Need to find an obscure chemical property? An important formerly print resource for “..physical, thermodynamic, mechanical, and other key properties…”, the International Critical Tables of Numerical Data, Physics, Chemistry and Technology, is available online for free from Knovel. “In 2003, Knovel undertook the conversion of this publication into full-text searchable electronic format that makes data easily accessible. 7 most important tables were made interactive for increased searchability and user-friendliness.”
You can access it through the link in my research guide, along with links to several other free and subscribed resources for chemical properties and spectra.