This subject has occupied a dominant position in physico-chemical research since the investigations of van't Hoff and Arrhenius.
This is shown in the case of the chloracetic acids: According to van 't Hoff the substitution of chlorine atoms into a methyl group occasions the following increments: The introduction of chlorine, however, may involve a fall in the boiling-point, as is recorded by Henry in the case of the chlorinated acetonitriles: NC CH 3.
Van't Hoff, Lectures on Theoretical and Physical Chemistry; J.
Van Hoff pointed out that measurements of osmotic pressure confirmed this value in the case of dilute solutions of cane sugar.
This influence extended from Germany to Denmark, where it was embraced by Hoff ding, and to England, where it was accepted by Romanes, and in a more qualified manner as " a working hypothesis " by Stout.