted for, the glue buyer will know that something is radically wrong. Yes, it is well to get a line on your spreading by testing, but in the name of common sense do not depend upon these tests. Suppose you buy a glue worth, say, thirty cents. It passes the required tests and is a pure hide product. The men in your glue room, however, abuse this prod- uct by overheating so that when actually used it is worth but twenty-five cents. What good was derived from your tests? Why not buy the twenty-five cent product in the first place and save the five cents that you are actually wasting? Therefore, our tests and the THE COVERING CAPACITY OF GLUE 129 actual final result must be considered. When you know beyond the shadow of a doubt that your glue is prop- erly used and you are getting one hundred per cent glue room efficiency then you can apply the informa- PER CENT tion given regarding the spread of glue, but until this EFFICIENCY? degree of efficiency has been attained, your assumed spread cost is unreliable and cannot be depended upon. 130 MODERN GLUES AND GLUE TESTING FIG. 19 CHAPTER XX. GLUE ROOM EQUIPMENT. COMING to the practical end of the use of glue, we would say that in this day of rapid processes one must have a modern, up-to-date equipment in order to obtain best results. It is true that some very fine work was done in the olden times when the glue MODERN pot and brush, and the clamps or hand press comprised GLUE ROOM the entire glue room equipment, and the glue brush APPLIANCES and pot had to compete with the glue brush and pot; and the clamps and hand presses had to compete with the clamps and hand presses. But times have changed ; and one might as well expect the old stagecoach to com- pete today with the modern railroad flyer, or the old hand sickle to compete with a modern harvester, as to expect the old fashioned glue room equipment to com- pete with modern appliances. It is not merely a ques- tion of quality of work ; but in these times of keen com- petition time and cost are important items. Nor is this all. To do the amount of work demanded of the modern glue room in one of our large modern factories to do this amount of work with the old style equipment would require almost as much space as is now taken up by several departments; and in most factories floor space is an important matter. Glue room equipment has kept pace with the on- ward march of progress in other spheres of activity a steady march toward greater efficiency. All the changes that have been made in means of doing the work in the glue room have been for the purpose of making it easier to do the work in less time, and in- crease the quality where possible. The checking of veneer, owing to the presence of moisture before lay- ing, created a demand for the redryer; and the ten- dency of dry veneer to rapidly absorb moisture from the glue created a demand for something more rapid than the hand press, and the hydraulic press came into existence (Figure 19). The same may be said of the 132 MODERN GLUES AND GLUE TESTING other modern machines. The retaining clamps and the overhead carriers came in response to a demand for economy in floor space, and to enable the one power press to do the work of many. The glue spreader (Fig- ure 20) responded to a hurry-up order froni the power press to keep it busy, as men could not spread glue fast enough with the brush. Then the modern glue dis- solver came to prevent these rapid machines from FIG. 20 GLUE ROOM EQUIPMENT 133 standing idle while glue was being prepared during the early part of the day. It is not enough that work be done well it must be done in the shortest possible time and in the easiest possible way ; and this can be done only by the use of the best equipment. Every manufacturer is anxious WORK MUST that the cost of operating his glue room be reduced to BE DONE IN the lowest possible point consistent with good work, THE SHORTEST and the result of our observation is a firm conviction POSSIBLE that the shops with the lowest operating expense are T those with the best equipment. The first cost of the plant is undoubtedly greater, but the difference be- tween a poor and a good equipment is soon wiped out by the saving in operating expense and the decrease in the cost of repairs. It is not our purpose to advocate any particular equipment, as every factory must be governed by its individual needs ; but we have been asked so often re- garding the best kind of caul for use in the veneer room that we might be permitted to say a word about this part of the equipment. There are three kinds of cauls in general use, i. e., wood, metal and fiber board. There are three kinds of metal cauls, i. e., iron, zinc and KINDS OF aluminum. It is not for us to advocate the claims of CAULS any of these, as many glue room operators have had success with all of them. But we will say that metal cauls should always be used where hot glue is the adhe- sive, because they will absorb and retain heat more readily than wood or fiber ; while we have a preference for fiber cauls where a cold glue is used, because they are light in weight and easy to handle. We have been frequently asked how best to prevent glue from sticking to cauls. In the case of fiber cauls they may be made glue-proof by repeated applications T o PREVENT of hot parafine oil into which parafine wax has been GLUE FROM melted in proportion of one pound of wax to a gallon of STICKING oil. Heat the oil as hot as can conveniently be done and T0 CAULS apply it until the caul will take in no more. The idea of the wax is to add body to the oil. A caul thus treated will last for a considerable time without anything further being done to it ; but to keep it in prime condi- 134 MODERN GLUES AND GLUE TESTING tion it would be well to give it a light application of the oil at intervals, the length of which will depend on the frequency with which the caul is used. Metal cauls need something with a little more body than oil. Parafine wax has been used by some with fair success; but beeswax is better. For this purpose it is not necessary to use the genuine beeswax, as there is an artificial article that will answer the purpose equally well. With all cauls care should be taken to keep them clean ; and care should be taken in cleaning them. It is not a good plan to scrape cauls in cleaning, as this is liable to wear them thin in places, resulting in a reduced pressure at these thin points when in the press, which, in turn, results in blisters in the veneer. Metal cauls may be cleaned with steam or hot water, if one has a vat of hot water to put them in ; or they may be washed off with a rag and hot water. With fiber cauls there is less liability of the glue adhering to them, owing to their thorough saturation with oil, and if any does adhere it can easily be rubbed off. But cauls should always be examined for glue be- OAULS SHOULD fore being used, as any particles which may be present BE EXAMINED w ju k e pressed into the veneer, leaving dents which will likely rise and give no end of trouble during the process of finishing. CHAPTER XXL AN IDEAL GLUE ROOM. TO GET best results in the use of glue, whether it be in gluing up solid lumber or in making veneered stock, one must have a proper place in which to do the work. A glue room located in a base- ment with a seven or eight foot ceiling is not conducive to the best in glued-up work; and this for more than one reason. Such a place is unfit for the work ; and a man capable of doing good work under proper condi- tions can easily find plenty of employment in more con- genial surroundings, and, therefore, is not likely to remain in such a place. An ideal glue room for doing veneer work is one located on the ground floor, because the light so neces- sary for matching fine veneers is better here than it is at a higher altitude; but for other purposes it is im- material whether it be located there or on the second floor. If located on the ground floor, and the floor is SHOULD SB cement with no basement beneath, it should be raised LOCATED ox to prevent dampness. GROUND The work of matching veneers and preparing the stock for gluing should not be done in the glue room proper; but should be done in a room immediately adjoining. In this room should be the machines for cutting the veneer to size and jointing and taping. Also immediately adjoining the glue room should be the drying room ; the nature and importance of which we will consider later on. The size of the glue room must, of course, depend on the volume of work to be done, but in laying it out it would be well to make provision for an expansion of business in order to avoid hampering the work through congestion. The success of a glue room depends a great deal on the arrangement of the equipment. If the work of glu- ing up the solid stock is done in the same room with the 136 MODERN GLUES AND GLUE TESTING LOCATION OF THE GLUE HEATERS SATISFACTORY HEATING ARRANGEMENT veneering, the appliances for doing the different work should be so separated that the work of one will not at any time interfere with the work of the other. As far as possible the revolving clamps and presses for the solid lumber work should be located at the side of the room to that where the veneering is done, leaving the space between the two equipments for stock in process. The glue heaters should be placed in one corner of the room with the glue spreader immediately in front of them. The heaters should be sufficiently elevated to allow the glue to flow into the upper and lower tanks of the spreader. This is preferable to carrying the glue from the heater to the spreader in buckets, which is liable to chill the glue and impair its quality. The glue should be run from the heater to the spreader through a detachable pipe ; and this should be taken down each night and cleaned along with the other utensils. The veneer laying bench should be placed in close proximity to the spreader and the power press as close to this as is practical, to avoid unnecessary carrying of the stock. Near the heater is a vat into which the uten- sils are put to soak to facilitate cleaning. This vat is provided with a drain-pipe and valve to allow empty- ing every day. The heating of the glue room is an important mat- ter. The forced hot-air system is not here recom- mended, as there is too much danger of the draft com- ing in direct contact with freshly glued surfaces and impairing the adhesive quality of the glue. The over- head steam coil is not recommended, because it heats the part of the room first that least requires it, and the part toward which the hot air will move in any event ; and in addition to this it is hard on the workmen. The most satisfactory system for heating will be found to consist of one or more coils of pipes placed along the walls about one foot from the floor, the number of pipes to the coil to be determined by the space to be heated, as well as the length of the coils. A well conceived glue room will have plenty of head room. Where animal glue is used, the odors are not of the most pleasant sort at the best of times, but are par- AN IDEAL GLUE ROOM 137 FIG. 21 138 MODERN GLUES AND GLUE TESTING A FAN SHOULD BE USED THE DRYING ROOM ticularly nauseating in a room with a ceiling so low that one feels as though he were in the midst of com- pressed offensiveness. No glue room should be less than eighteen feet high, and then a fan should be in- stalled for carrying off the foul air. This fan should be located near the ceiling at the opposite end of the room to the one where the spreader is in operation, and should revolve so as to draw the air out. This can be done without disturbing the air at any one point suf- ficiently to create a draft. Drawing air out with a fan is different from blowing air into a room by the same means. In the former case the air which is drawn out of the room is taken from the top and the air in all parts of the room moves upward to take the place of that which is being carried