and m1 is hydrogen an alkali metal or ammonium or a radical of the formula ch 2 q ox where q is 2 5 and x is hydrogen or a hydrocarbon radical having from 1 to 8 carbon atoms or a radical of the formula ch 2 r n ch 2 s coom2 2 where r and s which may be the same or different are each 2 5 and m2 is hydrogen an alkali metal or ammonium alternatively both r2 and r3 may be replaced by a radical of the formula ch 2 t o ch 2 t where t is 2 5 the amount of the reagent used is preferably in the range from 0 01 to 15 preferably from 0 5 to 10 based on the weight of dry calcium oxide in order to produce calcium carbonate in the scalenohedral form the quicklime is preferably added to sufficient of the aqueous medium to give on completion of step a a suspension having a calcium hydroxide concentration of from 0 7m to 4m 5 30 w v the temperature of the aqueous medium is preferably maintained in the range from 30 u00b0 to 50 u00b0 c and the aqueous medium is preferably subjected to substantially continuous agitation during the slaking step the duration of the slaking step is conveniently in the range from 15 to 30 minutes on completion of the slaking step the suspension is preferably poured through a sieve of aperture size in the range from 40 to 70 microns in order to remove unslaked lime and other undesirable impurities in step b in order to produce calcium carbonate in the scalenohedral form the suspension of slaked lime is preferably diluted if necessary to a concentration of not.