https://chemwatch.net/blog/marquis-reagent/
Marquis reagent - Chemwatch
a solution of formaldehyde in sulfuric acid used in color tests for formaldehyde.
marquis reagentchemwatch
https://bunkpolice.com/marquis-color-guide-reaction-booklet/
Marquis Reagent Color Chart Booklet
marquis reagentcolor chartbooklet