The Collaborative International Dictionary of English v.0.48:

Chaldron \Chal"dron\, n. [OF. chaldron, F. chaudron kettle. The
   same word as caldron.]
   An English dry measure, being, at London, 36 bushels heaped
   up, or its equivalent weight, and more than twice as much at
   Newcastle. Now used exclusively for coal and coke.
   [1913 Webster]

   Note: In the United States the chaldron is ordinarily 2,940
         lbs, but at New York it is 2,500 lbs. --De Colange.
         [1913 Webster]

WordNet (r) 3.0 (2006):

chaldron
    n 1: a British imperial capacity measure (liquid or dry) equal
         to 36 bushels

Bouvier's Law Dictionary, Revised 6th Ed (1856):

CHALDRON. A measure of capacity, equal to fifty-eight and two-third cubic
feet nearly. Vide Measure.