Dr. Dupré asked Dr. Debus how it was that a molecule of pentathionate could be re-crystallized, whereas two molecules of pentathionate, which should, when half decomposed, furnish a molecule of tetra and a molecule of pentathionate, could not. Dr. Armstrong then read a _"Preliminary Note on some Hydrocarbons from Rosin Spirit."_ After giving an account of our knowledge of rosin spirit, the author described the result of the examination of the mixture of hydrocarbons remaining after heating it with sulphuric acid and diluting with half its volume of water and steam distilling. Thus treated rosin spirit furnishes about one-fourth of its volume of a colorless mobile liquid, which after long-continued fractional distillation is resolved into a variety of fractions boiling at temperatures from 95° to over 180°. Each of the fractions was treated with concentrated sulphuric acid, and the undissolved portions were then re-fractionated. The hydrocarbons dissolved by the acid were recovered by heating under pressure with hydrochloric acid. Besides a cymene and a toluene, which have already been shown to exist in rosin spirit, metaxylene was found to be present. The hydrocarbons insoluble in sulphuric acid are, apparently, all members of the C_nH_{2n} series; they are not, however, true homologues of ethylene, but hexhydrides of hydrocarbons of the benzene series. Hexhydro-toluene and probably hex-hydrometaxylene are present besides the hydrocarbon, C_10H_20, but it is doubtful if an intermediate term is also present. It is by no means improbable, however, that these hydrocarbons are, at least in part, products of the action of the sulphuric acid. Cahours and Kraemer's and Godzki's observations on the higher fractions of crude wood spirit, in fact, furnish a precedent for this view. Referring to the results obtained by Anderson, Tilden, and Renard, the author suggests that rosin spirit perhaps contains hydrides intermediate in composition between those of the C_nH_{2n-6} and C_nH_{2n} series, also derived like the latter from hydrocarbons of the benzene series. Finally, Dr Armstrong mentioned that the volatile portion of the distillate from the non-volatile product of the oxidation of oil of turpentine in moist air furnishes ordinary cymene when treated in the manner above described. The fact that rosin spirit yields a different cymene is, he considers, an argument against the view which has more than once been put forward, that rosin is directly derived from terpene. Probably resin and turpentine, though genetically related, are products of distinct processes.