away. The movement of the air is so slow and even as to be imperceptible, there being no concentration except in the immediate vicin- ity of the fan. If the fan be reversed and the air blown into the room it will be forced toward a given point, creating a strong draft. The problem of how to admit fresh air to take the place of that drawn away by the fan may safely be left to solve itself. No room is airtight and the weight of the air outside will force fresh air in to take the place of that which escapes. The drying room to which we referred a short time ago should be considered an essential part of every glue room equipment. This room should be divided into two parts one part for warming stock before going in to be glued up, and the other part for drying stock after it has been glued up. The importance of warm- ing stock before gluing, and of drying thoroughly after gluing and before working up, are both considered in another part of this book. While we advise dividing this room into two compartments, we do not contend that it is absolutely necessary to do so. What we do claim is that the two rooms have an advantage over the one room. Where there are two rooms, one room can be used for warming the stock for gluing without running the risk of it being affected by the moisture that is being AN IDEAL GLUE ROOM 139 thrown off by the glued-up stock ; and into the second room the glued-up stock may be run to finish off a few hours before being worked up. Both of these rooms should be well heated and ven- tilated. If the room is large it would be well to place a coil of pipes in the center as well as along the wall, as this will increase and make more uniform the circula- tion of the air ; and circulation is essential to success in CIRCULATION a drying room. The heating apparatus should have a OJ , AIR sufficient radiation to keep the temperature in the ESSENTIAL vicinity of 110 degrees Fahrenheit. Ventilators should be placed in the top to allow the vaporized moisture to escape. In a several-story building, with the glue room and drying room on the ground floor, ventilators are not always practical; in which case a fan should be installed to carry off the moist air. The foregoing are the essential features of an ideal glue room connected with a wood working plant. But the IDEAL glue room would be a building one story high, with light from above as well as from all sides. Such a room would have to stand out by itself; and while it would be "ideal" from its own viewpoint, it would be inconvenient from the viewpoint of the other departments of the factory. CHAPTER XXII. EVOLUTION OF GLUE ROOM PRACTICE. AWAY back in the early dawn of the glue and woodworking industry men were trying, as they are today, to do the work in the best and easiest way. There is very little literature extant which would throw much light on the very early meth- ods of gluing up wood work, but the contrast between A BIT OF the methods employed half a century ago and those of HISTORY the present day is sufficiently great to be startling to the old-time cabinet maker, were he to leave his Celes- tial abode for a brief visit with us who were left behind to "carry on" after he had gone. In the early days the clamping-up was done by means of a frame not unlike the screw clamp in use today; but the pressure was exerted by means of wedges driven between the clamp and the edge of the boards to be pressed together. In those days the glue was dissolved in a kettle on a stove and brushes were the only means of applying it to the wood. A wonderful step forward was made when the screw clamp was brought into existence. There mat- ters rested for some considerable time; or until the trade of "cabinet maker" became divided into several different branches. In the old days the cabinet maker took the board in the rough from the yard and carried the work along, planing, jointing and gluing, assembl- ing and finishing until the article was completed. But when the furniture and kindred industries grew to be of national importance they outgrew the old fashioned method and the one trade of cabinet making became many trades; hence it is that we have the glue room specialist of today. With the advent of the glue room specialist this department became recognized as an important branch of the woodworking industry, and some of the best mechanical brains were directed to- ward improving the method of doing the work, so as to improve the quality and lessen the cost. Then the time came when the work of the glue room 142 MODERN GLUES AND GLUE TESTING GREAT STRIDES HAVE BEEN MADE MANY PROB- LEMS REMAIN TO BE SOLVED specialist was divided and some followed after the glu- ing-up of boards; and others followed the gluing of a face veneer on these boards. From this time on things moved with startling rapidity, so much so that a detailed account would read almost like a fairy tale. It is a long step from the old hand plane and glue brush to the modern automatic glue jointer, on which the lumber is jointed, glued, clamped and cut to size in one automatic operation ; and yet it is a step that has been taken by many men yet able to do a good day's work. It is equally far from the old glue kettle sitting on a stove to the modern steam or electrically heated dis- solver with its thermometer and automatic heat con- troller to prevent overheating and spoiling, and its power agitators to facilitate solution and reduce time and labor costs; and yet many who read this have spanned the distance. Measured from the viewpoint of accomplishment, it is a wonderful stride from the old glue brush and bucket to the modern glue spreader with its rolls designed to spread heavy or light, to spread on one side or both sides of the board, as the requirements of the work in hand may demand. The same may be said of the distance between the flatirons used in rubbing on veneers in ancient days and the clamps and clumsy hand presses of a later period: or between these and the quick-acting and powerful hy- draulic presses ; and from the old rack above the stove for drying veneers preparatory to gluing to the mod- ern redryer; and yet many who will read this have lived to see it all. All these things have tended to solve the problems of the glue room ; but there are many problems belong- ing to the individual glue room that yet remain to be solved. Equipment alone cannot solve them. The same high quality brain power that brought these machines into being must guide them in their operations if they are to accomplish all they were designed to do. At one time many were of the opinion that a machine was a failure if a man lacking in mental capacity could not keep it in successful operation. But the fact that a machine, no matter how perfected, is, after all, but a EVOLUTION OF GLUE ROOM PRACTICE 143 machine, without innert animation and but reflects the intelligence of its designer and builder in operating it, is now becoming more generally recognized. That the foregoing contention is correct is borne out by the experience of European countries, as well as by the experience and observation of those who have investigated the matter here at home. It will, we think, be pretty generally admitted that the average inhabi- tant of Europe does not give evidence of that high in- tellectual development that characterizes the average American. This lack of mental development is respon- WHY THE sible for the fact that in factories in Europe which are EUROPEAN equipped with American-made machines operated by LAGS IN men working for a much smaller wage than is paid in PRODUCTION this country, the cost of production is much higher there than here. These men, though steady and consci- entious in applying themselves to their tasks, do not seem to have the combination of head-heart-and-hands so essential to the speeding-up methods in vogue here. J. B. B. Stryker, who had traveled somewhat ex- tensively through Europe prior to the war and who visited numerous factories, in writing on the subject says : "Although American-made or modeled machin- ery is so largely employed by them, the production of the average plant, comparable with ours, as to size, equipment and number of men employed falls consider- ably short of the production over here." The same may be said of the factory in this country in which the average "foreign born" is placed in charge of machines so highly developed that all they seem to require is brain-power, but which deficiency the operator is unable to supply. CHAPTER XXIII. FRICTION BETWEEN GLUE AND FINISHING DEPARTMENTS FROM time as far back as the oldest glue room man's memory goes there has been more or less friction between the glue room and the finishing department ; and we do not think a book dealing with the problems of the glue room would be quite complete were it not to make some effort to set these depart- ments right in the eyes of each other. It is not our in- SHIFTING THE tention to take sides between these departments RESPONSIBILITY further than is merely incidental to the purpose of bringing order out of chaos. The great difficulty be- tween these departments has been and now is that when defects develop in the work, each department is more interested in trying to shift the responsibility from their own to other shoulders than in trying to ascertain the real truth regarding the actual cause of the trouble. And the fact that defects in wood work are not usually discovered until some time after the goods have arrived in the finishing department and the finishing process pretty well advanced, has tended to intensify the difficulty by giving the glue room some ground for the assertion that the goods were all right when they went into the finishing room, and that some material used in the process of finishing must be re- sponsible for the trouble. The finishing department, on the other hand, when defects develop, is equally positive that the method of finishing is not in any way injurious to the glue or in any way responsible for the defects ; and declares that the defects were hidden in the woodwork before being sent to be finished; and that had the glue men done their work right no trouble would have ensued. And thus the argument proceeds ad infinitum. Take, for instance, the matter of blisters in VENEER veneered work. As a rule, these do not show them- BLISTERS selves until the goods have received at least a coat of 146 MODERN GLUES AND GLUE TESTING WATER DOES NOT LOOSEN THE VENEER TEST FOR LOOSE VENEER stain perhaps of water stain. Or the finisher may have sponged the stock with water to raise the grain, all of which furnishes the glue man with a lever with which to roll from his own door to that of the finishing department the responsibility for the trouble. But let us look at the matter calmly for a moment. Let us take a piece of veneered work about the soundness of which there can be no doubt, and let us try and remove the face veneer by soaking it with water, using a brush or sponge to apply the water. We put on one coat, two coats, three coats, six coats, and still the veneer sticks tight. Now if half a dozen applications of water will not loosen veneer when we want to remove it, is it reasonable to say that one coat of water stain or a light sponging with water caused the blisters in the finish- ing room ? Let us be honest with ourselves, even if we don't want to be with the other fellow. We will be much wiser in the end if we are. If veneer is well and truly laid, neither sponging nor one or two coats of water stain will loosen it. And if it be not well laid, or if there be any doubt about it, the best thing that one can do is to go over it with a sponge and water and by this test ascertain the facts. A usual test for blisters is to lightly tap the veneer with the finger, and if the response is a sharp "click" we know the veneer is loose. But this test is not always reliable, because the veneer may not be cemented to the core and yet be lying sufficiently close to prevent the telltale click