This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
By mixing 3 parts of nitric, with 4 of hydrochloric acid, and afterward 25 of distilled water: the strong acids, undiluted, are left to act upon each other for twenty-four hours to insure complete decomposition and the full development of free chlorine.
2HNO3 + 6HC1 = 4H1O + 2NO + 3C12
At the same time two other compounds are formed - chloro-nitrous and chloro-nitric gas. If the acids be diluted before being mixed, the same reaction occurs, but requires several days for completion.