A study has been made in this laboratory of the solubility in water of several series of slightly soluble organic compounds. Such systems are sufficiently dilute so that but little interaction is to be anticipated between the solute molecules themselves. They thus afford an opportunity to study the interactions between the solvent water molecules and the organic molecules as reflected in the solubility values and their change with temperature, and in the energy values associated with the solution process.The solubilities of several simple series of compounds, including aromatic hydrocarbons and halogenated aliphatic and aromatic hydrocarbons, have been measured, as well as of the series of aliphatic ketones for which data are given here. The ketones, while showing more complicated relationships, are presented here, since in the results for them certain interesting features are evident that are present in only a limited degree in the other cases.The experimentally determined solubility values are the concentrations in the water phase in equilibrium with the liquid solute phase, saturated with water. Inspection of these values shows but little correlation to exist among them in any of the series of compounds. However, when those energy terms involved in separating the solute molecules from their liquid phase are eliminated, regularities become evident at once. This may be done by recomputing the observed solubilities to vapor solubilities corresponding to a constant standard state of 100 mm. in the vapor. To compute these standard vapor solubilities from the observed solubility values and the vapor pressures of the organic liquids, Henry's law is employed. Except in a few cases (3) this law has not been commonly applied to such systems. While there seems little reason to doubt its validity in the case of dilute solutions, it was deemed better to determine