Dissolve 59 g of mercury(II) nitrate in 1000 ml of water and add enough of nitric acid to prevent a formation of basic salt. Dissolve 30 g of potassium thiocyanate in 100 mL of water and combine the solutions. Filter and wash with 200 mL of water. Dry the product, it hardens.
Hg(NO3)2 + 2 KSCN = Hg(SCN)2 + 2KNO3
Combining the solutions, the product precipitates immediately