Methylene Blue Dye
Concentrated dye powder used for staining DNA.
Dilute with 4 liters (or a gallon) of water to make
a strong dark dye.
Used for staining microscope speciments to show the
nucleus, or to stain DNA in gel electrophoresis to
show the banding (DNA fingerprinting, or DNA barcoding).
Also has fun uses in chemistry as a dissolved oxygen indicator.