OK guys, you wanted answears. I made glue from hoof, but it was not just the shell. It will make glue, and it does work. I decided to do a little experementing to see what works and what don't, to answer all the controversy. I also did a lot of reading.
Hoof shell, will not make glue adequate to build anything except postage stamps, and that is questionable.
Entire hoof, including toe bones and all the other material in the hoof (digital cussion, pieces of the flexor and extensor tendons) will make glue adequate to build bows.
Sinew makes good glue. The older the animal the better the glue. It will gel faster and hold better.
Bone will make glue.
Hide glue is stronger than bone glue.
Fish glue is the strongest and most flexable, but is most susceptible to humidity.
Blood glue is fairly strong, and makes the most water resistant glue.
You can also make glue from vegetable starch, milk and numerous other things.
I suspect that hoof glue was actually everything glue. The inner hoof was good, but hard to get out, so throw the whole leg in. It is primarily a wood glue.
Fish glue is used to glue flexable joints, it is used to glue leather seams.
Blood glue is the best high pressure glue. It was used for plywood construction.
Vegetable glues are used for envelopes and such.
Animal glue from hide or sinew is stronger than Knox. I don't know if it is because Knox has been treated to be clear and odorless with chemicals, but that is my suspicion.
Animal glue is considered instant glue, because it holds as soon as it cools. Long before it is dry.
Animal glue is stronger than TB.
Because it gels first, then dries, it does not honey comb like the synthetic water based glues.
Justin