ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
479 
86 shows the apparatus as a whole, reduced in size. Fig. 87 illustrates 
the construction of the regulator. Part A is provided with two lateral 
tubes which have an internal diameter of 6 mm., and has a ground in- 
ternal surface indicated by the stippled portion of the drawing. Part B 
is ground to fit the preceding. It is provided with an opening (1) 
through which the gas passes into the interior. The lower portion of B 
has a smaller opening (4) 1 mm. in diameter. The lower portion of 
tube B has an internal diameter of 2 mm., and when placed in position 
Fig. 86. 
Fig. 87. 
inside of A, it should come within one or two millimetres of the bottom 
of the cup. In this case, the first droplet of mercury, as it issues from 
below, shuts off the outflow of gas. The upper part of C is solid, and 
the lower part hollow. The gas enters through a large opening (2) and 
passes down to (4) the minimum outflow, and to (5) and out at (3). The 
portion marked (6) is ground to fit exactly the corresponding part in B. 
If this is not done properly, the minimum outflow of gas cannot be regu- 
lated as perfectly as it can be otherwise. The upper portion of C is a 
ground stopper fitting into B. The manipulation is simple. The gas 
