IOUS HAPPENINGS ON THE ISLAND

The Professor supervised every part of the operation with the utmost
care. "Before the plates are heated you must put a raised margin around
each slate square, so the molten material will not run off."

"How high shall we make the margins?"

"About a quarter inch above the surface of the slate."

"As we are now ready to heat up the crucible, how shall the materials be
mixed?"

[Illustration: _Fig. 37. Making Sheet Glass._]

"For this trial, measure out eight quarts of sand and two quarts of the
lime, and after depositing it in the crucible, we are ready for the
heat."

In a short time, with the assistance of the blower, which has already
been described, the sand began to melt. It was now stirred so that the
elements were thoroughly mingled. During the melting period the dross or
impurities which came to the top were skimmed off, and when no more of
the impurities collected the Professor stated that they might remove the
crucible and pour the melted mass into small pockets, which they had
previously formed with clay.

"Why not pour this on the slate forms we made?"

"Because we must know that we have a good sample of glass, and for the
further reason that the product we are now to make should have some
glass in it that has already been fluxed before, and we now have such a
manufactured material."

The material which had been cast in the pockets was broken up with a
hammer, as soon as it had cooled, and its appearance noted.

"I see we shall have to use less lime."

"Why?"

"You will note that it is too white or milky-like. This shows too much
lime and consequently it is very brittle."

"Suppose, on the other hand, there was too little lime, what would be
the result?"

"We should then have a glass which would not hang together at all. In
the one case, as with the present sample, with too much lime in it, we
have made a product which is closely allied to the alkaline base; and if
we had, on the other hand, too little lime, we should have something
which is nearly like quartz, hence not suitable for our purpose."

"It seems, then, we have to do in this case just as Red Angel did, make
a test sample?"

This allusion to their pet caused a smile all around.

Since the trip made by our colonists two months before they made no
effort to gain any additional knowledge of their island. What they
really knew of the country, aside from two of the trips made in the
interior, und