He developed ideas on the attractive and repulsive forces involved in chemical affinity, which later had influence on his successors William Cullen and Joseph Black. He compounded "Plummer's pills", a mixture of calomel and antimony sulfide with guaiacum; the pills were originally compounded to treat psoriasis but were used for more than a century as an antisyphilitic.
He conceived notions about attractive and repulsive forces in chemical affinity, which subsequently impacted his successors William Cullen and Joseph Black. He formulated "Plummer's pills," a blend of calomel and antimony sulfide with guaiacum; the pills were initially created to treat psoriasis but were utilized for over a century as an antisyphilitic.