To start a DC arc, two electrode rods are briefly touched together. When pulled slightly apart, the electric current jumps across the open air. This jumping current rips electrons away from nearby gas molecules in the gap.
The ripped molecules form a superheated glowing gas called a plasma. This plasma channel reaches extreme temperatures between 4,000 and 7,000 kelvins. The intense heat instantly melts and vaporizes almost any solid chemical sample.
Once vaporized, the sample’s atoms absorb energy and emit specific colors of light. Scientists read these light patterns to identify which elements are in the sample. A direct current power source provides a very steady and continuous heat level.
However, this constant heat can cause a problem called selective volatilization. Chemicals with low boiling points evaporate and vanish very early during the test. Chemicals with high boiling points melt much later in the heating process. This unequal timing makes it hard to measure exact amounts of each element.