Marine Ecology Laboratory Fisheries Research Board of Canada Bedford Institute Dartmouth, Nova Scotia
I
A Mercury Dispenser
I
Mercury is often used to calibrate volumetric apparatus, such as the capillary volume of dilatometers. The problem is to devise a dispenser that allows one not only to weigh Hg but also to dispense it from the same container. Figure 1 is a diagram of a simple and inexpensive Hg dispenser which I use. It is constructed from a piece of 7-mm od Pyrex glass tubing. The od is slightly enlarged near the top half of the dispenser. The dispenser is about 20 cm long and it has a capacity of about 15 g of Hg. The basic design can be modified easily if the need arises. Hg is introduced through a small opening which is located at the enlarged part of the dispenser. A small glass bead, located a t the bottom, acts as a stopper; it is fused on platinum wire (0.30 in.) which extends through the other end. The bead is under tension from a small stainless steel compression spring which is slightly compressed and held in place by a small locking-collar. The end of the wire is hooked so that the dispenser can be hung from the top of 'DUEDALL, I. W., 528-531 (1965).
AND
WEYL, P. K., Rev. Sci. Instrum.,
P Locking-collar and C a p Compression Spring
.
Opening ( f i l l herel
Platinum
Wire
Pyrex Glass Tubing
Gloss
Bead
Iho mercury dirpansar.
the Dan of an analvtical balance. The steps in using the dispenser are: (a) the dispenser, containing some Hg, is weighed; (b) the Hg is dispensed into the aDparatus by depressing the spring; and (c) the dispenser is reweighed. Sometimes a tiny droplet of Hg will stick to the outside edge of the dispenser after Hg is dispensed. This difficulty is overcome by beveling the end of the tubing (see figure) with a fine carborundum sharpening stone. The dispenser can also he used for dispensing nonhygroscopic salts.'
Volume 45, Number 6, June 1968
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393