when tapped with the finger ; and yet the very moment it is touched with water it will raise in a blister. Now why is this so ? Let us explain : The normal state for the veneer would be lying close to the core ; it was that way when it left the press, and there has been nothing done since to change this condi- tion. But when we touch the veneer with water we change the normal condition by causing the fibers to swell and the veneer to tighten and become too large for the place it is in, and it raises up to relieve the strain. But it can raise only if it is already loose from the core, because if it is firmly cemented to the core the strain thus imposed could not possibly be sufficient to FRICTION BETWEEN DEPARTMENTS 147 break the glue joint. The same thing may be illus- trated in another way: take a sheet of paper, spread it out on the table, and draw a wet sponge part way across the center, and see how quickly it wrinkles up. The moist piece at once becomes too large for the place it occupies and expands in several directions. But the paper would not have wrinkled had it been firmly cemented to a heavy body, which fact can easily be demonstrated by the simple test of trying to remove wall paper by the same process. We recall the case of a concern which had more than its share of trouble with loose veneer and open joints, without being able to ascertain the cause TROUBLE IN for some time. The glue room men and the ONE FACTORY cabinet room foreman, under whose supervision the glue room work was done, all contended that the cause of the trouble lay hidden in the dark recess of a large oil-stain vat into which the stock was dipped on reach- ing the finishing room. Things were finally brought to a head by the finisher being ordered to discontinue the use of the vat; but he demanded some proof that the vat was the cause of the trouble. No proof being forth- coming, the finisher proposed to prove that the vat was not guilty as charged, and offered to submit it to any test that might be suggested. To this end a cake of glue and two or three panels which gave evidence of being sound were put in the vat and left there for twenty- four hours. Then, at the end of that time, the glue and panels were removed, without showing any evidence of ill effects from their long immersion, the management decided that they must look elsewhere for the hidden mystery, and turned their attention to the glue room. When this was done they were not long in finding what they were after, in the shape of over-cooked glue and over-heated cauls. Having made this discovery, their troubles from this source were at an end. Men are not unlike mere material matter, in that they are prone to follow the course of least resistance, and in the case under consideration, when defects are found in glued-up work it is much easier to look for the cause in the immediate vicinity of the place where the 148 MODERN GLUES AND GLUE TESTING PLAY THE GAME SQUARE defects are first discovered and find some operation, the nature of which we do not understand, on which to lay the blame, than to make a diligent search where we are likely to find out what we are after. To be quite frank about it, it too frequently happens that neither the glue man nor the finisher is quite positive that the cause of the trouble is not in his own department, and for this reason is not very anxious to find what he is hunting for. It is a mistake for a man to remain in ignorance of even small matters merely because he lacks the moral courage to face the truth. There is no man so perfect that he never makes mistaks. Some one has said that "the man who never made a mistake never made any- thing that was worth while." And it is not the man who runs away from his mistakes or tries to hide them that succeeds the best in life. On the contrary, the man who succeeds is he who acknowledges his mistakes, grapples with them and overthrows them and uses them as stepping stones to great achievements. Let the finisher and the glue room man determine in his own heart that he will be honest with himself and honest with the other fellow. Let these two men come together with that thought uppermost in their minds when defects appear in glued-up stock ; let them together search for the cause with a determination to find it, no matter where it is to be found, and each will find that he has dropped many a headache, and many a heartache as well. CHAPTER XXIV. VENEERING SCROLL WORK. ONE of the most difficult things which the man who lays veneer finds himself up against at times is the problem of getting a good, tight glue joint on the scroll and other irregular work. To over- come this difficulty, various schemes have been tried in various places, with equally varying results. The most common practice is that of applying extra pressure in the hope that in some way the low spot where the veneer is liable to be loose will be reached and suffici- ent pressure applied to produce the desired result. There is one thing which it would be well for all of us to remember, and that is that everything has a cause, and that a repetition of the difficulty before us may be avoided by removing the cause. When we re- move the cause, the effect must cease. The whole thing FIND THE may be summed up in the maxim that "An ounce of CAUSE prevention is better than a pound of cure." In the case before us, instead of applying a sufficient amount of extra pressure to crush the article out of shape, as I have often known to be done, it would be better to start at the point of the trouble and trace back until we find the cause, or the reason why the pressure is not uniform all over. Having found it, let us remove it, no matter what it may be. Not infrequently the cause of the difficulty is in the design of the article to be veneered. It all too fre- quently happens that the designer is not a practical mechanic, in consequence of which the veneer man is often asked to do the impossible. Many times a slight change which would not materially affect the appear- DESIGNS ance of the article, nor alter the designer's conception, MUS f BE would eliminate mechanical difficulties and greatly les- PRACTICAL sen the manufacturing cost. Many designers submit their drawings to a practical man and make the sug- gested alterations. But there are a few who know so little about the things of which they are supposed to 150 MODERN GLUES AND GLUE TESTING DIFFICULTIES MUST BE ELIMINATED A LESSON FOR BEGINNERS know considerable that they feel they must guard that little with jealous care hence they resent any sugges- tions regarding the offspring of their brain. When I find one of these men I cannot help making him an ob- ject of mingled pity and contempt. Pity because he is small, and will never be any bigger. The designer who is worthy the name has nothing to fear. He is a big man in the profession. He has had his eyes open to see and his ears open to hear anything that might be sug- gested to him. But the small man he is small because he refused to open his mind to imbibe that which would have made him big. Under the most favorable condi- tions it is not an easy matter to get a first-class, de- pendable glue joint on scroll work; hence the impor- tance of eliminating everything that would make it more difficult. But even where every care has been taken by the designer to remove all unnecessary difficulties, it is not always possible for the veneer layer to produce the de- sired result, although through no fault of his own, and in consequence of something over which he has no con- trol. It is the common practice, and rightly so, to use as a caul the piece bandsawed from the scroll. Now, in order to make ourselves quite clear, let us discuss the matter before us as though we were presenting it to a class of boys in school. Let us take the scroll to be veneered and lay it on its side on the bench ; then take the piece which was cut away, and which we are to use as a caul ,and lay it beside the scroll, being careful to have the two pieces separated by the thickness of the saw which was used to cut the two apart. Having done this, we will look along the various curves and lines and we will observe that at all points the distance be- tween the two pieces is exactly the same. If we move them a little closer together we will .observe that at certain points they are nearer each other than at other points. The same thing will be seen if we move them farther apart instead of closer together. If we move the two pieces together until they meet we will see that they touch at certain points only. Now, in what we have just pointed out is to be found the reason why it VENEERING SCROLL WORK 151 is so difficult to get a good, tight glue joint between the veneer and the surface of the scroll on which it is laid ; and in the same thing is to be found a solution of the problem which the subject presents. To illustrate : Suppose we bandsaw a scroll, using a saw set to make a cut 1/20-in. in width. Having done this, we place the scroll and the caul on the bench separated by exactly 1/20-in. at any one point and we will see that they are an equal distance apart at all points. Now take a piece of veneer 1/20-in. in thickness and slip it in between the caul and the scroll, and you will find that the fit is perfect at all points. Now, suppose we remove the 1/20-in. veneer and substitute a piece 1/30-in. in thickness, and press the caul and scroll together to fill in the space resulting from the difference in the thickness of the two veneers and we will find that at certain points the veneer is tight, while at other points it is quite slack. Now, let us remove the 1/30-in. piece of veneer and fill the space with a piece 1/16-in. thick and we will find the conditions the very reverse of what they were before; the points which were tight with the 1/30-in. veneer are now slack ; and where it was formerly slack it is now tight. All this goes to show that the problem of a tight glue joint on scroll work is in the use of a veneer ex- actly the same thickness as the kerf removed by the saw. Of course, there are other things of importance to be attended to. Good judgment must be exercised in applying the pressure. Where the pressure must be applied from two directions it should be applied to the smaller surface first, otherwise it may be found diffi- cult, if not in some instances impossible, to overcome the resistance offered by the greater pressure on the larger surface to insure a tight joint at these smaller points. VENEER MUST BE THICKNESS OF SAW KERF CHAPTER XXV. LAYING FINE FACE VENEERS. THE first requisite to the successful laying of face veneer for fine cabinet work is the quality of the veneer itself. We may have a good core well crossbanded ; and we may employ the most skilled help to do the work with the best of glue ; but if the veneer is of a poor quality our work will count for naught. It is not enough that veneer be well figured to be classed as good stock ; it must be well cut, and well cared for, and well dried otherwise we are merely building trouble for the future into our work. A great deal of our best figured veneer has the fiber so badly ruptured as to make it extremely diffi- cult, if not quite impossible, to lay it with any degree of assurance that trouble will not develop; and for this reason one should exercise the utmost care in selecting the stock for fine face work. The more beautiful the figure of the wood, the more difficult it is to cut into GOOD veneer without doing damage to the fibers. The figure K is the result of the entwining and interlacing of the wood fibers in such a way that when cut into veneer many of the fibers are cut into lengths no longer than the thickness of the veneer, which may be as fine as 1/30-in., and sometimes even less. These short fibers, which run straight, or almost so from one side of the veneer to the other, make what is called "end wood ;" and unless the veneer is handled very carefully it is very liable to check at these