1.The acids CCl3(CH2)11COOH (n = 2–6) and CCl2=CH-(CH2)11) (n = 1–6) have been prepared, and their dissociation constants have been measured potentiometrically.2.It has been found that the CCl3and CCl2=CH groups have appreciable effects on the dissociation constants of the acids, there effects fall off regularly as the length of the chain separating these groups from carboxyl increases.3.It has been found that 4,4-dichloro-3-butenoic acid has a higher dissociation constant that 4,4,4-trichlorobutyric acid, whereas in the succeeding acids in the two series the reverse relationship holds4.It has been found that in the higher ω,ω,ω-trihalo carboxylic acids, the CCl3and CF3groups have approximately the same effect on the dissociation co