residue vs scum

residue

noun
  • The substance that remains after evaporation, distillation, filtration or any similar process. 

  • A molecule that is released from a polymer after bonds between neighbouring monomers are broken, such as an amino acid in a polypeptide chain. 

  • Whatever property or effects are left in an estate after payment of all debts, other charges and deduction of what is specifically bequeathed by the testator. 

  • Whatever remains after something else has been removed. 

  • A form of complex number, proportional to the contour integral of a meromorphic function along a path enclosing one of its singularities. 

scum

noun
  • A layer of impurities that accumulates at the surface of a liquid (especially molten metal or water). 

  • Semen. 

  • A greenish water vegetation (such as algae), usually found floating on the surface of ponds 

  • A reprehensible person or persons. 

  • The topmost liquid layer of a cesspool or septic tank. 

verb
  • To remove (something) as scum. 

  • To startscum or savescum. 

  • To remove the layer of scum from (a liquid etc.). 

  • To become covered with scum. 

How often have the words residue and scum occurred in a corpus of books? (source: Google Ngram Viewer )