More than a half-century ago, Wheatstone, in experimenting with the electro-chemical behavior of certain elements, laid the foundation for the modern chemical rectifier. In the year 1855, he found that aluminum as anode in certain electrolytes, offered great resistance to the passage of the electric current, while as kathode, offered very little. This experiment was repeated two years later by Buff. He thought he observed that when the aluminum was used as the anode, that a dark skin formed upon its surface. This was verified by Beetz in 1877. Talt, in 1869, observed a high counter E.M.F. Overbeck and Streintz considering the film as a non-conductor, separating two conductors, the electrolyte and plates, saw in the arrangement a typical condenser. This application was studied and developed until within the last few years, but has not yet been brought to the point of utility.