The author describes various experiments made with a view to determine the electro-chemical equivalents of sodium and potassium. Three experiments gave, respectively, 22.3, 22.9, and 25, as the equivalent of the former; and two other experiments gave, respectively, 45 and 41.7, as the equivalent of the latter of these substances. He then inquires what would be the result of the electro-lyzation of the aqueous solutions of soda and potash, on the hypothesis of these bodies being composed of two equivalents, or atoms, of metal, and one of oxygen. To determine this question he employs a solution of dichloride of copper in muriatic acid, as being a substance composed of two atoms of metal and one of an electro-negative element. Its electrolysis gave as the equivalent of copper, 52.8, 59.4, and 61.6, numbers approximating closely to 63.2, or double the atomic weight of copper. After a long train of investigation, he concludes that there is no reason deducible from the theory of isomorphism for doubting the correctness of the received atomic weights of silver, sodium, &c., but that the difficulty, or anomaly, if it may be so called, should be considered as attaching itself to the di-compounds of copper; and that Faraday’s propositions on this subject remain unimpeached.