1. J. Reinhard, W.E. Stump and J.S. Davidson, U.S. Pat. 3,767,489 (1973).
2. E. Edward, S. Gorden and S.H. Hayes, Br. Pat. 1,423,337 (1976).
3. Nitrochemie GmbH, Br. Pat. 1,498,171 (1978).
4. Nitrochemie GmbH, Br. Pat. 1,498,172 (1978).
5. J.S. Stack, U.S. Pat. 3,954,667 (1976).