(UK Und.) aqua fortis, nitric acid when used to test for gold.
|Cockney Cavalcade 120: ‘Try the acky on it if you like. There y’are,’ he went on, putting the acid on the table, together with a file.|
|Inside the Und. 45: The ‘acky’ trick – you know, switching the jar of nitric acid ‘aqua fortis’ [...] for another.|