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Answers to Correspondents.
_Correspondents who expect to receive answers to their letters must,
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head of "Business and Personal"
All reference to back numbers should be by volume and page._
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J. F. McK., of Md.--"What kind of silk is used for balloons, what is the
varnish which covers them, and what amount of common illuminating gas
will support one pound weight?" Silk for large balloons is now rarely
used, stout cotton cloth being substituted. Ordinary boiled linseed oil
makes a good varnish. Any elastic varnish will do, however. The specific
gravity of ordinary illuminating gas ranges from 0.
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