This is my 1st hatch and feel more anxious than when I was pregnant with my own kids. Yesterday, we had 2 chicks hatch (day 21) but noticed our 3rd had started to zip but stopped progress and the membrane was bone dry.  Even The sponges I had put in to help keep humidity were curled dry!  A few weary hours of trying to keep her hydrated to hatch, she passed. I found this thread, and gained some hope. 
Early this morning, we did the float test on our remaining eggs. 3 sunk  to the bottom right away, but we had 11 eggs wiggle.  Maybe it wasn't too late. I refilled the channels with water and added a sponge also and put the wiggles back in. I am now hearing faint peeps in the bator.   Feeling hopeful...