places. It also makes it very difficult to dry without checking, as the difference in the grain is such that some parts dry out faster than others; and this uneven drying means uneven shrink- ing, and this sets up strains in the wood which certain parts are unable to withstand; and they break. For this reason, veneer, when once dry, should be kept dry, in order to reduce to a minimum the possibility of checking. But too much care cannot be exercised to insure the 154 MODERN GLUES AND GLUE TESTING A REDRYER IS NECESSARY FLATTEN OUT BUCKLED VENEER veneer being dry before laying. It would be safe to say that nine-tenths of the trouble with veneered work re- sults from the veneer not being dry at the time of lay- ing ; or, more properly speaking, at the time the press- ure is applied. We may have the veneer thoroughly dry at the time of laying on the core, and by leaving it loose so that it absorbs moisture from the glue and swells before the pressure is applied we may defeat all our efforts in drying. Where one has considerable veneering to do it will pay to put in a redryer. It is not our intention to advo- cate the claims of any one make, as all have merits worth considering; and the buyer must be guided by the work in hand and select the machine best adapted to meet his own peculiar requirements. But if one is starting in a small way, or, for instance, in a manual training school, it would not be the part of wisdom to go to the expense of installing an expensive redryer. Under such circumstances one must adopt other means to accomplish the desired result. Take boards of some soft, absorbing wood, such as basswood, and cut them in size a little larger than the veneer to be redryed. Heat these boards as hot as possible in the hot-box and lay the sheets of veneer between the boards, keeping each sheet separate, and put under pressure, applying a heavy pressure for a few moments at the start to allow the veneer to heat quickly ; then loosen the press- ure to allow the veneer to shrink, as the boards absorb the moisture, without the danger of checking. Much of the finest face veneer, such as crotch and burl walnut, is badly buckled when dry, and cannot be laid in this condition without breaking when the press- ure is applied. Stock of this kind may be moistened with water sufficiently to allow it to be flattened out with safety, then redried in the manner described above. For the benefit of any who may not know what the hot-box is spoken of above it might be well to describe the form of construction. There are many different ways of making hot-boxes ; some being made of boards, but the principle is the same in each case and we will LAYING FINE FACE VENEERS 155 describe the box which we think to be the best. It is a metal box made from sheet iron. If a large box is re- quired it is made in sections fastened together with angle-irons. The sheet-iron is made into panels, two SH EET sheets to a panel with sheet asbestos in the center. Into IRON this box steam pipe coils are placed in such a way that HOT BOX they may be used as shelves ; the number of shelves and the distance apart depending on the size of the box and the work to be done. This box is different from a drying room; the idea here being to get a maximum heat in a minimum time. For heating, either exhaust or live steam may be used. If a trap is placed at the outlet of the coils it will cost very little to heat with live steam. The stock to be heated is placed on the coils of pipe. There should be a vent at the top of the box to allow any moisture that may be present to escape ; as the boards to be heated must be absolutely devoid of moisture to do the best work. With the stock thoroughly dry it is ready to be jointed and taped if it is narrow stock. Whether ore has a taping machine in his factory should depend on the amount of work he has to do ; but one man with a taping machine can tape as much stock as half a dozen men can by hand; and as the machines are compara- tively inexpensive, it would be well to give the matter very serious consideration before deciding that you can afford to do without one. The usual method of taping veneer is to tack one piece to a board, using very fine brads for the purpose, TAPING so as not to make too large a hole, then fitting the edge VENEER of the second piece close to the edge of the first piece, being careful to match the grain and figure, and tack- ing it down in like manner. But this method has disad- vantages as it takes time to tack the veneer to the board as well as time to remove it after the taping has been done. The tack holes must also be considered, for, no matter how careful one may be, and no matter how small a brad he may use, in some veneer the mark will show. A better way to tape by hand, but one which re- 156 MODERN GLUES AND GLUE TESTING First operation: Moisten tape and run it along edge of veneer, allowing one-half to project over for the next piece Veneer reversed with gummed side of tape up ready to receive its mate The two pieces joined ready for laying FIG. 22 LAYING FINE FACE VENEERS 157 quires some skill, especially with long joints, is to place the sheet of veneer on the taping bench with the side to be taped upward (Figure 22.) Moisten the tape and run it along the edge of the veneer; one-half on the veneer and the other half projecting over. Then turn the veneer over. This brings the gummed side of the tape upward ready to receive the second piece of veneer. Speed and skill are necessary to get both j)ieces in position while the tape is sufficiently moist to take a good hold ; but with a little practice one can become most proficient. Never spread the glue on the veneer, as to do so will SPREAD THE destroy all the good effects of redrying. After the GLUE ON glue has been spread on the core it should be allowed to THE CORE set for a few minutes to become slightly "tacky." This will allow some of the moisture to penetrate the core where it will be comparatively harmless; otherwise much of it will enter the veneer before it can be gotten under pressure. And let us say to get the stock under pressure at the earliest possible moment after the veneer touches the glue in order to prevent the veneer swelling through the absorption of moisture from the glue. And in this connection let us not confuse cause and effect. In removing moisture from veneer by the pro cess known as redrying we have two objects in view. It is very seldom that veneer which has once been dried contains a sufficient amount of moisture to prove a detriment to the glue; hence the removal of the mois- ture is of secondary consideration. Moisture in veneer is a cause and not an effect. It is the cause of expan- sion in the veneer ; and it is to decrease this expansion that we remove the moisture. If the veneer is laid in to this expanded condition and becomes firmly cemented to the core it cannot shrink back to its normal width during the process of drying the built-up stock that is, it cannot draw in from the edges. The fibers them- selves will shrink, and will separate one from the other, making very fine checks in some instances; and in others larger ones. It is to prevent this that we re- move the moisture before laying the veneer when it 158 MODERN GLUES AND GLUE TESTING EXPANSION AND CONTRACTION OPEN JOINTS can shrink to a minimum width without injury to the fibers. To prevent the veneer expanding through absorb- ing moisture from the glue we advise getting the stock under pressure as soon as possible after glue and veneer come together. There are many who have the idea that so long as the veneer was made thoroughly dry before being laid all danger along this line has passed; but a more fallacious idea could scarcely be entertained. It is at this point that the real danger exists. It is seldom that a veneer which has once been dried will contain as large a percentage of moisture before being laid as will be found in a redried veneer two minutes after it has come in contact with the glue. One should not lose sight of the fact: It makes no difference how, when or where the veneer gets the moisture that expands it whether the dews of heaven descend upon it; whether it gets it from the atmos- phere during a period of high humidity or gets it from the glue just prior to going under pressure, the effect is the same expansion. And it makes no difference how, when or where this expansion was brought about, the effect is the same contraction ; and the inevitable result of the shrinking veneer after it is laid is : checks. Not a few people have trouble with butt joints opening after the veneer is laid. These openings are not always uniform ; and they do not always extend the full length of the joint. This has frequently given rise to the suggestion that the man who jointed and taped the stock was careless about his work; and has fre- quently resulted in much confusion and no little ill feel- ing. But no matter how well stock may be jointed and raped it will open in certain places if allowed to absorb moisture from the glue before it receives the pressure. Wood does not expand uniformly at all points. In the case of crotch veneer the difference in fiber and texture of the different figures allows great scope for this uneven swelling; and when those places along the edge of the joint which expand more rapidly than others, do so, and press against each other they sepa- LAYING FINE FACE VENEERS 159 rate the slower swelling parts hence the uneven, open joint. The remedy for this is the same as for checks, i. e., get the pressure on before the veneer can swell, for under heavy pressure it cannot move. THE LESSER In laying crotch veneer on ogee drawer fronts and OF TWO other shaped work some have resorted to moistening EVILS the veneer with water to prevent breaking. This is all right as far as it goes ; but it does not go far enough. Those who follow this practice admit they have plenty of trouble with the veneer checking; but they claim the checks are not as bad as would result from laying the veneer when dry ; and of two evils they are choos- ing the least. But there is no necessity for making a choice be- tween these two evils ; for both may easily be avoided. Make some forms duplicates of the forms to be ve- neered ; using basswood, or some other absorbing wood for the purpose; and heat them in the hot-box. Moisten the veneer with water to render it pliable ; and when sufficiently so bend it to shape in the duplicate forms under pressure the same as when laying the ve- neer permanently. The usual amount of moisture in veneer thus treated will make it difficult for one form to insure its complete elimination. For this reason it would be well to either re-heat the forms and make a second application, or place the veneer in the drying room for a short time. It will retain its form, so that no trouble need be anticipated from that direction. Where animal glue is used for veneer it is necessary to use warm (not hot) cauls, which help to keep the ugE glue in a liquid state for a longer period of time than WARM would otherwise be the case, enabling it to more firmly CAU LS unite with the wood. Let us lay emphasis on the im- portance of the cauls being at the right temperature. The heat in the caul helps to diffuse the moisture in the glue ; driving it into the core ; and the hotter the caul the more rapidly it drives it away. This is as it should be, for in the core the moisture can do no harm. But if the caul is not hot this rapid diffusion of the moisture creates a source of danger, as it leaves the glue in a 160 MODERN GLUES AND GLUE TESTING dry state devoid of the protection of the moisture, in which condition it is very easily injured by heat. This CAULS SHOULD can be better understood when we remember that the NOT BE h ea t required to prepare the glue for use would render it absolutely useless were it not for the protection furnished by the water which it contains. Cauls should never be made so hot that they cannot be read- ily