How does Gandalf use the beater to escape from the goblins? Need text evidence

Gandalf and Thorin used Biter and Beater to frighten the goblins chasing them through the tunnel. 

At this point Gandalf fell behind, and Thorin with him. They turned a sharp corner. "About turn!" he shouted. "Draw your sword, Thorin!"

"There was nothing else to be done; and the goblins did not like it. They came scurrying round the corner in full cry, and found Goblin-cleaver and Foehammer shining cold and bright right in their astonished eyes. The ones in front dropped their torches and gave one yell before they were killed. The ones behind yelled still more, and leaped back knocking over those that were running after them. "Biter and Beater!" they shrieked; and soon they were all in confusion, and most of them were hustling back the way they had come."

Gandalf used Beater's bright blue light to help them escape.

"Then Gandalf lit up his wand. Of course it was Gandalf; but just then they were too busy to ask how he got there. He took out his sword again, and again it flashed in the dark by itself. It burned with a rage that made it gleam if goblins were about; now it was bright as blue flame for delight in the killing of the great lord of the cave. It made no trouble whatever of cutting through the goblin-chains and setting all the prisoners free as quickly as possible. This sword's name was Glamdring the Foe-hammer, if you remember. The goblins just called it Beater, and hated it worse than Biter if possible. Orcrist, too, had been saved; for Gandalf had brought it along as well, snatching it from one of the terrified guards. Gandalf thought of most things; and though he could not do everything, he could do a great deal for friends in a tight comer."