44 ROYAL SOCIETY OF CANADA 
side of the constriction. Next, some finely powdered cane-sugar was 
introduced above the wool so as to form a second layer of about the 
same thickness, and then was added another layer of glass wool similar 
to the first. 
Another constriction, similar to the first, was then made 1.25 inches 
from the other end of the tube (Fig. 2, d), and a plug composed entirely 
of glass wool was placed in front. Immediately after the first con- 
striction had been made and, therefore, previously to the introduction 
of the sugar into the tube, the end of the tube f in Fig. 2, was rounded 
off in the flame and allowed to close slightly. The other end, a, was 
usually rounded off after the second constriction had been made. 

BiG. 2: 
REDUCED TO ONE HALF ORIGINAL SIZE. 
After the insertion of the plugs, two cotton wool stoppers were 
pushed into the open ends of the tube. The stopper at the end of 
the tube at which the air entered (a) was allowed to protrude somewhat, 
but that at the exit end of the tube (f) was trimmed in a flame so that 
no free hairs projected. The trimming prevented the stopper being 
pulled out during the removal of the connecting rubber tubing when 
it was necessary to take the tube back to the laboratory. The slightly 
closed condition of the exit end of the tube served to prevent the 
stopper from being sucked down the lead pipe whilst the air was being 
aspirated. 
The control tube (Fig. 2, B) was made in the same way as the ex- 
perimental except that it contained but a single plug of glass wool (e) 
and was usually one inch shorter. 
The aspirator is shown in Fig. 1. It had a capacity of twelve 
litres and was graduated in litres by means of circular markings. At 
the top and bottom of the aspirator were holes fitted with perforated 
rubber stoppers. In the perforation of the lower stopper a glass tube 
was fixed which was connected by means of a short piece of rubber 
tubing with a long glass tube which reached nearly to the ground. 
The exit of the water was controlled by means of a clamp attached 
to the rubber tubing. Through the perforation of the upper stopper 
there projected one arm of a U-shaped piece of glass tubing provided 
with two stopcocks (s and s'). 
