The mandelin reagent is used for testing a number of substances but has higher toxicity and is generally made less useful by the availability of the froehde and liebermann reagents. It is offered as a specialist product- for most people we recommend getting one of the multipacks instead.
The mandelin reagent can detect the presence of PMA and PMMA, which it gives a reddish-brown reaction for.
The mandelin reagent begins life as a reddish liquid but within about 48 hours it develops a brilliant-yellow colour. This is normal and will not interfere with results.