First, a blue nitrous acid solution is made by diluting 30 mL of conc. HCl with 50 mL of water and combining it with 18 g of potassium nitrite dissolved in 30 mL of water. The nitrous acid solution in a beaker is immersed in an ice bath until the temperature is below 0°C. Then a fast addition of 7 g of hexamine dissolved in 50 mL of water is started.
The both solutions
While combining the solutions, some foam formed
The mixture, after the addition
Filtering the mixture
The crude product
The recrystallized pure product