"All that's solid melts in air."

Posted by Nancy Wilson on July 18, 2006

The phrase is "All that's solid melts in air."
My brother has asked me to determine its origin. Google has no references.
Somebody wrote it in a letter to him, noting that it was from Karl Marx ("of course").
My brother had a feeling it was from Shakespeare / "The Tempest", but looked and did not immediately find it. Nor could he find in what context Marx said it - if he did.
Can anyone help us sort this out? Thanks!

• The Communist Manifesto RRC 18/July/06
  • The Communist Manifesto Victoria S Dennis 18/July/06
    • The Communist Manifesto Constantino 01/August/06