This ones going to be short as there’s not much to add with the exception for two crucial procedures to have a valid glue.
As I’ve experimented with various number of teaspoons of canning salt and adding to the mix before cooking and after cooking I have discovered the following two.
1. Adding less than 2 teaspoons of salt will give the glue a shelf life of upto three weeks. I found this to be rather strange as one teaspoon was added and still it wasn’t enough to extend the life of the glue. I noticed two small molds appear. This is normal behaviour if it was just hot hide glue without salt or urea added to the mix.
2. Adding salt after the glue has been cooked twice gives the glue a murky appearance. Whether or not this has any adverse effect I cannot say. As I’m not sure I suggest you add the salt before it gels.