Ice for Fire

"If we could get 50 gallons of water to a forest fire immediately after we spot it from a watchtower, that would be much more effective than tons of water after the fire has had a two-or three-hour start."

This thought occurred to Acting Superintendent A. B. Everts of the Cleveland National Forest in Southern California. But 50 gallons of water weigh 416 Ib. Hauling that much weight, plus a pump and its power unit, over a mountain trail is slow work. Gasoline pumps are convenient but heavy. Forester Everts hit upon a source of power that is light and cheap as well as convenient. He tried frozen carbon dioxide, "dry ice."

Dry ice does not melt to a liquid but sublimes directly from the solid state to vapor. When this takes place under confinement, the vapor is formed at high pressure.* Everts and two associates designed a power unit consisting of two small tanks containing 25 Ib. each of dry ice. Sublimed, this delivers a pressure of 1,000 Ib. per sq. in., which is stepped down by control valves to 250 Ib. before being applied to the water hose. Last week

Forester Everts successfully tested an experimental model, returned it to the shop to iron out minor kinks. Before next summer he expects to have several full-size units on duty in the woods. Dry ice costs only 4-c- per Ib. and one filling provides enough power to empty the water tank ten times.

* One cubic inch of dry ice makes 450 cu. in. of gaseous carbon dioxide if the gas is free to expand at atmospheric pressure.

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