handled with the bare hands, in which condition they can do no harm. CHAPTER XXVI. SPREADING THE GLUE ONE cannot do good work with inferior glue, but he can do very poor work with the best glue if he does not use it right. The glue-mixer may have his solution in the best possible condition, but all his care will be far nought unless those who use it afterward understand what is required of them. "The chain is no stronger than its weakest link" is a maxim no more true anywhere than here. All through the process of building glued-up stock every detail requires intelligent and careful attention, otherwise there will be a weak link in the chain of operations because of some neglected detail and the work will fall down at that particular point. The spread of glue must be uniform and of the cor- rect weight. For this reason glue-spreading machines are preferable to the old-time brush and glue pot, as the spread is evenly placed all over each piece and each GLUE SPRE AD piece is spread alike. But the operator of the mechani- MUST BE cal glue-spreader must understand the weight of EVEN spread required for the work in hand, otherwise the spread may be too heavy or too light and defective work will result. Much poor work results from a too heavy applica- tion of a heavy glue solution. It is obvious that an in- sufficient quantity of glue to the joint will result in defects sooner or later ; but not every one can see that an over-application of glue is equally bad. If one puts on an excessive amount of glue of a heavy consistency and allows it to stand until it becomes tacky there is danger of the surplus not squeezing out, and thus leav- ing an excessive amount in the joint. Where this occurs, the glue, in shrinking during the process of drying, is much more liable to break away from the veneer, allowing the latter to raise in places in the form of blisters. The modern mechanical glue-spreader has one seri- 162 MODERN GLUES AND GLUE TESTING INTELLIGENCE IS NEEDED LOOK FOR THE CAUSE OF FOAM ous defect it has no brains; but I am sometimes inclined to think that it has about as much of tnat com- modity as many men who are allowed to spread glue with a brush in some shops. Some employers appear to have the idea that the mechanical glue-spreader has brains of its own, and that a further supply is unneces- sary, and they put a man in charge of the machine who gives no evidence of being in possession of that prime necessity. From almost every viewpoint the mechanical glue- spreader is essential to the success of the veneering department ; and especially is it an economic necessity. It will do more and better work than can be done at the same cost when done by hand; and it conserves glue, which is no inconsiderable item at the present time with the prevailing high prices. More glue than is necessary is not put on the stock ; and the glue is not wasted by splashing everything around. In many plants the saving of glue through the prevention of waste alone would soon pay for the machine. In operating the mechanical glue-spreader one must give special attention to the speed, for if run too fast it will unduly agitate the glue and cause it to foam. If the glue should foam, suspend operations at once until the cause of the foaming has been ascertained. Some glue will foam much more readily than others for which there may be various causes. If the foaming continues under a reduced speed the cause will be in the glue ; the thing then to do is to examine local con- ditions to ascertain if the cause of the trouble is in the shop or came with the glue. If the glue is fresh and the dissolver was clean be- fore the glue was mixed, and the spreader was thor- oughly cleaned before it received the solution and the glue has not been overheated, then it is pretty safe to conclude that the cause is not local ; but is inherent in the glue. Some experiments have shown that glue foaming may be caused by the entire absence of grease from the glue. Good glue intended for brush work usually contains no grease, this having all been extracted dur- SPREADING THE GLUE 163 ing the process of making. When such glue is intended for the spreader, and the manufacturer knows the pur- pose for which it is intended he will usually add a suffi- cient quantity of cocoanut oil to prevent foaming. A serious case of foaming has been checked by adding a piece of beef tallow the size of a marble to each gallon of the glue solution. This amount, though sufficient to prevent foaming, would have no appreciable effect on the adhesive quality of the glue. There are other causes of foaming, but all point to GOOD WORK inferiority in quality. Cheap bone glues are prone to REQUIRES foam when used in the spreader; and glue that has GOOD QLUE been over-limed will do likewise. Such glues should not be used where good work is expected to result. CHAPTER XXVII. THE GLUE SALESMAN. SALESMANSHIP has been advanced to a science. It is no longer a wierd and mysterious magic by which one man influences another to buy from him an article which he may or may not want. It is no longer, as it was in the early ages, an exchange of necessary commodities. It is no longer a happy hunt- ing ground for the shrewd and unscrupulous, but it has THE SCIENCE evolved from its first stages of necessary exchange, OF SALES- through all the mazes of charlatanry, bringing with it MANSHIP the best from each stage, until it has grown into a sci- ence and profession. Slower than the professions of the physician and chemist in its development, it has, however, reached a degree now, in which it is building Its own etiquette and coming to its own recognition. In view of this modern science of salesmanship, I shall attempt to give my ideas of the scientific selling of glues. It is very true that there are certain lines of busi- ness in which the salesman has no competition; this, however, is the exception. There are many lines in which the competition is more imaginary than real; that is to say, the quality of the goods of the so-called competitor is so much inferior to that of the goods car- ried by a first-rate manufacturer that there is no reaJ competition. The buyer, however, who is usually shrewd, and, unfortunately is often unscrupulous, will, if possible, lead the salesman to think that competitors have given better prices or better terms, and that their goods are superior. The salesman who is not armed at every point to meet his tactics runs the risk of being imposed upon. We know absolutely that most manufacturers, job- THE CUSTOMER bers and dealers of glues desire to please the customer MUST BE and will endeavor in every way to hold up the grade PLEASED that is being bought. These men know absolutely that many buyers will try to buy glues at low prices and 166 MODERN GLUES AND GLUE TESTING SALESMEN MUST KNOW THE GAME DON'T KNOCK THE OTHER FELLOW'S GOODS some buyers may "bluff" the salesman. In most cases it has been due to the salesman's ignorance that the sale was lost. Again, nothing will destroy a buyer's confidence more quickly than to find a salesman ignor- ant of the claims made by his own house, or of the spe- cific qualities of the glues offered for sale. All sales- men need to keep themselves fresh and enthusiastic in regard to their goods, not only by frequently visiting their factories, keeping in touch with the qualities of all boilings, but also by reading all literature applica- ble to glue and glue testing. Therefore, do not super- ficially peruse the pages of this valuable book. Read all the material contained herein time and again and the writer knows absolutely that if the information is ap- plied, the salesman's success is assured. Get all the information you can from the salesmen of competing factories. Learn all you can in an open fair way, but do not resort to trickery, or to any meth- ods which you would be unwilling to have a competitor use with your house. Do not attempt to sell goods until you know absolutely that you can meet any argument and that your line of talk is of such character that there will be no doubt in the mind of the buyer that you are not a novice, not a traveling man trying to put something over, but a real glue salesman in all that the name implies. It is to be regretted that there actually are glue salesmen who seem to delight in "knocking their com- petitors." I have met men who deliberately knocked high grade glues, comparing them in quality with low grade products. A certain salesman sold hundreds of tons of grade 1^4 glue for joint purposes and claimed his glue would compare wih any joint glue regardless of price. His argument was that his glue did rot take as much water as most hide glues, but it is of the high- est quality as a joint product. Very fortunately the writer made joint determinations in the presence of the salesman and his glue was used in the test. This man has not called at my office since and he did finally say: "It takes a salesman to get by with my line of 'stuff,' but the man selling high grade glues at a reas- THE GLUE SALESMAN 167 enable or low price is not a salesman but an order taker." So many salesmen seem to suppose that business is done largely on friendship. "Friendship and business don't mix," is an old adage and a true one. You can't presume on your intimacy with a man to sell him goods; and it is seldom you can get his trade away from a successful salesman, even if you have identical grades and quote the same prices. There is no doubt that business friendship plays a very large part in business getting with all salesmen. You know how hard it often is to break in on the trade of another man, simply because he has won the friendship of his DON'T PRESUME customers. Keep this in mind, but please remember TOO MUCH ON that if your goods are right and the price reasonable, FRIENDSHIP you have nothing to fear, especially so if you merit the confidence of your trade. I have known of buyers pur- chasing glues from one factory for more than thirty years. They finally came to their senses though and now every reputable glue house known to them gets a chance at their business. To be a successful glue salesman it is absolutely es- sential to become familiar with practically all the dif- ferent lines employing glues or other adhesives in their work. For instance, in selling glues to manufacturers of wall paper it is necessary to offer only such glues as are free from foam. The glue must also be free from mucin and soaps which will not affiliate with the colors or clay. He will not offer glues to textile manufactur- ers containing mineral acids and normal sulphites since any notable proportions of these impurities will reproduce light patches on dyed wool. He is also very careful in offering glues free from coloring agents that will injure the shades of silks. He knows that pale glues have been bleached with sulphuric acid, traces, and frequently more than traces of which remain in the glue, as well as salts of sulphurous acid. When sell- ing to manufacturers of paper boxes, the salesman appreciates that either animal .or the vegetable glues may be used to good advantage. He knows that where gloss or the finish of a good covering paper has to be 168 MODERN GLUES AND GLUE TESTING MANY USES FOR GLUE THE SALESMAN SHOULD MAKE SIMPLE TESTS preserved, the animal glue has preference. When asked why he will say, because the pastes, and some gums have so much water in them that the gloss is im- paired. He also knows that the drawbacks of animal glues are higher prices and that in this respect the vegetable glues have the advantage. Mr. Glue Sales- man does not lose sight of the fact that various box factories offer different problems and every problem deserves study and well "thought out" solutions. In- deed, there is hardly an article manufactured in the making of which glue does not play a very important part in some form or other. The salesman should, if possible, be practical. Some of the things that the salesman can do along this line are