Place in the can a mixture of 2 oz.
black oxide of copper, 1 oz. black oxide of manganese and some
iron filings.
Purchase a small crowfoot zinc and hang it about 1 in. above the
half can. Prepare a 10 per cent solution of caustic soda and fill
the jar within 1 in. of the top. Place on top the solution a thin
layer of kerosene or paraffin. The cell will only cost about 50
cents to make and 25 cents for each renewal. When renewing, always
remove the oil with a siphon.
--Contributed by Robert Canfield, University Park, Colo.
** A Home-Made Barometer [151]
Take 1/4 oz. of pulverized campor, 62 gr. of pulverized nitrate of
potassium, 31 gr. nitrate of ammonia and dissolve in 2 oz.
alcohol. Put the solution in a long, slender bottle, closed at the
top with a piece of bladder' containing a pinhole to admit air,
says Metal Worker. When rain is coming the solid particles will
tend gradually to mount, little crystals forming in the liquid,
which otherwise remains clear; if high winds are approaching the
liquid will become as if fermenting, while a film of solid
particles forms on the surface; during fair weather the liquid
will remain clear and the solid particles will rest at the bottom.
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