In connection with the determination of sulfate S, the sulfur mass bal
ance for four bituminous coals was determined using different extracti
on procedures, including use of 1 M and 4.8 M HCl under nitrogen and u
nder air, and at room temperature, 95 degrees C and boiling point. Sin
ce HCl extractions yielded poor S mass balances (as low as 83%), acid
extraction with formic acid was also evaluated, Extractions with formi
c acid gave better S mass balances than those obtained using HCl, and
the sulfate S yields agreed with those measured by the ASTM D-2492 HCl
procedure. S-34/S-32 ratios determined by stable sulfur isotope mass
spectrometry demonstrated that formic acid extraction was more selecti
ve for sulfate sulfur than the more rigorous HCl extractions.