How to find out if a link has been published on rhodium.ws before:
load https://www.thevespiary.org/rhodium/Rhodium/chemistry/index.html (https://www.thevespiary.org/rhodium/Rhodium/chemistry/index.html)
look at the source code in a text editor
search for the url in question.
Try that, dear 8ball, before randomly blabbering insults next time.
Just in case this procedure is a little too complex for you, check the link 'Organic Laboratory Instructional Video Clips' in the 'Multimedia' section.