The Bureau of Mines conducted research to determine the effects of potassium trithiocarbonate (kttc), a degradation product of potassium ethylxanthate (kex), on flotation of chalcopyrite and molybdenite. Small amounts of kttc were identified in fresh and aged solutions of kex using thin-layer chromatography. Hallimond tube flotation tests on pure minerals showed that kttc acts as a weak collector for chalcopyrite. Both kex and kttc tend to depress molybdenite, but the depression effect is easily overcome by addition of a small quantity of fuel oil. The results of the hallimond tube tests were confirmed in batch flotation tests using a porphyry copper ore.