He held his watch in his hand, so as not to make a mistake. When the fifteen minutes were over he opened the oven-door to let a current of cool air blow above the little cups. Nelly stood on a box, as she had before, and looked in through the queer board with holes in it for the eyes. The metal in the little cups was bubbling and as red as fire. Rob tried to look, but the heat hurt his eyes so he could not bear it. "Ven de cold air strike the cups," said Mr. Kleesman, "then the slag are formed." "Oh, what is slag?" cried Rob. "All that are bad go into the slag," said Mr. Kleesman. Then he put on a pair of thick gloves, and a hat on his head, and went close up to the fiery oven door, and took out the cups, and emptied them into little hollow places in a sheet of zinc. The instant the hot metal touched the cool zinc, it spread out into a fiery red rose. "Oh, how lovely!" cried Nelly. "By jingo!" said Rob. Even while they were speaking, the bright red rose turned dark,--hardened,--and there lay three shining buttons, flat and round. Their rims looked like dark glass; and in their centres was a bright, silvery spot. Mr. Kleesman took a hammer and pounded off all this dark, shining rim. Then he pounded the little silvery buttons which were left into the right shape to fit into some tiny little clay cups he had there. They were shaped like a flower-pot, but only about an inch high. "Now these must bake one-half hour again," he said; and put them into the oven. Pretty soon he opened the oven-door to let the cold air in again, as he had done before. That would make all the lead go off, he said: it would melt into the little cups, and leave nothing but the pure silver behind. "Now vatch! vatch!" he said to Nelly. "In von minute you shall see a flash in de cups, like lightning, just one second: it are de last of de lead driven avay; den all is done." Nelly watched with all her might. Sure enough, flash! flash! flash! in all three of the cups it went; the cups were fiery red; as Mr. Kleesman took them out, they turned yellow; they looked like the yolk of a hard-boiled egg hollowed out,--and there, in the bottom of each, lay a tiny, tiny silver button! Mr. Kleesman carried them into the front room and weighed them. Two of them were heavy enough to more than weigh down the little button which was always kept in the left-hand scale. That showed that the ore had silver enough in it to make it worth while to work it. The third one was so small you could hardly see it. That was the one which belonged to the old man. "You ore are not worth not'ing," said Mr. Kleesman to him. Nelly looked sorrowfully at the old man's face; but he only smiled, and said:--