To
500 cc. (Note 1) of concentrated sulfuric acid (sp. gr. 1.84), previously cooled in a freezing mixture, is added, in small portions and with hand stirring,
560 g. of crude (Note 2) guanidine nitrate (obtained from 210 g. of dicyanodiamide as described on p. 302). The temperature is not allowed to rise above 20° during the addition. When all has been added, the milky mixture is allowed to stand at room temperature with occasional stirring until it is homogeneous and free from crystals (Note
3). It is then poured with stirring into 6 l. of a mixture of cracked ice and water. The precipitated
nitroguanidine is filtered, washed free from acid, and recrystallized from the least possible amount (4–5 l.) of boiling water (Note
4). The yield (Note
5) is
380–390 g. (
73–75 per cent of the theoretical amount, based on the
dicyanodiamide used). The product melts with decomposition at about
232° (Note
6).