10 BULLETIN 15 0, U. S. DEPARTMENT OE AGBICULTUEE 
The grade of an animal glue is generally determined by the com- 
bined results of jelly strength and viscosity. 11 Other tests, such 
as for grease, foam, odor, and acidity or alkalinity, are of less 
importance, but nevertheless significant for animal glues used in 
woodworking. 12 Mechanical tests of specimens of dried glue or 
glue coated or impregnated material have been used to some extent 
(4, 6, 23, 28, 34), but their value is questionable as a means for 
determining the suitability of a glue for woodworking. Wood- joint 
tests, although commonly made, are also not a reliable means of 
judging the grade of an animal glue. Unfortunately, joint tests 
are the only tests yet available for determining the suitableness of 
blood-albumin, casein, vegetable-protein, and starch glues for use 
in woodworking. 
A description of the principal methods and apparatus used for 
testing glues is given in the appendix. 
PREPARATION OF GLUES FOR USE 
A standard procedure should be adopted in preparing glues for 
use. This involves such details as the amount of water to be added, 
method of combining glue and water, and time of mixing. A stan- 
dard procedure gives a more uniform mixture and avoids too much 
reliance on the individuals who do the mixing. Clean, cold water 
should be used with all glues. The quantity of dry materials and 
water should be accurately determined by .weight. The correct 
proportions of glue and water vary for different kinds of glues, 
woods, types of joints, and conditions under which the gluing is 
done. (See pp. 11, 12, and 13.) For most glues used in wood- 
working the proper amount of water varies from iy 2 to 3 parts 
to 1 part of dry glue by weight. With a given glue the amount of 
water used should be less where quick setting is desired. The amount 
of water used should also be less with porous woods, end-grain 
surfaces (p. 42 and Table 7), or where high joint strength is desired, 
than with nonporous woods, side-grain surfaces, or where high 
strength is not required. A glue mixture with a large proportion of 
water gives a large spread and is in a satisfactory condition for 
pressing a long time after the spreading. "The mixing should be 
done in such a way as to produce a solution of uniform consistency 
relatively free from air bubbles and particles of undissolved material. 
PREPARING ANIMAL GLUES 
In preparing animal glue the grade largely determines the quantity 
of water to be added. A glue grading No. 12 in the National Asso- 
ciation of Glue Manufacturers scale (p. 15) requires about 2*4 parts 
of water to 1 part of dry glue by weight for high-quality joint 
work and about 3 parts of water to 1 part of dry glue for veneer 
11 Domestic glues are commonly graded upon both jelly strength and viscosity, but 
imported glues may be graded on other bases. According to Bogue (6'), " In Germany the 
viscosity test proposed by Fels, made by the use of the Engler viscosimeter at 35° €., 
seems to be in greatest favor. In Italy a combination of viscosity and melting point is 
used. In France and England the viscosity test and the melting-point test by Cambon's 
fusiometer are employed." 
12 Definite specifications covering these tests are given by the Federal Specification Board, 
Washington, D. C, for an animal glue suitable for high-grade wood-joint work. 
