Final answer:
The Griess Test is used to detect nitrates in gunpowder residue by producing a colored dye upon reaction. Metals can be detected via metal detectors or laboratory techniques like AAS and ICP-MS. Gold is tested using a specific acid test involving nitric acid and hydrochloric acid.
Step-by-step explanation:
The test used to check for nitrates in gunpowder residue involves the use of chemicals to detect the presence of nitrate ions. A common method is the Griess Test, which relies on the reaction of nitrates with a series of reagents to produce a colored dye if nitrates are present. This test is used in forensic analysis to detect gunpowder residue on surfaces or suspects. To detect metals, various analytical techniques can be employed, including using a metal detector for field surveys, or more comprehensive methods like atomic absorption spectroscopy (AAS) or inductively coupled plasma mass spectrometry (ICP-MS) for laboratory analysis.
When specifically testing for the presence of gold, a spot test is used. This involves treating the sample with nitric acid, whereby gold does not react or dissolve. Following this, the sample is introduced to a mixture of nitric acid and hydrochloric acid, known as aqua regia, in which gold can dissolve. This method for testing gold originated during the California gold rush and is colloquially referred to as the "acid test", which now denotes a method that has been "tested and approved".