EVOLUTION OF T H EQUILIBRIUM ~ SYMBOL AS USED IN CHEMISTRY JOHN P. HEWLETT, JR.' and C. VERNE BOWEN
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Bureau of Entomology a n d Plant Quamntine, Beltsville Research Center, M a y l a n d
THE conventional equation sign (=) in chemical. equations has within the last thirty years been replaced to a large extent by two arrows (*) showing revmibility of a reaction. Both t h e l e n g t h ( z ) a n d the thickthe shafts of the have been used to ness (*) designate the direction in which the reaction tends to go to completion. The top arrow signifies the original direction of the reaction. usageof the two arrows, modified so that they may lie closer together, has resulted in the removal of the lower barb of the upper arrow and the upper barb of
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Present address: National Bureau of Standards. Washingtan, D. C.
the lower arrow. This symbol (=)has found wide usage in modern chemical literature. In line with this development, we offer the suggestion that only one double-barbed horizontal line or shaft be used to denote a reversible reaction. This is accomplished by superimposing the shafts of the arrows" (4). The upper barb would indicate the original direction of the reaction and the length of the barb j - l j or its thickness (would l ) show the dominant tendency. It appears that the use of this simplified symbol should facilitate the writing of chemical equations.
