Odor and Keeping Qualities 
A 50 cc » portion of the glue solution used in previous tests 
shall "be placed in an uncovered container and held in an incubator at 
37°-38° C. for US hours. At the end of this time it shall he free from 
any odor of decomposition. 
Grease, Ash, and Other Miscellaneous Materials 
If for any reason it seems desirable, tests may also he made 
for ash and grease content and the presence of materials that give a 
fictitious value to a glue. The presence of more than U percent ash in 
clear glues and 10 percent in opaque (white) glues, or 1 percent of grease 
(determined "by the Kissling or other satisfactory extraction method that 
shows total grease), or the presence of materials which increase the 
viscosity or jelly strength may he cause for rejection. 
Wood-Joint Tests 
Wood-joint tests are not a part of the federal specification. 
They are not suitable for the grading of animal glues "because more direct 
and accurate evidence of the physical properties of the glue is afforded 
hy the viscosity and jelly strength tests. Strong joints may be made with 
a number of grades of animal glue but different gluing conditions must be 
used according to the grade of the glue. If wood- joint tests are made 
with glues of different grades under a uniform set of gluing conditions, 
the grade of glue that gives the best results is the one best adapted to 
the particular gluing conditions used and the results are not an accurate 
measure of the inherent strengths of the grades tested (12). 
Wood-joint tests are, however, of decided value in determining 
the combination of gluing conditions that should be used with any given 
grade of glue. The Forest Products Laboratory has adopted the following 
procedure for making the wood- joint test (ll_): Selected pieces of v:ood, 
usually sugar maple, are stored in an atmosphere at 30 percent relative 
humidity until they have reached an equilibrium moisture content with this 
condition. Matched pieces, approximately 3A" x 2.5" x 12", are carefully 
surfaced to insure smooth, plane, and parallel surfaces. The pieces are 
glued under controlled conditions of temperature, amount of glue spread, 
duration of assembly period, and amount of pressure applied. They are 
allowed to remain under pressure over night and then returned to 30 percent 
relative humidity for seasoning. A seasoning period of at least a week is 
allowed between gluing and testing. The glued pieces are then cut into 
specimens and tested in shear. The unit pressure required to break the 
joint and the amount of wood fiber torn in breaking are measures of the 
quality of the joint. The effect of gluing conditions on joint strength 
is discussed in detail in U. S. Department of Agriculture Bulletin 1500 (11). 
RU92 
