The invention relates to linear carboxy-functional organosiloxane compounds of the general formula (I) ##STR1##

in which

a is from 1 to 200,

R¹ are identical or different aliphatic or aromatic hydrocarbon radicals and

R² is —(Y)[O(C₂H_4-b(R³)_bO)_c(C_dH_2dO)_e]_fX,

and the use thereof for the treatment of the surface of leather.