trivial. Some, on the other hand, are big. The representative who can give the men in the glue room valuable tips, is always welcome and the superinten- dent or foreman may ask the purchaser of glues from time to time, "When is So and So coming? That fellow understands his business and I would like to have him assist me in solving a very perplexing glue problem." Truly, the salesman who can do these things is tying his customers to him with ropes of steel and will make his visits an event instead of a call. When visiting a propect endeavor in every way to obtain samples of the glues he is using and mail these promptly to your factory laboratories for analy- sis. The factory manager should insist upon having samples tested on the same day they arrive, or as soon thereafter as possible. In the event of a big contract being at stake and there being a likelihood of the con- tract being signed within a very few days, the sales- man should do the testing at the prospective place of business. Should this be impossible, make a few im- portant tests at the hotel. I would suggest the carry- ing of a viscosimeter, balance, litmus papers and a few beakers. The jelly can in such extreme cases be tested by what is known as the "finger test" fully explained in other pages of this book. A suitable thermometer can be carried in the vest pocket, in fact, it is as necessary for a good glue salesman to carry such an instrument THE GLUE SALESMAN 169 as it is for the physician. Stick (as you would have your glue do) until you have closed the deal. Remem- ber, you are in a sticky line so never say "quit." If you want to reach the high mark in the selling of glue, you have to have overwhelming belief in yourself and not only in the glues you sell, but in the house that manufactures them, and you must believe in yourself first of all. Extravagant hope and confidence are necessary. This is one place where extravagance is an asset. Enthusiasm is the great, far-reaching wisdom of faith it prompts and sustains the noblest efforts. If you have it you should be thankful and if you have the brand that is contagious, you are a public benefactor and a record-breaker so far as sales go. Never, Never, NEVER ! show a weakness in your argument or gen- eral sales talk, for this will be detected and like E enthusiasm, is contagious. Do not because a man buys tons of glue every year, be afraid of him and feel more at home in the small hardware store selling probably twenty-five pounds annually. Your prospects must never be approached with timidity, an "excuse-me-for- living" attitude. You are or should be just as good a man as the purchasing agent. One grave mistake I find so many salesman make, especially men representing very large glue factories, is to "jump towns" and call up over long distance tele- phone from some neighboring city and say in a seem- ingly bored way : "Went through your town this after- noon, but really it does not pay me to stop off in small cities, for you know I'm representing a very large glue 01 house and we must keep moving. Anything doing in the glue line today?" Such men are not salesmen, but may be classed as mere order takers. Of course, it may at times be necessary to resort to the telephone, but do not do so unless it is absolutely necessary and you are very well acquainted with the purchaser, knowing that he will not be offended. Don't ignore questions about competitors, and don't fail to banish from the customer's mind all doubts and prejudices, but it is a serious mistake to spend a lot of 170 MODERN GLUES AND GLUE TESTING COMPETITORS STRONG PERSONALITY time talking about competitors' glues when you ought to be sticking to the merits of your own. Answer quickly all questions, and then switch back to the excel- lence of your product. Be so enthusiastic about your own selling points that rivalry will be forgotten. In meeting competition, do not be fooled by the question of price. At present, very many lines are of practically the same quality, grades considered, and prices are about the same, so that you must bring out, as a high grade salesman should, the fact that service is the main consideration. Show what your house can do in the matter of prompt deliveries, careful packing of glues, dependability as regards uniform quality, correct weight, liberal terms, etc., and do not forget that the general reputation of your house is a selling point. The facilities which you have for keeping abreast with the times, like the employing of expert chemists and engineers in your laboratories to do your experimental and research work, thereby improving the quality of your glues all the time, is a point of serv- ice well worth consideration. Above all, a glue salesman can meet competition most effectively by a strong personality. Remember that your glues are judged by yourself, sometimes even unfairly; and remember that we are always judged by our weakest points; hence, in order to hold your trade from competitors, and to get new trade, you must possess what is commonly called "business magnetism," which is another way of saying a strong personality. A salesman called at my office a few years ago clad in a "Prince Albert" coat, very delicate kid gloves, a silk hat, highly polished patent leather shoes, a white tie, a large diamnd stud and his fingers were decorated with daimond rings. The gentleman had the appear- ance of a nobleman and when he handed me his card which stated that he represented a glue manufacturing concern, I was astonished. I noticed that it seemed to actually be impossible for the gentleman to talk because of a very high starched collar he was wearing. It occurred to me that it would be cruel to expect my THE GLUE SALESMAN 171 new acquaintance to say anything and it did seem that the subject of glue must be distasteful, so I politely informed his excellency that we are not considering new glues. I kept his card, however, and received sam- ples from time to time, but the prices were so high as to be prohibitive. It evidently cost this concern money to keep the dude on the road. Another instance was that of an apparently intelli- gent ^young man representing a prominent glue house, who came to my office in an intoxicated condition. He fairly staggered to my desk and immediately after THE "SPORT" introducing himself said to me in what was to be an undertone, that he spent the night in Toledo and had a h of a time. Did he get an order? Again, we meet the type of salesman who knows all about glues. He's the "candy salesman." No one has anything on him. He can determine glue quality by taking the lid off the barrel and smelling of the glue, or, by looking through the flake he can tell the grade. THE "EXPERT'' "Them there new glue testing methods ain't no good." Mr. Wise doesn't care what tests show, he'll tell you that it takes an expert like himself to select glues, leave it to him, he'll supply the right kind of stuff and save you money. The writer met a glue salesman a short time ago, who complained very bitterly about not being appreci- ated and the low salary his employers are paying for his services. I told him that I was sorry because he imagined his employers were trying to keep him down ; that I know the concern very well and that I did not believe them to be business men of that sort. I asked whether he ever thought of how much money he was making for his employers ? Did he make many mis- THE "CRAB" takes and get the concern into trouble because in some cases he may be overly anxious and make statements that cannot be fulfilled? Did he spend his leisure time in studying glue problems and was he familiar with the testing of glues, abuses, etc.? He thought a few minutes, then replied, "Guess you are right, have never thought of my position just that way." I hope the young man in question reads this book and especially 172 MODERN GLUES AND GLUE TESTING TRAIK YOUR SALESMEN REGARDING ADVERTISING this paragraph. He is invited to write to mo and to state whether my suggestions have proven of benefit to him, providing, of course, he has followed them. Glue manufacturers are largely to blame for select- ing some men to sell glues who are no more fitted for this vocation or profession than is the writer to drive an airplane. Indeed, of all the elements which go to make up a successful glue business, that of salesman- ship is most frequently neglected. Business is a profes- sion and a science. Salesmanship, which is a direct rep- resentation and most important factor in business, is the greatest of all professions, and is likewise a science. If some of you glue manufacturers, jobbers and dealers could watch some of the representatives I have met trying to sell glue, you would be tempted to boot them out of the office. Do not in the name of common sense regard salesmen as necessary evils. Train them and do not permit any one of them to present your cards to the trade nor announce their connection with your concern until you have every reason not to be ashamed of them. Instruct your salesmen to base their selling cam- paign on the objections that are sure to be raised. No salesman should ever start out without first having satisfactorily answered every conceivable objection from every point of view. It is singular, indeed, to observe so few advertise- ments from glue manufacturers. Some will tell you that the reason they do not advertise is because they employ salesmen whose business it is to call on pros- pectives and customers, show samples of glues and discuss their merits. The glue manufacturer seems to forget that through the advertisement published in good, live trade journals he will reach thousands of glue users at nearly the same time and the salesman can call on but one person at a time. It is, of course, true that the advertisement may not always complete a sale, but it will certainly pave the way for future busi- ness, for it will impress the name or an attractive qual- ity so that the reader will think of your concern when in the market for glues. A good ad will invariably influence the reader in favor of your commodity. THE GLUE SALESMAN 173 The writer has heard glue makers say: "Why should I advertise? Supposing I list grades of glues based on Peter Cooper standards; I name prices and some competitor will answer my ad stating that he is prepared to offer lower prices. He will not fur- nish the same grades, but too few glue users test glues and would be unable to tell the difference, so I lose out because of being honest and the trickster gets the busi- ness." The writer must admit that this has been true, but we must also remember that we are all doing busi- ness differently than we did five or ten years ago. Where such a condition exists it is the best kind of ad- vertising to show up the cheater and by so doing the glue buyer will be your friend for life. Many glue manufacturers are doing a great deal of effective advertising by means of form letters, which are printed in imitation of typewriting. Indeed, some of the very best form letters I have ever perused were written by some genius who certainly understood the requirements of glue users and his letters without a FORM doubt "brought home the bacon." At the present time LETTERS printing offices in nearly all of the large cities can fur- nish form letters from typewriter type that are good imitations of typewriting. Good matching is very im- portant in inserting names, addresses, and other mat- ter in form letters. Glue advertisers can sometimes afford to distribute novelties that will keep their names before the public. I often wondered why manufacturers do not prepare printed tables for the glue buyer showing viscosity test, jelly, etc. It would certainly be splendid to pre- pare tables from different strength solutions run through various viscosimeters, especially the viscosi- meter having various sized apertures. Again, inex- pensive thermometers for the glue room would be appreciated. These novelties would likely not bring direct