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The Vast Abyss, a fiction by George Manville Fenn |
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Chapter 13 |
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_ CHAPTER THIRTEEN. "I haven't got a dictionary here, uncle," said Tom, with a smile, as they stood at the massive table under the window in the laboratory. "I don't know what elutriation means." "I dare say not. I didn't till I was nearly fifty, Tom, but you soon shall know. Fetch that tin off the shelf." Tom obeyed, and found a label on the top, on which was printed "Best Ground Emery." "Well, you know what that is?" "Emery? Powdered glass," said Tom promptly. "Wrong. Diamond cuts diamond, Tom, but we want something stronger than powdered glass to polish itself. Emery is a mineral similar in nature to sapphire and ruby, but they are bright crystals, and emery is found in dull blocks." "Then it's very valuable?" said Tom. "Oh, no. It is fairly plentiful in Nature, and much used. Now then, we want coarse emery to grind our speculum after we have done with the sand, and then different degrees to follow, till we get some exquisitely fine for polishing. How are we to divide the contents of that tin so as to graduate our grinding and polishing powder?" "Sift it, of course, uncle." "And where would you get sieves sufficiently fine at last?" "Muslin?" "Oh, no. Here is where elutriation comes in, Tom; and here you see the use of some of the things I brought back from London the other day. To work. Bring forward that great pan." This was done. "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." They descended, leaving the pan standing on the heavy table, and after spreading wet sand upon the lower disc of glass, the loose one was once more set in motion, and uncle and nephew, with quarter-hour rests for examination and wetting the surfaces, patiently ground away for an hour, by which time, upon the speculum being sponged, it was found that the greater part of the upper glass was deeply scratched. "This is going to be an awfully long job," thought Tom. "Yes, it is," said his uncle, who aptly read his thoughts, "a very long job, Tom; but good things have to be worked for, boy." "Oh, I'm not going to be tired, uncle. It's like working for a grand prize." "It is. Now then, let's see to the emery. Our finest must be ready by now. Now I want all the water, from which the emery has settled down to the bottom, drawn off into that great white basin. How is it to be done?" "Pour it off," said Tom. "No; couldn't be done without disturbing the bottom. Let's try syphoning." Uncle Richard placed the basin upon a stool below the level of the table, took up a glass tube bent somewhat in the shape of a long-shanked hook, placed the short end gently beneath the surface of the nearly clear water, his lips to the long end, drew out the air, and the water followed directly from the atmospheric pressure, and ran swiftly into the basin. As it ran, and Tom watched, Uncle Richard carefully held the short arm of the syphon, guiding it till the sediment at the bottom of the pan was nearly reached, when he quickly withdrew it, and the basin was then placed beside the pan. "There, Tom," said Uncle Richard, "that's our sixty-minute emery." "But I thought you said you wanted it very fine. You've only washed it." "We're playing at cross purposes, Tom," said Uncle Richard. "You are talking about the contents of the pan, I about those of the basin." "What! the clear water--at least nearly clear?" "Ah, there you have hit it, boy--nearly clear. That water contains our finest polishing powder, and it will have to stand till to-morrow to settle." "Oh!" said Tom, who felt very much in the dark, and he followed his uncle to the neat sink that had been fitted in the laboratory, and helped him wash a series of wide-mouthed stoppered bottles, which were afterwards carefully dried and labelled in a most methodical way. "Saves time, Tom, to be careful," said Uncle Richard, who now took up a pen and wrote upon the label of the smallest bottle "Emery, 60 min." "There, that's for the contents of the big basin." "Want a genii to get a pailful into that little bottle, uncle," said Tom, laughing. "We'll get all we want into it to-morrow, Tom," was the reply. "Now then, how do you feel--ready for one hour's more grinding at the speculum, or shall we leave it till to-morrow?" "I want to finish it, and see the moon," said Tom sturdily, as he rolled up his sleeves a little more tightly. "Let's get on, uncle, and finish it." "Or get an hour nearer," said Uncle Richard; and they went down and ground till Mrs Fidler summoned them to their meal. _ |
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