Science: Softness for Safety

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At Philadelphia's Franklin Institute last week a dummy named Oscar was catapulted headfirst against an automobile windshield. The pane cracked and some crumbs of glass fell outside the car. But when Oscar's head hit it, the pane bulged outward two or three inches. If the dummy had been a real person involved in a motor crash, this elastic yield of the glass might have saved him a skull fracture.

A nine-ounce steel ball was dropped on a pane of the same glass from a height of 28 feet. The glass bulged and cracked but did not break. A young woman stood behind another pane while Chief Bender, famed oldtime pitcher, wound up and let fly a baseball at it. The glass stopped the ball.

Thus with great fanfare was launched a new flexible safety glass, billed as the best ever. Five companies cooperated in the research which produced it—Carbide & Carbon Chemicals Corp., E. I. du Pont de Nemours & Co., Monsanto Chemical, Libbey-Owens-Ford, Pittsburgh Plate Glass. Announced cost: $6,000.000. Federal Housing Administrator Stewart McDonald, an old motormaker (Moons) but a notably inexpert motorist, made a speech. A congratulatory telegram arrived from Franklin Roosevelt.

Safety glass is a double sheet with a transparent filler or binding layer between. In the old glass the filler was cellulose acetate. In the new it is polyvinyl acetal resin, a synthetic plastic made from acetylene. In an automobile this flexible, yielding pane is something like a transparent, moistureproof, windproof curtain. It is expected to cut down the number and seriousness of highway injuries due to sudden stops.

The idea of shatterproof glass was born in 1903 when a French chemist, Edouard Benedictus, knocked a bottle containing dried collodion from a shelf. The bottle cracked but the fragments did not spatter. Benedictus concluded that they were held together by the collodion film. He got a patent in 1914 but the first shatterproof glass did not appear in automobiles until 1924.

Cellulose nitrate was the first binder used; actinic rays in sunshine turned this disagreeably brown. Cellulose acetate as a binder and actinic-filtering glass stopped the discoloration. But the glass was hard and, though it did not fly into lacerating fragments, a human head striking it fared badly. Moreover, it became brittle in cold weather. The new glass is not only soft for safety but keeps its effectiveness at temperatures around zero.