Solvent Yellow 124

This dye can be easily hydrolyzed with acids, splitting off the acetal group responsible for its solubility in nonpolar solvents, and yielding a water-soluble form which is easy to extract to water.

Like a similar methyl orange dye, it changes color to red in acidic pH.

It can be easily detected in the fuel at levels as low as 0.3 ppm by extraction to a diluted hydrochloric acid, allowing detection of the red diesel added into motor diesel in amounts as low as 2-3%.

Solvent Yellow 124 is intended to be difficult to remove from the fuel in an economical way.

The UK government expressed concerns about the possibility of "laundering" the dye out of "illicit" fuel, hampering the detection.

NFPA 704 four-colored diamond Health 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g. sodium chloride Flammability 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oil Instability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogen Special hazards (white): no code
Solvent Yellow 124, hydrolyzed protonated form
Heating oil detection in Diesel fuel