The percentage of ion-exchangeable cations was determined for the Center lignite. The ion-exchanged material was produced by treating the lignite with ammonium acetate which upon heating yields hydrogen attached to carboxyl groups. The amount of exchangeable sodium was found to be 95 percent while the amount of exchangeable calcium was 46 percent. Adhesive properties of the Center lignite ash were evaluated using the sticking apparatus developed by Abbott, Moza and Austin. The minimum substrate temperature for adherence (sticking temperature) was found to be 375/sup 0/C for Center ash. The adhesive strength of the slag to the substrate increased almost logarithmically when the substrate temperature was increased in the range up to 525/sup 0/C. A vertical tube furnace was used to grow deposits on cooled boiler steel substrates, providing a means to gain knowledge as to coal specific behavior related to ash deposition. The rate of ash deposition was measured with regard to ion-exchanged coals and hot zone temperature. The effect of removing the ion-exchangeable cations from Center lignite did not significantly change the rate of deposition. The strength of the deposits formed from the ion-exchangeable Center were markedly reduced as compared to the Center lignite due to decreased availability to alkali and alkaline earth elements which may be responsible for liquid phase sintering of the ash. The crystalline species consisted of anorthite and pyroxene with minor and trace amounts of gehlenite. Hot zone temperature had no effect on deposition rates for Center or ion-exchanged Center lignite, but the deposits formed from combustion in a hot zone temperature of 1500/sup 0/C had greater strengths than at 1400/sup 0/C. In the ion-exchanged coals the deposit strength was weaker at a hot zone temperature 1400/sup 0/C as compared to 1500/sup 0/C.