Some years ago I commenced an examination of the behaviour of the so-called olefines towards certain compound halogens. I was induced to this by the conviction that the bodies resulting from the union of a group of unequally chemico-negative elements with an olefine, would place an instrument of great power into the hands of systematic chemists, especially of synthesists. My expectations have been more than realized. The few olefines which I have examined in their relation to compound chemico-negative groups have given rise to a series of new bodies remarkable alike for their great number and for the elegance and importance of the reactions attending their formation and recompositions.