dye under certain circumstances the dye will precipitate out from the buffered solution and thus provide a permanent record of the determination the mixture is also stable and unaffected by oxygen of the air or by hydrogen peroxide application_number US 15621088 A description as indicated above the chromogenic substrate to peroxidase enzymes of formula iii is prepared by the reaction of a hydrazone of formula i and a 2 hydroxy 2 4 6 cycloheptatrienone of formula ii in the chromogen substrate r represents a group containing from 1 to 25 and more preferably 1 to 12 carbon atoms and includes an alkyl group e g methyl ethyl n propyl isobutyl n amyl isoamyl and the like an alkenyl group e g allyl methallyl and the like an aralkyl group e g benzyl phenethyl and the like an alkoxyalkyl group e g methoxyethyl ethoxyethyl and the like an aryloxyalkyl group e g phenoxymethyl phenoxyethyl and the like a hydroxyalkyl group e g hydroxymethyl hydroxyethyl betahydroxypropyl and the like a carboxyalkyl group e g carboxymethyl carboxyethyl carboxypropyl and the like a carboalkoxyalkyl group e g carbomethoxymethyl carbomethoxyethyl carboethoxyethyl acetoxyethyl acetoxypropyl and the like an arylthioalkyl group e g phenylmercaptomethyl phenylmercaptoethyl and the like a sulfohylalkyl group e g sulfonic acid butyl and the like r 1 r 4 represent hydrogen halogen no no 2 so 3 h cooh or a group containing from 1 to 25 and more preferably 1 to 12 carbon atoms and can be a substituted or unsubstituted alkyl alkoxy aryl heteroaryl aryloxy and the like x represents.