HARDWOOD RECORD 



29 



projection at both ends of each segment which extends along the 

 side of the next segment above and below (Fig. 1). Vessels are invari- 

 ably filled with dark-brown masses called tyloses. 



The walls of the vessels have bordered pits (Fig. 1, 6. p.), especially 

 on the sides adjoining other vessels. These pits are usually arranged 

 in horizontal rows on the radial surface of vessels in contact with pith- 

 ray cells. True tracheids are found sparingly in this wood, and are 

 then only in contact with vessels of the earlywood. 



Wood fibers (Plate IV, w.f.) vary in length from .630 to 1.433 milli- 

 meters in length, with an average of 1.047 millimeters (Table II). 

 They are often less than .02 millimeter in diameter and are long- 

 aeuminate at both ends. These elements are usually arranged in radial 

 rows and have moderately thick walls, the cell cavities being large in the 

 earlywood and almost entirely obscured in the outer portion of the late- 

 wood. Wood fibers are usually flattened radially in the region of large 

 vessels, because of the pressure exerted by the rapid grovrth of the 

 latter. The pits on the radial walls of wood fibers are simple, minute, 

 and arranged in a single row. 



Wood-parenchyma fibers (Plate IV, w.p.f.) are usually scattered 

 throughout the annual layer of wood, but they are not infrequently 

 arranged in tangential bands in the latewood. In the earlywood these 



fibers are chiefly in contact with vessels, where they are usually com- 

 pressed either radially or tangentially ; elsewliere, wood-parenchyma 

 fibers are circular or polygonal, with considerably larger cell cavities 

 than the ordinary wood fibers. They are also somewhat shorter (Fig. 3) 

 than wood fibers and are composed of from three to eight, but more 

 frequently three to five, wood-parenchyma cells, which have horizontal 

 or sometimes oblique partition walls. The radial and terminal waUs 

 are marked by numerous simple pits. Crystals of calcium oxalate 

 (Fig. 4) are seldom present, except in the wood-parenchyma fibers bor- 

 dering pith rays. These polygonal crystals occur in vertical rows vary- 

 ing in number from a few to eight or ten. 



Pith rays (Plate IV, p.r.) are regularly distributed throughout the 

 wood. They are from one to six, but chiefly from three to five, cells 

 wide, and from a few to twenty-five cells high, spindle-shaped and 

 elongated-elliptical in outline. The cells of the pith rays are elongated 

 in a radial direction, and are usually from one to four times as long as 

 wide. The cells in the upper and lower rows (marginal cells) (Fig. 7, 

 m.r.c.) are shorter in the radial direction of the wood fibers. The 

 walls of these marginal cells are usually somewhat thinner and contain 

 less numerous pits than the inner cells, especially on the radial walls. 

 Crystals of calcium oxalate are rarely present in the pith ray cells. 



W■^TOtfac>5 g >k\:a^X)^o;TOTOTOTOTO^^^ 



The Glue Side of Veneering 



When "we consider that without glue there would never have been 

 any veneering industry we can realize something of the importance 

 of glue in the business of veneering. The term glue is meant to cover 

 all of the cementing substances used for fastening wood together. 

 Though glues were discovered and used in the early days of civiliza- 

 tion and have always been a factor in joinery, yet not much im- 

 portance was given this phase of the business until the built-up ply 

 wood came into use. It was this which led to consideration and closer 

 study of the glue side <of the business. 



In the earlier days of the work glue was looked upon as a mys- 

 terious foreign substance that the wood worker was not supposed 

 to know much about except that when heated and melted and 

 applied to wood it would hold it together. When the veneer industry 

 had developed to the point of using enormous quantities, however, the 

 cost of this item was such a factor that it led to a search for moans 

 of reducing it. The matter of quality came in about that time. It 

 was found that sometimes glue failed to perform its duty and work 

 went bad. Sometimes this was because of unwise efliorts to save cost 

 either through the use of too small a quantity or from buying an 

 inferior glue or making up an improper mixture. Anyway, investiga- 

 tion of the subject soon showed two factors to consider — the factor 

 of cost, and the factor of safety or quality. 



Up to this stage of the development no one but the glue people 

 seem to have made a careful analytical study of glue. It is doubtful 

 if even the glue people had concentrated enough attention on the 

 matter of careful and thorough analysis. However tha* may be, the 

 ■veneer industry eventually created quite a stir in the matter of 

 gluing. Important users made careful studies of the glue used. 

 This developed appliances as well as formulas for testing and grading 

 and heating glues. 



One of the great discoveries of this period was that many people 

 had been injuring the quality of their glue by overheating it. Experi- 

 ments showed that glue could be cooked and damaged even when 

 enclosed in a water-jacketed vessel. The experimenters soon sounded 

 a warning against excessive temperature in preparing glue. The 

 first ones brought it down somewhat from the original cooking tem- 

 perature, and by and by these were scaled down still lower until 

 finally there was a pretty general agreement among authorities on 

 the subject that the temperature in the preparation of glue should be 

 kept somewhere between 140 and 150 degrees F. 



It was discovered, also, that freshness was a quality; that glue 

 kept heated and mixed with water deteriorates rapidly La value, con- 



sequently to get the right results everything should be cleaned up at 

 the end of the day and only fresh stock used in glue work. 



During all this time there was a more or less persistent casting 

 about for other substances than the standard glue product to use 

 in cementing wood together. The first outcome was the use of casein, 

 which was taken up extensively but retired after a season or two 

 —just why is not clear. Some say it was worth more for other pur- 

 poses, others that it was uncertain. Sometimes it would give excel- 

 lent results but at other times it would fail, and this uncertainty 

 caused it to lose favor. 



The casein product closely resembled in appearance and was used 

 in practically the same manner as the regular glue, but with the 

 passing of casein there came other products with their own peculiar 

 methods of preparation and application, differing in some instances 

 from that of standard glue. The most important of these, the one 

 receiving pretty wide attention at the present time, is a product 

 known as a vegetable glue. One of the noticeable differences between 

 this and standard glue and its use is in that the vegetable glue can 

 be and is commonly used cold. 



This vegetable glue product has become important in veneering 

 and is today probably the most formidable competitor of the old 

 standard glue. Among the other glues are silicate of soda and some 

 special formulas of secret compositions that seem to bear relation to 

 what is known as the Eussian idea in veneer work. 



Silicate of soda or water glass is dissolved by heat, and when 

 reduced to liquid may be kept for some time and applied cold. It 

 is used as a i^rincipal base into which other iagredients enter in 

 varying proportions to make up the glue mixture. There are some 

 branches of the built-up lumber industry into which this product 

 enters quite extensively — that of making two and three ply stock for 

 packing boxes and some plain panel work. It does not seem to have 

 found favor in the furniture trade or in fine cabinet work. Just 

 why, it is a little difficult to understand. Those who have made a 

 study of it simply pass the subject by with saying that it serves very 

 well for certain purposes in making cheap built-up lumber and is a 

 comparatively inexpensive glue, but does not find favor in the finer 

 grades of work. 



What is known as the Bussian method was explained at a recent 

 meeting of veneer and panel manufacturers, but the explanation had 

 to do more with the handling and the time of using the veneer and 

 the qualities of the built-up product than with the nature of the 

 composition constituting the glue. It seems that the practice in Rus- 



