The total cost of materials for constructing the apparatus complete will not amount to more than one dollar.
Contributed by M. G. Kopf, Lewis Institute, Chicago.
Weatherproofing for Tents
Dissolve 4 oz. sulphate of zinc in 10 gal. water; add 1/2 lb. sal-soda; stir well until dissolved, and add 1/2 oz. tartaric acid. Put the tent cover in this solution and let lie 24 hrs. Take out (do not wring it) and hang up to dry.
Grinnell's Hand Book on Painting.
Sawing Sheet Metal
Sheet metal placed between two boards in the jaws of a vise and clamped tightly, can be sawed easily with a hacksaw.