Process for the production of low molecular weight polyhydroxyl compounds

In a process for the production of low molecular weight polyhydroxyl compounds by condensing formaldehyde hydrate in the presence of calcium hydroxide as catalyst and in the presence of compounds capable of enediol formation as co-catalyst, the improvement which comprises adjusting a formaldehyde-containing solution of the co-catalyst in water to a pH value of from 9 to 12 by the addition of calcium hydroxide at a temperature of from 80.degree. to 110.degree. C. so that condensation of the formaldehyde hydrate is started, and then adding to this reaction mixture, (1) an aqueous formalin solution and/or paraformaldehyde dispersion containing from 20 to 65%, by weight, of formaldehyde, and (2) calcium hydroxide at such a rate that the reaction mixture is maintained at a pH value of from 7.5 to 9.5 at a temperature of from 80.degree. to 110.degree. C., the concentration of formaldehyde being maintained at from 0.5 to 10%, by weight, based on the total reaction mixture, throughout the condensation reaction.