1913] KNIGHT & CROCKER—TOXICITY OF SMOKE 3390 
METHOD OF EXPOSING TO GASES AND VAPORS‘ 
The exposure to gas or vapor was made in galvanized iron cans 
of the type shown in fig. 1, and of three capacities, 10, 50, and 100 
liters. Each can consists of two pieces, the can proper and the 
bottom. The can proper has at a a side tube bearing a no. 
two-holed rubber stopper. The stopper is equipped with glass 
tubes, rubber tubes, and screw clamps. The lower edge of the 
can has an out-turned brim, 1 cm. wide, at right angles to the 
sides of the can; this gives the can close continuous contact with 
the bottom. The bottom is a 
galvanized iron disk with 3 mm. 
of the edge turned up at right 
angles to the plane of the disk. 
The brim of the can fits closely 
inside the upturned margin of 
the bottom. To seal a culture 
in the can, it is placed on the 
bottom piece, the can set in 
position, and the gutter above 
the brim of the can carefully 
sealed with molding clay mixed 
with vaseline in such propor- 
tions as to give the desirable 
consistency. The seal will hold 
against a very considerable un- 
equal pressure of gas. Vaseline was chosen as the mixing medium 
because it does not give off any fumes injurious to the seedlings 
and makes a material that maintains the same consistency after 
years of use. If the gas studied required the use of only a few cc., 
it was forced in through one of the tubes at a under a small head 
of mercury or water. Mercury was used in case the gas was very 
soluble in water, otherwise water was used. If a larger volume of 
the gas was required, suction was applied to one of the tubes at a, 
Fic. 1.—Apparatus for exposure to 
gases and vapors: explained in text. 
* The description of methods here will cover the whole field of work, thereby 
avoiding redescription in later papers. For that reason many matters mentioned 
here do not apply to the work on smoke. 
