This International Standard specifies an esterification method for the determination of the hydroxyl number of the following polyglycols for industrial use : - polytethylene glycol) [HO(C2H40)nHl, where y1 is greater than 3; - poly(propylene glycol) [HO(C3H60)nH], where n is greater than 3. The method is not recommended for products containing more than 0,2 % (mlm) of water, unless the Sample is first dried.