2Q Messrs. Wright and Thompson on the Determination of 
rpipe into the U-shape re})resented 
drawn out before the bl( 
The glass being 
Fier. 1. 
on about two thirds scale in the cut (fig. 1) 
perfectly dry and hot, pure recently-boiled 
still hot mercury was poured into them so 
as to form a layer about half an inch (10 
to 15 millimetres) deep, a; on the top of 
this was then poured a boiling paste of 
thoroughly well- washed mercurous-sulphate 
and zinc-sulphate solution, containing so 
much of the latter salt as to be slightly su- 
persaturated when cold, so as to crystallize 
on standing. It was found convenient to 
make the paste not too thick, and to let the 
solid matter subside in the cell, the su- 
pernatant comparatively clear fluid being 
sucked out by a clean pipette, so as 
finally to leave on the top of the mercury 
a layer of particles of mercurous sulphate wetted with zinc- 
sulphate solution some 15 to 20 millimetres deep, b. Pieces 
of zinc rod (cast in glass tubes from pure metal fused in a 
porcelain crucible), well brightened by a file that had never 
touched any other metal, were then placed in the cells so as 
to dip into the paste some 4 or 5 millimetres, and project out 
of it about twice as much, c. The zincs were kept from falling 
by pieces of cork, d, cut as represented in fig. 2, and pre- 
viously immersed in hot paraffin-wax so as to expel 
air and moisture ; to the ends projecting from the 
paste were previously soldered copper wires, e. 
Melted paraffin-wax was then poured into the cell 
so that all air was expelled, rising through the 
perforations in the edges of the cork disks, and so that 
the upper two thirds of the zinc and the soldering were 
completely covered,/. Finally, a piece of platinum wire, <?, or 
a strip of foil was passed down the narrow limb of the cell so as 
to make contact with the mercury : it was found convenient 
to amalgamate the tip of the platinum by moistening it and 
immersing it in freshly made sodium amalgam, all sodium 
being removed from the adherent film of mercury by subse- 
quent immersion in water for some hours. The cells thus 
prepared, being wanted for use only and not being required 
to be externally well finished, were not mounted in the neat 
brass cases with ebonite tops and binding-screws usually em- 
ployed, but were simply fixed in a beaker, or any other 
convenient holder, by pouring in melted paraffin-wax around 
them. When used in connexion with the electrometer, the 
copper wire soldered to the zinc and a similar wire soldered 
