It is the same with gaseous hydrofluoric acid. Finally we may add that the hydrofluoric acid employed, as well as the hydrofluorate of fluoride, were absolutely free from chlorine.
The gas obtained in our experiments is therefore either fluorine or a perfluoride of hydrogen.
New experiments are necessary to settle this last point. We hope soon to lay the results before the Academy.—Comptes Mendus, vol. ciii., p. 202, July 19, 1886; Chem. News.
Comptes Rendus, vol. cii., p. 1543, and Chemical News, vol. liv., p. 36.
COHESION AND COHESION FIGURES.[1]
By WILLIAM ACKROYD, F.I.C.
1. A Law of Solubility.
It is customary to regard cohesion as the force which binds together molecules of the same substance, and in virtue of which the particles of solids and liquids are kept together, and also to speak of the attraction exerted between particles of two different bodies as adhesion. The distinction between cohesion and adhesion is a conventional one. The similarity, if not identity, of the two forces is demonstrated by the fact that while cohesion is exerted between particles of the same body, adhesion is exerted with most force between particles of allied bodies. Generally speaking, organic bodies require organic solvents; inorganic bodies, inorganic solvents. For example, common salt is highly soluble in water, but not in ether, and many fats are soluble in ether, but not in water. So many cases like these will suggest themselves to the chemist that I am justified in making the following generalization: A body will dissolve in a solvent to which it is allied more readily than in one to which it in highly dissimilar. Exceptions to the law undoubtedly exist, but none so striking as the following in support of it, viz., that the metal mercury is the only known true solvent for many metals at the normal temperature.