A recent trial of a smoke rocket for testing drains, described by Mr.
Cosmo Jones in the _Journal of the Society of Arts_, is deserving of
interest. The one fixed upon is 10 in. long, 2½ in. in diameter, and with
the composition "charged rather hard," so as to burn for ten minutes. This
gives the engineer time to light the fuse, insert the rocket in the drain,
insert a plug behind it, and walk through the house to see if the smoke
escapes into it at any point, finishing on the roof, where he finds the
smoke issuing in volumes from the ventilating pipes. The house
experimented upon had three ventilating pipes, and the smoke issued in
dense masses from each of them, but did not escape anywhere into the
house, showing that the pipes were sound. If the engineer wishes to
increase the severity of the test, he throws a wet cloth over the top of
the ventilating pipe, and so gets a slight pressure of smoke inside it.
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