In recent years, many of the lithium compounds appearing on the market have contained lithium having an atomic weight different from that of natural or virgin lithium, 6.940. The Atomic Energy Commission has been processing lithium compounds for the isolation of the isotope of atomic weight six and has been returning residues to the manufacturers for resale. For most end uses this variation in atomic weight is of no consequence. However, the uncertainty in the atomic weight gives rise to considerable difficulty whenever good analytical work is performed on materials bearing depleted lithium. The lithium compounds sold through GFS have been prepared from virgin lithium hydroxide or equivalent raw materials.