active c h 2 wo 4 2 g in the form of the potassium salt was added followed by dropwise addition at 60 u00b0 c of 100 g 35 h 2 o 2 stabilised by 0 1 of dipicolinic acid the mixture was stirred for 2 hours at 60 65 u00b0 c then 1 hr at 70 80 u00b0 c and then refluxed 2 hours and cooled to give 243 g calcium tartrate 4h 2 o another 20 g of the salt was obtained by precipitation by 22 g ca oh 2 total yield 98 gb 1183449 it is possible to obtain sodium l tartrate by hydrolysing cis epoxysuccinate by an epoxide hydrolase of achromobacter and alcaligenes the cis epoxysuccinate is obtained by catalytic epoxidation of maleic acid after the complete conversion of the sodium cis epoxysuccinate to sodium l tartrate calcium chloride is added the calcium tartrate precipitates and is collected by filtration u s pat no 3 957 579 the retarding of the crystallisation of caso 4 0 5h 2 o in water is of economical and practical importance it enables the craftsman to use the mixture for a longer time and it makes to use of mechanical pumping and applying of plaster practical possible one of the most effective retarders is tartaric acid in alkaline medium in practice tartaric acid crystals and ca oh 2 are mixed in dry form with the gypsum this retards the setting action of plaster significantly the calcium tartrate used was obtained by precipitating l tartaric acid by an equimolar amount.