23

Experiment VIII.

        Another experiment was tried with the following alterations: (1) the fan was
worked; (2) the tubes leading off from the main tube were larger in calibre and
their total surface area equal to the surface area of the large tube leading from
the generator, so that the full amount of gas was delivered into the room. There
were nine pipes altogether: five delivered into the room at different heights and
four were inserted into the four burrows, and the mouths of the burrows where
the pipes were inserted were choked up.

        Three hundred and forty grammes of 98 per cent. potassium cyanide was
decomposed. The resultant hydrocyanic acid gas calculated to be about 4.38
cubic feet at 26° Centigrade was delivered into the room of about 1,640 cubic feet
capacity. The amount of potassium cyanide used would be equivalent to about
¾ oz. to 100 cubic feet air space. There was 35 minutes' exposure to the gas.
By means of the observation rods the room was seen to be sufficiently free
from the gas five minutes later. Forty minutes, therefore, were taken for the
whole experiment. After the fumigation the fleas were examined at once and also
three hours later to see whether they had revived.