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drift taken a few minutes after the introduction of the expired air, assuming
in,
that an increase in drift is observed, must not be accepted at once as a positive
test for radon for it is woll known that dust particles, traces of water vapor
condensing on the insulation, or a beam of direct sunlight falling on the charged
leaf will change the natural drift. To establish positively the prosence of
radon in the expired air, readings of the drift whould be made at half hour in-
tervals over a period of two to three hours. Unless a distinct increase occurs
in the drifts corresponding to the ionization curve of radon, the test is not
positive When radon is present the drifts attain a maximum value in the course
of three hours after the introduction of the gas and the maximum for the net
drift runs about 30 per cent higher than that found initially, five to ten minutes
after the air was introdneed. To confirm further the presence of racon, the
air in the chamber should be blown out with dry, dust-free atmospheric air, and
readings taken of the drift. A distinct drop in the drift occurs when the radon
is removed from the chamber. The active deposit left on the valls and electrode
of the chamber decays rapidly and in the course of an hour or two the drift of
the instrument becomos practically normal.
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"ocrText": "-10-\ndrift taken a few minutes after the introduction of the expired air, assuming\nin,\nthat an increase in drift is observed, must not be accepted at once as a positive\ntest for radon for it is woll known that dust particles, traces of water vapor\ncondensing on the insulation, or a beam of direct sunlight falling on the charged\nleaf will change the natural drift. To establish positively the prosence of\nradon in the expired air, readings of the drift whould be made at half hour in-\ntervals over a period of two to three hours. Unless a distinct increase occurs\nin the drifts corresponding to the ionization curve of radon, the test is not\npositive When radon is present the drifts attain a maximum value in the course\nof three hours after the introduction of the gas and the maximum for the net\ndrift runs about 30 per cent higher than that found initially, five to ten minutes\nafter the air was introdneed. To confirm further the presence of racon, the\nair in the chamber should be blown out with dry, dust-free atmospheric air, and\nreadings taken of the drift. A distinct drop in the drift occurs when the radon\nis removed from the chamber. The active deposit left on the valls and electrode\nof the chamber decays rapidly and in the course of an hour or two the drift of\nthe instrument becomos practically normal."
}