and affords a "breeding place for the "bacteria of decomposition, exposing 
the fresh "batches to the constant danger of "becoming contaminated. Glue 
pots should "be washed every day and cnly enough glue for a day's run should 
be mixed at a time. If these simple, sanitary precautions are not observed, 
poor joints are more than likely to result. 
In a brief review, it is not possible to cover thoroughly all the 
points touched upon, or even to mention many facts which the glue user should 
know. For more detailed treatment of the subject, with information on animal 
glues and other types as well, the reader is referred to the publications 
listed on page 9» 
Liquid Glues 
Most of the commercial liquid glues are made from fish stock — 
heads, bones, skins, and swimming bladders — although several brands of 
animal glue in liquid form are on the market. Liquid glue can be used cold 
and spread without any preparation whatsoever. Commercial liquid glues vary 
widely in strength; some are so weak as to be suitable only for use on paper 
jT cardboard, while others are almost as strong as high-grade dry animal 
glue. 
Liquid glues are used to a certain extent in joint work, but not 
of the highest class. They are used also for repair work and miscellaneous 
purposes « Liquid glues would be used more extensively if they were less 
expensive and if the better grades could be readily and accurately distin- 
guished by the user. 
Testing Liquid Glues 
Methods of testing liquid glues have not been standardized. 
Tests of joint strength on liquid glues have indicated that the very thin, 
watery liquid glues tend to produce weak joints, but no definitely con- 
clusive relation appears to exist between viscosity and joint strength. 
Tressler (10) has suggested the following tests for liquid glues from fish 
stock: Viscosity, ash content, drying properties, hygroscopicity, joint 
strength, color, permanence, and pH value. Jennings (6) holds that liquid 
fish glues should have the following properties: Be neutral to litmus, 
slightly acid to phenolphthalein, remain unaltered after one month's storage 
at 37°-3 8 ° C., set to a jelly between 7. 5° and 10° C, be free from tackiness 
when exposed in film form at 25° C. to 80 percent relative humidity, and 
contain not more than 0.2 percent chlorides. 
Since the importance or value of the various chemical and physical 
properties of liquid glues are not well established and since standardized 
test procedure for their determination is not available it is necessary to 
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