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DUST AND DISEASE. 283

charged with floating matter ; at the end of half an hour it
was optically empty.

A second experiment was thus arranged: on the wooden
'base of a cubical glass shade, measuring 11%— inches a side,
upright supports were fixed, and from one support to the
other 38 inches of platinum wire were stretched in four
parallel lines. The ends of the platinum wire were soldered
to two stout copper wires, which passed through the base
of the shade and could be connected with a battery. As
in the last experiment, the shade rested upon cotton-wool.
A beam sent through the shade revealed the suspended
matter. The platinum wire was then raised to whiteness.
In five minutes there was a sensible diminution of the mat-
ter, and in ten minutes it was totally consumed. This
proves that when the platinum wire is sufficiently heated,
the floating matter, instead of being distributed, is destroyed.

But is not the matter really of a character which permits
of its destruction by the moderately-heated platinum wire ?
Here is the reply:

1.6 A platinum tube, with its plug of platinum gauze,
was connected with an experimental tube, through which a
powerful beam could be sent from an electric lamp placed
at its end. The platinum tube was heated till it glowed
feebly but distinctly in the dark. The experimental tube
was exhausted, and then filled with air which had passed
through the red-hot tube. A considerable amount of float-
ing matter which had escaped combustion was revealed by
the electric beam.

2. The tube was raised to brighter redness and the air
permitted to pass slowly through it. Thoughdiminished
in quantity, a certain amount of floating matter passed into
the exhausted experimental tube.

3. The platinum tube was rendered still hotter; a
barely perceptible trace of the floating matter now passed
through it.

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