This has confused me too. It seems that if something is soluble in lipid, it wouldn't be soluble in blood. But nitrous is insoluble in both (so works fast but has low potency) and halothane is soluble in both (so works slowly but very potent). So I'm going to try not to overthink it, and just memorize that drugs with high blood solubility will work slowly, and drugs with high lipid solubility will be very potent.