As is well known, the molecular depression of the freezing-point of aqueous solutions of electrolytes is greater than 1·87, van't Hoff's constant, with which the molecular depressions of nonelectrolytes have been found to agree extremely well. This is in accordance with the dissociation theory; and for binary electrolytes the molecular depression may approximate to 1·87 × 2, for ternary electrolytes to 1·87 × 3, etc., but cannot exceed these values.

Substances such, as potassium ferrocyanide, which, according to the dissociation theory, might be expected to give values approximating to 1·87 × 4 or 1·87 × 5, have not been found to give molecular depressions greater than 1·87 × 3. This has been held to be an objection to the dissociation theory.