The Collaborative International Dictionary of English v.0.48:

Helianthin \He`li*an"thin\, n. [Prob. fr. L. helianthes, or NL.
   helianthus, sunflower, in allusion to its color.] (Chem.)
   An artificial, orange dyestuff, analogous to tropaolin, and
   like it used as an indicator in alkalimetry; -- called also
   methyl orange.
   [1913 Webster]