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The furnace was arched from end to end, and about the height of a tall man; the working end was like a round oven with three glowing openings; the straight part, some twenty feet long, contained the annealing oven through which the finished pieces were made to move slowly, on iron lier-pans, during many hours, till the glass had passed from extreme heat almost to the temperature of the air.
As optical glass is now made, the material is constantly stirred with an iron rod during all the time it is melting in the furnace, and after it has begun to cool, until it becomes so stiff that the stirring has to cease. It is then placed, pot and all, in the annealing furnace, where it is kept nearly at a melting heat for three weeks or more, according to the size of the pot.
The glass is then melted again, pressed into a flat disk, and once more put into the annealing oven. In fact, the operation of annealing must be repeated every time the glass is melted. When cooled, it is again examined for veins, of which great numbers are sure to be found.
=Discussion.= As in the first method, the secret of success lies in getting a square joint, and having the inner tube leave the outer one at nearly right angles. All the remarks about annealing, lumps, etc., made under the previous method apply here.
As the ends of the bars radiated into the annealing mist I saw the tentacles creep closer and ever closer to the rayless flame through which the mist flew. And at the last, as the ultimate atoms drove through, the holding tendrils were thrust almost within it; touched it, certainly. A score of times they repeated this process while we watched.
And once, the other day, as the Signor Giovanni's letter says there, he persuaded me to take his piece of gold for a beaker he saw in my hand, and I said that I would ask the master, when he came back, whether I might keep the money or not; and besides, I left the piece of money on the table in my master's laboratory, and the beaker in the annealing oven, when they came to arrest me.
But that did not matter, for the fires would now go out and the whole furnace would slowly cool, so that the annealing would be very perfect. No one but he could enter the laboratory, now that Zorzi was gone, and he could take the pieces to his own house at his leisure.
The necessity for extreme precaution in the operation of annealing will be manifest if we reflect on one of the accidents which happened. On a certain occasion, after the cooling of a great casting had been completed, it was found, on withdrawing the speculum, that it was cracked into two pieces.
In the meantime, fearing lest Giovanni might think of sending him out at any moment, he waited till Pasquale had brought him water in the morning, and then raised the stone, as he had done before, took the box out of the earth and hid it in the cool end of the annealing oven, while he replaced the slab.
Cabot and Giusippe were still discussing the Blaschka glass flowers that the Italian lad remarked: "I have wondered and wondered ever since we went out to Harvard how those fragile flower models were annealed without breaking. It must have been very difficult." "What is annealing?" inquired Jean, holding at arm's length a doll's hat and straightening a feather at one side of it. "Annealing?
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