The intercalation of sodium-potassium alloys into graphite leads, at room temperature, to compounds close to KC8. Graphite powder fits to large amounts of the alloy : up to compositions close to MC2, but the stable state is a mixture of KC8 and alloy excess. In spite of the presence of large quantities of free alloy, liquid at room temperature, the powder does not agglomerate and constitutes an important solid reservoir for alkali metals.