428 WALLACE LARKIN CHANDLER 
paraffin is used for effecting an air-tight seal. It was thru this opening 
that animals were introduced into the tank, thus obviating the necessity 
of removing the entire cover each time. A small glass window was also 
built into one side of the tank, thru which observations of the temperature 
inside could be made. The tank rests on two runners, one of which is 
lower than the other in order to provide a slant to facilitate drainage of 
urine thru a smali hole in one corner of the bottom of the tank. A false 
removable bottom 1 inch in height, made of strong wire of No. 2 mesh 
and well supported, was constructed in three pieces, for ease in handling. 
This false bottom serves to keep the animal from contact with its exeretions. 
Two parallel steel supports are placed across the width of the tank 14 
feet above the bottom, and on the middle of these supports rests a wire 
cage 8x 8x 10 inches. This cage serves to protect a small fan, which is 
connected to a motor on the outside by a shaft passing thru a tightly 
fitting collar in one side of the tank. This cage also protected a triangular 
strip of cheesecloth from which the nitrobenzene was evaporated. The 
container into which the cheesecloth dipped rested on an aluminum 
tray in the bottom of the cage. The inside of the tank and all its internal 
accessories were coated with paraffin in order to prevent rusting. 
TECHNIQUE 
Obtaining pure nitrobenzene 
Practically pure nitrobenzene was obtained by redistilling the commercial 
liquid, at the temperature of the boiling point of nitrobenzene, until 
a product was obtained which proved experimentally to have a boiling 
point and a freezing point corresponding to pure nitrobenzene (page 412). 
Aeration of the fumigation chamber 
The tank was aerated by passing air saturated with nitrobenzene into 
it at a rate determined by the weight of the animal being fumigated. 
The air was saturated by passing it, after dehydration, thru a flask con- 
taining nitrobenzene and kept at a temperature of 50° C., and condensing 
it by passing it thru a series of U-tubes containing nitrobenzene. The 
final condensing tubes were placed inside the tank, so that the final con- 
densing temperature equaled the temperature of the tank. 
