An Antifoam for Polarographic Maximum Suppressors The most widely recommended polarographic maximum suppressor, Triton X-100 (manufactured by Rohm and Haas Co., Philadelphia, Pa.), is a n efficient foaming agent. When a solution containing this surfactant is purged with inert gas, a penistent foam forms on the surface of the solution. De-aeration then must be quite slaw, so as to form the foam no faster than it breaks; otherwise some of the faam and solution will he pushed out of the palarographic cell. Often the time required for deaeration is extended from2 min to 10 mi". We have discovered that a trace of silicone grease will rapidly break this foam, no doubt because silicone oil, a well-known antifoam, spreads over the foam. It is sufficient t o put the least amount af silicone stopcock grease that can be felt on one's index finger, and to wipe the finger over the inner surface of the polarographic cell above the level of the solution. De-aeration can then proceed a t the same rate as in the absence of maximum suppressor, while the height of the foam never exceeds a quarter of an inch. The cell can he emptied and refilled many times before the film of grease is depleted. We naturally feared that the silicone oil might reach the surface of the dropping mercury electrode and interfere with the faradaie process there, hut we have run several dozen polamgrams in aqueous solutions without noticing any distortions of the waves. Apparently the solubility of silicone oil in water is so law that no detectable amount can reach the surface of a d.m.e. during the life of a drop. However, if a nonaqueous solvent or a fixed electrode such as a hanging mercury drop were used, contamination of the surface of the electrode would be mare likely. Grand Valley State Colleges Allendale, Michigan 49401
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Journal of Chemical Edocafion
Wolfgang U.Spendel Victoria A. Spendel J o h n G. MeCullough
