85 

 and Adams (1979) . Several indirect methods of sulfate determination 

 by measuring the removal of Ba, Pb, or Sr from solution by sulfate have 

 been proposed (Roe et al. , 1966; Gersonde, 1968; Dunk at al. , 1969; 

 Borden and McCormick, 1970; Loeppert and Breland, 1972; Hue and Adams, 

 1979) . These methods are comparable to turbidimetry where accuracy 

 and reproducibility are of concern. They also involve difficulties in 

 analysis of the associated cation. The most successful techniques in- 

 volve the indirect measurement of sulfate by Ba precipitation and 

 determination of Ba by atomic absorption spectroscopy. Major difficul- 

 ties associated with this technique are achieving complete precipita- 

 tion of small quantities of sulfate, Ba ionization interferences by 

 atomic absorption, Si and Al interferences with Ba absorption, and 

 organic matter, K, and Ca interferences with BaSO, precipitation 

 (R. H. Loeppert, Jr. 1972. Analysis of sulfate in soil extracts by 

 atomic absorption spectroscopy. Master's thesis. University of 

 Florida, Gainesville). Hue and Adams (1979) improved the technique by 

 seeding samples with BaSO,, by precipitating in 50% ethanol solution to 

 lower BaSO, solubility, by using C1CH.C00H and KOH to control ioniza- 

 tion interferences, and by determining Ba in a N„0/acetylene flame. 

 Their technique was adopted for use in this study on soil ex- 

 tracts with very low concentrations of sulfate or where the presence of 

 color due to Fe or organic matter might present problems with turbidi- 

 metric techniques. Their method is briefly outlined in Appendix D. 



