Benzaldehyde is also a precursor to certain acridine dyes. Chlorophyllin also binds to acridine orange. Acridine and its homologues are weakly basic. Cell apoptosis is tested by treating the lysosomal membrane with acridine orange. Examples include ethidium bromide and acridine. Several dyes and drugs feature the acridine skeleton. The carbon 9-position of acridine is activated for addition reactions. Acridine and its derivatives can be prepared by many synthetic processes. Acridine is easily oxidized by peroxymonosulfuric acid to the acridine amine oxide. Acridine orange is derived from dimethylaminobenzaldehyde and "N","N"-dimethyl-1,3-diaminobenzene. Acridine dyes are prepared by condensation of 1,3-diaminobenzene derivatives. Acridine orange is used in epifluorescence microscopy and flow cytometry. Addition of potassium dichromate to this solution precipitates acridine bichromate. When formic acid is the carboxylic acid, the reaction yields the parent acridine. There are no commercial applications of acridines but at one time acridine dyes were popular.