,646 



THE POPULAR SCIENCE MONTHLY. 



have to be introduced, then instantly opened for the introduction, and 

 as instantly closed after the introduction. It was equally requisite to 

 guard the entrance into the chamber, so that the men employed in 

 pushing in the cage should be protected from the vapor. A method 

 had also to be adopted by which it could be known when all the ani- 

 mals had ceased to breathe. 



To meet the first of the above-named conditions, I constructed the 

 lethal chamber (the outline of which is shown in Fig. 1) of well-sea- 



FiG. 1.— TuK Lethal Chamber. 



soned timber, making every part of it a double wall, and filling the 

 interspace closely with sawdust. 



In order to obtain the slight excess of space which was wanted to 

 insure diffusion, I formed on each side of the chamber an extra space, 

 which I call a pocket. They are in the center on each side, and stand 

 out as aisles from a central nave. 



In order to secure quick and equal distribution of the vapors 

 through the chamber from the stove, I let the gases in at first from 

 the top, under the impression that the gases, being heavier than the 

 atmosphere, would be made to pass with greater rapidity into all parts. 

 Theoretically, this view is correct ; but, as it became necessary to 

 have two floors or tiers to the cage, I was obliged, in the end, to let 

 in the gas half-way down the sides of the chamber. By using two 

 stoves, one on each side, this method of introduction was both con- 

 venient and effective. To remove the common air, an opening, with 

 a shaft of ten feet, was made in the roof. The shaft has a bore of 

 three inches, and has a cap at the top, in order to prevent down-cur- 

 rents of air. At the foot of the shaft is a damper, which can be 

 opened and closed at pleasure. 



