Benzidine test detects -

Ref: THE ESSENTIALS OF FORENSIC MEDICINE AND TOXICOLOGY- Dr. K.S.NARAYAN REDDY 32 EDITION page no-430 The chemical test depend on the presence in the blood stains of an enzyme peroxidase ,which in the presence of H2O2, oxidises the active ingredient of the reagent and produces the characteristic coloured compound. Cut out a small piece of stained material or tease out fibres from the stained fabric and place it on procelain tile. Add a drop of saturated solution of benzidine in a glacial acetic acid , and then a drop of 10 volumes hydrogen peroxide.If the blood is present, dark blue colour is produced immediatly. A positive reaction is given by blodd of almost any age, blood that has been exposed to heat or cold , and the blood stains treated with cleaning agents. it is the best preliminary test for blood and it detects blood when present in a dilutoon of one pa of blood in 3 lakhs. Positive reaction is not proof of presence of blood , but a negative reaction rules out of the presence of blood. A weaker reaction is otained from ceain other substances, eg.salive,pus,milk,rust,formalin,ceain vegetables and animal juices , oxidising agents , bacteria etc..