1896] LABORATORY APPARATUS IN VEGETABLE PHYSIOLOGY 471 
The apparatus is not accurate, but makes an interesting 
demonstration of the general difference in transpiration between 
the two sides of different kind of leaves. 
Slide with binding posts.— 
The difficulty in attaching wires 
to tin foil, when wishing to use 
an electric current under the 
microscope, has led to the device Fic. 5. Slide with binding posts. 
shown in fig. 5. An ordinary. 
microscope slide is provided with a pair of small brass binding 
posts, each bearing a clip. When in use two wedge shaped 
pieces of tin foil are placed under the clips with their points 
near together. The object to be examined is mounted ina drop 
of water between the points, and covered with a cover slip in the 
usual manner. It is then placed on the stage of the microcope 
and the wires from the battery passed into the binding posts. 
Mercury reservoir.— Mercury is often serviceable and occasion- 
ally indispensable in physiological work. Sometimes, as in eudio- 
metric experiments, it must be dry and 
perfectly clean. The several ways of 
cleaning mercury are mostly tedious and 
unsatisfactory, and repeated trials led 
finally to the adoption of a reservoir that 
keeps the mercury always dry, clean, and 
ready for use. 
The reservoir consists of a thick walled 
glass separatory funnel, about 15™ in 
diameter (fig. 6). In this the mercury 
with some mercurous sulfate is placed, 
together with enough concentrated sul- 
furic acid to make a quarter-inch layer 
over the surface. To begin with it is 
Me. 6, Mercury reservoir. shaken up several times, and in twenty- 
four hours is ready for use. Mercury drawn 
from the bottom is pure and dry. After use it is returned to ass 
voir where it again becomes usable, without further attention. 
