The primary purpose of ASTM D5705 is to determine the vapor phase concentration of hydrogen sulfide (H₂S) in crude oil. This is distinct from measuring total sulfur content; this test specifically looks at the dangerous gas that accumulates in the air space above the liquid oil.

The precision of this measurement depends on the "Henry’s Law" relationship, where the amount of dissolved gas in the liquid is proportional to its partial pressure in the gas phase above it. 5. Significance and Safety : H2Scap H sub 2 cap S

in the liquid phase to reach equilibrium with the vapor phase in the headspace.