water in water step by step addn. of CaCN2 to cold water under stirring; after 2 h filtration; neutralization with H2SO4; filtration of CaSO4;; washing; evaporation at a max. of 80°C to concn. of ca 375 g H2CN2/l; aq. soln. contains small amts. of (CN2H2)2 and urea;;
参考文献
Industrial and Engineering Chemistry, , vol. 16, p. 848 - 852