The Collaborative International Dictionary of English v.0.48:

Calx \Calx\, n.; pl. E. Calxes, L. Calces. [L. Calx, calcis.
   limestone; cf. Gr. ? gravel. ?, ?, pebble, Skr. ? gravel, Ir.
   carraic rock Gael. carraig, W. careg, stone. Cf. Chalk.]
   [1913 Webster]
   1. (Chem.)
      (a) Quicklime. [Obs.]
      (b) The substance which remains when a metal or mineral
          has been subjected to calcination or combustion by
          heat, and which is, or may be, reduced to a fine
          powder.
          [1913 Webster]

   Note: Metallic calxes are now called oxides.
         [1913 Webster]

   2. Broken and refuse glass, returned to the post.