i 7 o THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
vacuum was established by lowering the mercury receiver, and for a long time was a 
source of annoyance. We subsequently learned that the device had been first intro- 
duced by Lord Rayleigh. At the end of an experiment, any air which has 
collected is discharged by raising the mercury-holder, opening the screw-clip shown, 
and allowing enough mercury also to pass through to form a seal in the rubber 
tubing above the clip. 
Inflow of : 
hot water 
from bath. 
Outflow Co 
waste pipe. 
Fig. 
-Section taken through the upper portion of one tube of the Differential Densimeter and the hot- 
water jacket, showing the inflow and outflow tubes. Scale, one-third. 
The mercury-holder was suspended by means of a ring and loop of wire 
attached around the bulb from a vertical rod, swivel, and hook, possessing a slow 
screw movement in a block attached to a horizontal rod fixed in a clamp, which could 
be moved up and down on a heavy retort stand. F"or large movements, the clamp 
was slid up or down the retort standard, and for fine movements the screw was 
raised or lowered in its block. ... 
