Mark Kinsler wrote, "I wonder if anyone has ever tried to adapt
a hot-melt glue gun for hot hide glue. Might work if the temperature
was controlled well enough."

No need to bother.  I just use my specially made glue bottles.  I never
have to adjust the thickness of the glue if it was made up correctly in
the first place.  I use one bottle for 10-15 minutes, put it back, and
use the next one.  No more open pot glue.  I kept the liner just in
case I ever want to make an actual pot of glue but in the last 6 years
it has not happened.  I keep a dozen bottles of glue made up in the
fridge and ready to heat and use.  They are available at my web site
below under supplies.

D.L. Bullock    St. Louis
Piano World
http://www.thepianoworld.com/