62 BULLETIN 15 00, U. S. DEPARTMENT OF AGRICULTURE 
APPENDIX 
GLUE FORMULAS 
The following glue formulas, with directions for mixing, were developed at 
the Forest Products Laboratory by the laboratory personnel and are available 
for the free use of the people of the United States. 
CASEIN GLUE FORMULA NO. II 33 
Ingredients 
Parts by weight 
Casein 100 
Water 220 to 230 
Hydrated lime 20 to 30 
Water 100 
Silicate of soda 70 
Copper chloride 2 to 3 
Water 30 to 50 
The 220 to 230 parts of water added to the casein is approximately the right 
amount to use with Argentine (naturally soured) casein; but if a different 
casein is used the water requirement will lie somewhere between 150 and 250 
parts by weight. The correct amount for different caseins must be determined 
by trial. 
The formula presupposes that a high calcium lime will be used. A lime of 
lower grade may be used, but a proportionately larger amount of it will be 
needed, or the water resistance of the glue will be sacrificed. It is suggested 
that for the first trial the user try 25 parts of lime. If this does not give good 
results the amount can be varied within the limits specified. 
The density of the silicate of soda used should be about 40° Baume, with a 
silica-soda ratio of from 3 to 3.25. 
Copper sulphate can be substituted for copper chloride. 
Place the casein and water in the bowl of the mixing machine and rotate 
the paddle slowly, stirring the mixture until all the water has been absorbed 
and all the casein moistened. If the casein is allowed to soak beforehand it is 
more readily dissolved in the mixing process. Mix the hydrated lime with water 
in a separate container. Stir this mixture vigorously at first, but just before 
it is added to the casein stir just enough with a gentle rotary motion to keep 
the lime in suspension. Pour the milk of lime quickly into the casein. 
When casein and lime are first combined they form large, slimy lumps, which 
are balls of dry casein coated with partly dissolved casein. These break up 
rapidly, becoming smaller and smaller, and finally disappear. The solution, in 
the meantime, is becoming thin and fluid. At this point stop the paddle and 
scrape the sides and bottom of the container, and then stir again. If a deposit 
of casein remains unacted on, it may cause more lumps later. 
When about two minutes have elapsed since the lime and casein were 
united, it may be noticed that the glue has begun to thicken a little. Add the 
sodium silicate now, or else the glue will become too thick. The glue will 
momentarily become even thicker, but this thickness will soon change to a 
smooth and fluid consistency. 
Continue the stirring until the glue is free from lumps. This should not take 
more than 15 or 20 minutes from the time the lime was added. If the glue 
is a little too thick, add a small amount of water. If the glue is too thin, it 
will be necessary to start over again, using a smaller proportion of water. 
The copper salt may be added at any one of several times during the mixing 
process. If added as a powder before the easein is soaked, it may have a cor- 
rosive action upon the metal container. The copper salt, if added as a powder, 
should be thoroughly mixed with the casein before the addition of the lime. 
Copper salt may be placed in solution and conveniently stirred into the mois- 
tened casein immediately before the lime is added or after all the other ingre- 
dients have been combined. If the copper solution is added at the end of the 
mixing period, pour it into the glue in a thin stream and stir the mixture vig- 
orously. Continue stirring until any lumps, which may have formed by the 
33 BUTTERMAN, S., and COOPERRIDER., C. K. Op. Cit. 
