BUBBLES
If you should notice white bubbles, in the shape of round blots, on the surface of the glue, you have found evidence of decay. If there is any doubt in your mind you can complete the evidence by moistening the glue. If it gives off a sour odor you have an additional indication of putrefaction. Such glue should be avoided.
Bubbles may appear within the glue—not on the surface—without being an indication of putrefaction. As a matter of fact, bubbles are practically always found in certain high-grade glues, though practically never in low-grade bone or hide glues. They are supposed to be due to the air which gets in when the glue is poured into the moulds. When glue is originally dried on nets in very cool and dry weather, such bubbles are frequently found. Always beware of glue showing surface bubbles.