The Collaborative International Dictionary of English v.0.48:

Petrolatum \Pet`ro*la"tum\, n. (Chem. & Pharm.)
   A semisolid unctuous substance, neutral, and without taste or
   odor, derived from petroleum by distilling off the lighter
   portions and purifying the residue. It is a yellowish,
   fatlike mass, transparent in thin layers, and somewhat
   fluorescent. It is used as a bland protective dressing, and
   as a substitute for fatty materials in ointments. --U. S.
   Pharm.
   [1913 Webster]

   Note: Petrolatum is the official name for the purified
         product. Cosmoline and vaseline are commercial
         names for substances essentially the same, but
         differing slightly in appearance and consistency or
         fusibility.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Cosmoline \Cos"mo*line\ (k?z"m?-l?n), n. [Prob. fr. cosmetic +
   L. oleum oil.] (Chem.)
   A substance obtained from the residues of the distillation of
   petroleum, essentially the same as vaseline, but of somewhat
   stiffer consistency, and consisting of a mixture of the
   higher paraffines; a kind of petroleum jelly.
   [1913 Webster]