sales, but would support other advertisements together with the work done by your salesmen. Your novelty should be a constant reminder of your business and should be of such value so it will not be destroyed. CHAPTER XXVIII. BUYING AND SELLING GLUE. THE functions of every purchasing department in a manufacturing establishment are: First To secure the most satisfactory material required in the manufacturing processes. Second To secure the DUTIES OF most desirable delivery of the material, keeping com- PURCHASING plete and accurate record of all unfilled purchase DEPARTMENT orders. Third To obtain the best terms of payment and the lowest prices, quality considered. Fourth To record and classify materials and sup- plies used and purchases made. Fifth The buyer should have complete lists of all manufacturers of glues and other adhesives. He should keep in touch with these concerns and though he can- not buy from all, and, would possibly buy but from one or two, nevertheless, it is well to receive quotations and sSamples for comparison. The successful accomplishment of the first function demands that the glue buyer shall be a man who has a working knowledge of the particular industry for which he is buying this class of material. If he has in addition acquired the knowledge of glue testing, so much the better, for he will be able to make practical application of such knowledge. If care is exercised to obtain a man of the qualifica- tions indicated to purchase glue, there will be far less liability to make the error so frequently made, of buy- ing grades of glues good enough in themselves, but not exactly adapted to the particular purpose for which the glue is desired. The second function applies largely to the traffic department, or, in small plants proper routing should be specified by the glue buyer. Again, it is usually im- portant to ascertain at the time of purchasing the age of the glue and the possible date of shipment. To obtain the lowest price does not mean "cheap 176 MODERN GLUES AND GLUE TESTING SUBSTITUTING PRICE FOR QUALITY TRAY CARDS glue." It is to be regretted that in too many cases glue is considered as just glue. Some salesmen fear compe- tition and have no desire to enlighten the glue buyer as to glue standardizing. The tendency, therefore, is for the salesman to say that his glue is as good or stronger than the one the buyer is using, that it takes more water and as a natural consequence is a cheaper prod- uct so far as glue economy is concerned. The salesman may make price the predominating element, to substi- tute salesmanship for science. High grade glue costs money and no manufacturer can afford to sell an article for fifty cents that possibly costs him one dollar to produce in his factory. Nevertheless, prices may be unreasonably higher and the buyer should possess the ability to determine the lowest just and fair price, the quality of the material considered. It is well to list manufacturers, jobbers and dealers selling glue on suitable tray cards. The card should give the name of the manufacturer, jobber or dealer, address, grades of glues manufactured, financial rating (the financial rating being a fairly good barometer to show whether or not the manufacturer, jobber or dealer is financially able to carry out the terms of the crder of contract.) The card should also show the kind of glue manufactured, hide, bone, vegetable, water- proof or any other adhesive. The buyer should ascer- tain, if possible, what grades of glues the manufac- turer, jobber or dealer specializes in. The manufac- turer of paper boxes would likely not be interested in high grade hide glues and the wood worker would not find the box-maker's glue practical in his line of work, therefore, it would not be advisable to list all grades of glues and the manufacturers, jobbers or dealers handl- ing the grades and kind of glues you do not require. The back of this card may be arranged in columns for the purpose of entering quotations. The first col- umn would show the date, the second manufacturer's or jobber's number of the glue boiling; the third, grade of glue; fourth, the number of unsold pounds in the boiling; fifth, F. 0. B. point; sixth, price; seventh, terms. Ordered columns may also be provided on the BUYING AND SELLING GLUE 177 back side of the card. First column showing the date and second, quantity ordered. The glue buyer must insist upon receiving timely requisitions from all the departments requiring glue. Under ordinary circumstances the purchaser of glues RE Q U J SITIONS should place no orders until he has first received a REQUn requisition from either the stores department or the department that requires material. A positive rule should be laid down that all glue requirements be anticipated in ample time so that the buyer will not be compelled to purchase unsatisfactory stock from possibly a nearby dealer so as to avoid a "shut-down." Again, requisitions should be signed or countersigned by either the foreman requiring the ma- terial or the superintendent. Requisitions can, of course, be drafted to meet individual requirements. When contracts are made involving a large invest- ment, considerable testing and investigating will be necessary and the writer's experience has been that it will require from thirty to sixty days to get samples, test them, receive quotations and finally decide upon the glue that will be contracted for. . Departments requiring glue or store rooms should carry what may be termed a "Low Stock Report." The glue should be given a low limit and when this is reached the workmen, foreman, stores-keeper or who- ever has charge of the glue should report promptly to the person issuing the requisitions. It is also imperative to keep a complete record of all tests and to file them for future reference. A vertical two-drawer bill file cabinet answers this purpose very nicely. In the top drawer file favorable reports. In the second drawer the unfavorable. The advantage of this KEEP A scheme is apparent, for it is a simple matter to deter- RECORD or mine within a few moments who supplied the best and TESTS who the poorest samples. All test cards, good or poor, should be filed. I have found this scheme especially valuable in calling the bluffs of glue salesmen who per- sist in knocking their competitors' glues. The manufacturer spending money in the way of the salesman's salary, railroad and hotel expenses de- 178 MODERN GLUES AND GLUE TESTING GIVE THE SALESMAN A CHANCE serves consideration. It is to be regretted that many glue buyers do not appreciate this and in many cases glue salesmen representing the most successful and reliable glue houses are turned down not even given an audience. When a salesman spends time and money to visit you, he has something to say and if you are a good buyer you will permit him to have his say. To be sure there are many men who suppose the buyer has no other duties than to listen to stories, smoke cigars, and be a good fellow. The writer usually allowed every salesman from five to ten minutes and he was given to understand when entered my office that he must be brief. Another suggestion: Whenever you find a boiling that is highly satisfactory, buy the entire boiling. Of course, the writer appreciates that small manufactur- ing plants cannot at all times avail themselves of such offerings, however, the glue manufacturer may reserve a certain quantity or possibly all of the boiling for the small manufacturer, especially so if a reasonable de- posit is made or a liberal amount taken in on the first shipment. When buying the entire boiling you know absolutely just what you are receiving. The writer has never regretted doing this. If the buyer of glues will avail himself of the infor- mation given he will avoid excessive buying, inferior quality, high prices and poor deliveries. Right buying means an improvement in the quality of the goods, increased production, and, last but by no means least, satisfied customers. CHAPTER XXIX. PAPER BOX ADHESIVES. THE average paper box manufacturer buys very cheap glue. This is usually a bone product of the lowest grade. It is possible to use almost any kind of glue in the manufacture of paper boxes and the real factor is the price. It is, of course, imperative to select glues that are not in the stages of decomposition and the tests explained in this book, when properly applied, are all the information that is required to determine this point. Again, in boxes that are printed m i i .. -i -i i-ii br*L,LCTlO,N OF or colored it is necessary to avoid glues that are too GLUE FQR strongly alkali or acid. The litmus tests explained for PAP acidity or alkalinity must be applied. If the paper box maker will study all the information explained in the pages of this treatise he will eliminate all of his glue troubles. It will be appreciated that it takes but little glue room abuse to almost destroy the adhesiveness of a cheap or low grade glue. Watch the temperature. When heated, all glues are gradually killed and the damaging action begins as soon as the temperature of the solution reaches 120 degrees. Unfortunately a slightly higher temperature than the temperature at which damage to glue begins is quite necessary, never- theless, common sense must enter into the problem and if the paper box makers will exercise great care they can obtain a higher degree of efficiency and in many cases greatly improve the quality of their product. The novice will be surprised to observe the possi- bilities of box making machines. There are a number of popular machines ; we will, however, discuss the B0 x MAKING merits of but three. MACHINES The Jagenbry Box Making Machine automatically feeds the cut out blanks, forms the box, glues, applies, cuts strip paper and turns striper in and over. The Staude Automatic Folding Box Gluer will auto- matically feed blanks one at a time at a high speed, 180 MODERN GLUES AND GLUE TESTING ESSENTIAL REQUIREMENTS SILICATE OF SODA glue, fold, count and stack in a vertical pile that keeps the glued seam under pressure so it cannot pop open. There is a possibility of combining vegetable and mineral adhesives such as starch solutions and flour pastes and silicate of soda. The essential requirements would here be that the vegetable part should not con- tain any considerable excess of free alkali. Most box makers have their own private formulas. One of the points to remember when working out a formula for a paper box adhesive is the setting of the glue. Of course, we know that the lower the tempera- ture in the work-room the lower the temperature of the warm liquid glue, and the higher the grade of the glue, the quicker will the glue set. For the building of chip or container board silicate of soda is used. The stock is built up the same as ply- wood. The only pressure applied, however, is on the machine when the stock goes through the squeeze rolls. Silicate of soda has much less water in it than is used with other adhesives and the various grades are pro- duced with considerable latitude in setting. It requires from fifteen to twenty pounds of silicate to build up 1,000 square feet of three-ply board, 15 pounds as minimum and 20 pounds as maximum. It varies between these two points on different grades of paper. Each additional ply will require from 71/2 to 10 pounds additional silicate of soda. A three-ply board has two pasted sides. A four-ply board has three pasted sides, each side requiring 7 l /9 to 10 pounds of silicate of soda per 1,000 square feet irrespective of caliper of the board. Silicate of soda is packed in either wooden barrels or metal drums, both containing approximately 600 Ibs. The barrels have two openings, one in the center and one in the head, and the silicate can be drawn from the same with a good sized spigot, say one inch inside opening. The user should always draw from the barrel in a small container the desired amount for one day's use, and when the brush is not in use the bristles should be submerged