“Now empty in the contents of this packet.”
Tom took up a little white paper of something soft, opened it, and poured the contents into the pan.
“Powdered gum arabic?” he said.
“Yes. Now empty the tin of emery upon it.”
Tom opened the tin, and found within a dark chocolate-looking powder, which felt very gritty between his finger and thumb. This he emptied upon the gum arabic, and, in obedience to instructions, thoroughly mixed both together.
“To make the fine emery remain longer in suspension,” said his uncle, “keep on stirring, Tom.”
“All right, uncle. What, are you going to pour water in? It’s like making a Christmas pudding.”
For Uncle Richard took up a can of water, and began to pour a little in as Tom stirred, changing the powder first into a paste, then into a thick mud, then into a thin brown batter, and at last, when a couple of gallons or so had been poured in and the whole well mixed, the great pan was full of a dirty liquid, upon the top of which a scum gathered as the movement ceased. This scum Uncle Richard proceeded to skim off till the surface was quite clear, and then he glanced at his watch.
“Is that scum the elutriation?” said Tom, with a faint grin.
“No, boy, the impurity; throw it down the sink. Now, Tom, we want to get our finest polishing emery out of that mixture, and it will take an hour to form—sixty-minute emery, the opticians call it; so while it is preparing, we’ll go and have another turn at the speculum.”