in water, which will preserve them. CHAPTER XXX. AVOID ABUSES. EVERY office and department in any manufactur- ing plant requires system and organization. When these important factors are neglected the quality of the goods is certainly compelled to suffer and the manufacturer usually realizes a loss instead of a gain. No manufacturer is in business for his health. He cannot "break even" year after year and he is either making or losing money. The woodworking manufacturer knows that it costs money to repair open joints or blistered and loose veneers. It isn't always the fault of the glue, as has been generally charged, and I know from experience that in most cases the workmen or the system are at fault. Our first duty is to select the grade or grades of glue that will give reliable results. When selecting glue for wood work we must insist upon receiving the purest glue avail- able, glue that is not loaded with chemicals to give fictitious value. The writer has already explained the requirements of various lines and we will not here repeat anything that has been stated. It is immaterial whether we manufacture matches, emery wheels, cloth, paper boxes, furniture, caskets, pianos, etc. We are all interested in glue that holds. It is an absolute fact though that different workmen may get different results with the same glue all made in one boiling at the glue factory. Why such differences ? The answer is simply, that every one of the men may abuse the glue, one more than the other and when used the quality is not the same high grade as when originally dropped in the glue cooker. The one feature that is an absolute essential to the proper working or handling of glue is intelligence. We want to forget that any Tom, Dick or Harry can pre- pare glues, and all you need give him is a few pails, a quantity of glue and show him where the faucet is so that he can prepare the glue for "soaking." We must RESULTS 182 MODERN GLUES AND GLUE TESTING LET YOUR MEN READ THE BOOK GLUE ROOM TEMPERATURE train our men, and to do so every manufacturer, large or small, can well afford to place our glue books in the various departments so that the workmen can learn how glue should be prepared and properly handled to get 100% efficiency. The workmen who master all this book contains may rightly call themselves experts, and if this is done the manufacturer will then have the assurance that glue room troubles are a thing of the past. I did not incorporated this statement to boost the sale of the book, but this is absolute truth and the writer has in mind only the welfare of his readers. Practically every department in a manufacturing plant has one or more foremen. These men are singled cut to oversee the work. This should also be done in the glue room. Single out the most intelligent man you have in that department and hold him responsible. This need not be the foremen for the reason that these men have too many details and they likely cannot give the preparation, distribution and using of the glues the close and careful attention so necessary if quality is to be realized. Proper equipment is very necessary. We are going to discuss equipment in another chapter so will next direct your attention to the temperature of the glue room. We all know how imperative it is to have a fairly uniform temperature in varnish rooms. Your glue room is just as important. Again, you avoid draft in the varnish room and we must do so in the glue room. Chilled glue will cause trouble and when the stock is too hot, owing to a very high temperature in the gluing department, the men are uncomfortable. Some men insist upon heating the wood until so hot that one cannot touch the heated surface with the naked hand. When wood is heated hot, too much glue is taken up. Then when the wood cools off the air in the pores beneath the glue contracts as it cools, creat- ing a suction which draws the glue farther into the wood, and this is liable to seriously affect the joint for there may be a little glue left on the surface, as it is all absorbed by the wood. Having the ideal glue room conditions and the most AVOID ABUSES 183 suited stock for our peculiar requirements, we must measure the glue and water. Hundreds of manufac- turers in all lines of business neglect doing this and the men pour water on the dry glue until the surface has GLUE AND been covered. Weigh your water as well as the glue W ATERMUST and watch the proportions very carefully. BE WEIGHED The function of soaking is to get back into the glue the liquid it originally contained. Precautions must be observed that will insure uniform softening prior to melting. Very frequently one finds long or wide flakes. It is well to break them into suitable sizes prior to soaking. Do not permit pieces to stick out of the water. All of the glue must soak and unless this is the case it will take a considerably longer time to melt than if soaked properly before applying heat. Many so-called "glue experts" object to soaking the glue over night. This is perfectly right in the case of flake glues, providing, of course, the room is not too hot. Hot summer nights are not very desirable. Glues should not be soaked too long as too much soaking kills the strength. Thin cut, high-test glues absorb water rapidly. They will therefore soak in a much shorter time than thick glues. This applies as well to ground glues. A very good plan is to pour water (taken from the quantity weighed) into the soaking container so that when adding the glue it will surely become soaked. Unless this is done you are taking chances and there may be particles or flakes at the bottom that will not become saturated. Stir again and again. This will assist very much and will to some extent shorten the time of the soaking. Use only pure, cold water. Some men seem to be under the impression that there is no better water than that which has been chemically treated in the boiler for the prevention of scale. The writer at one time visited a woodworking plant having consider- DO NOT USE able trouble with glue. The grade was splendid, the BOILER men did not appear to overheat it and the entire prob- WATER lem had me guessing until I saw a workman coming up the stairs with two pails of water. I immediately be- came suspicious, and asked him for what purpose he 184 MODERN GLUES AND GLUE TESTING CORRECT HEAT GLUE ROOM EQUIPMENT intended the water. He replied, to soak the glue. I said, "Haven't you water faucets in your glue room?" He replied, "The clearest water we can possibly get is water that has been softened and this comes from the boiler." Here was the answer. Again, I observed men drawing water from the water jacket in the glue cooker. This sort of thing is inexcusable and should not be tolerated in any glue room. We have perused hundreds of articles in trade papers dealing with the subject of overheating glues. Every salesman cautions us against this evil. We feel, therefore, that little information is necessary along this line. However, for the benefit of any reader who may not know what damaging effects heat has on glue, I want to state that the most desirable temperature to heat glue is approximately 148 degrees F. For some classes of work from 138 up to 145 is perfectly safe. The moment a mixture of glue and water is heated enough to melt it a gradual change begins to take place in such a way that the water-taking or spreading capa- city of the glue is gradually destroyed. It is caused by the water attacking the glue and heat increasing the effect of the attack. Heat should be applied indirectly. That is, do not permit steam to come in direct contact with the glue. Open iron kettles should never be employed. Of course, there is always more or less evaporation in glues. How- ever, if the cookers or glue pots are closed this evapo- ration would, to a great extent, be eliminated. The con- struction of the glue cookers, pots, tanks, etc., is there- fore of great importance. Our grandfathers would work with open iron kettles. Shavings, sawdust and foreign matter would be conspicuous in the glue pots. Therefore, they found it necessary to add more dowels or drive more nails to assist the glue in holding than is necessary today. We could, of course, go into details regarding cookers. However, there are a number of very good dissolvers or commonly called "glue cook- ers," on the market and every manufacturer makes certain claims for his product. The writer suggests AVOID ABUSES 185 though that the buyer be very careful and that he buy only such glue room equipment as will give lasting results. The equipment being right, there should be no trouble upon obtaining a uniform melt at the minimum temperature. You would not think of operating your boilers without water and steam gauges. Therefore, it is im- perative that you provide thermometers to your cook- ers, glue pots and glue spreaders. The automatic tem- perature controller is a wonderful appliance and by its use the supply of heat is automatically regulated. When melting do so slowly. Every experienced glue user knows that there is nothing to be gained by at- tempting to dissolve the glue within a few minutes and MELT QLUE that when this is attempted a scum is formed over the SLOWLY glue, preventing its proper melting. It is well to prepare two or three batches a day or more if necessary. Do not prepare so great a quantity that enough glue is dissolved to last three or four days. A glue solution when allowed to cool and then is re- melted has not the same tenacity as a freshly prepared solution. Consequently, for ordinary work, the quan- tity of glue solution prepared should not be more than is required for immediate use. The melting pots should be kept perfectly clean. Much unnecessary waste may be avoided through ob- servance of cleanliness. After the melted glue becomes sour, and, unless this sour glue has been removed from the melting pot it will spoil the fresh solution. Do not, therefore, tolerate dirty pots and do not, under any circumstances, mix or permit a mixture of old dis- solved and new glue. Again, do not permit glue to freeze. If glue jelly is frozen through it will crumble and act about like over- ^ NOT ALLOW heated glue. Do not use the glue until it has thoroughly melted. So many glue users seem to labor under the impression that partly dissolved glue can be used with perfect safety. This is wrong and should not be put into practice. 186 MODERN GLUES AND GLUE TESTING Do not permit the temperature of the glue to raise or lower. Keep it uniform. Store glue in a dry place and do not unhead the barrels until you are ready to use the glue. Co-operation is absolutely necessary in every line of business, and in every department. Your men will be glad to co-operate if given a chance. Having per- fected your organization so that you know absolutely that you are receiving 100% glue room efficiency, do not forget the men who are assisting you in making this possible, and, the men who are actually doing the CO-OPERATE work. When yoyr men are doing good work, be big WITH YOUR enough to go to them and tell them so. This requires a MEN little giving on the part of the employer, superinten- dent or foreman, but it is no expense it is merely the giving of credit where it is due. As your men improve in your service their incomes should improve. The pay envelope and the occasional word of commendation are powerful tools that you have at your command for a persistent sequence of growth toward a better business. MODERN GLUES AND GLUE TESTING 187 MEMORANDA 188 MODERN GLUES AND GLUE TESTING MEMORANDA MODERN GLUES AND GLUE TESTING 189 MEMORANDA 190 MODERN GLUES AND GLUE TESTING MEMORANDA MODERN GLUES AND GLUE TESTING 191 MEMORANDA 192 MODERN GLUES AND GLUE TESTING MEMORANDA University of California SOUTHERN REGIONAL LIBRARY FACILITY 405 Hilgard Avenue, Los Angeles, CA 90024-1388 Return this material to the library from which it was borrowed. RECEIVED OCT 2 7 1997 EL/EMS LIBRARY M lif APR 2 2005 SRLF 2 WEEK LO X mm