commonly used as a preservative for tissue specimens
Fixation (histology) By far the most commonly used fixative in histology is formaldehyde. It is usually used as a 10% neutral buffered formalin (NBF), that is approx. 3.7%-4.0% formaldehyde in phosphate-buffered saline. Because formaldehyde is a gas at room temperature, formalin-formaldehyde gas dissolved in water (~37% w/v) is used when making the former fixative. Paraformaldehyde is a polymerized form of formaldehyde, usually obtained as a fine white powder, which depolymerises back to formalin when heated. Formaldehyde fixes tissue by cross-linking the proteins, primarily the residues of the basic amino acid lysine. Its effects are reversible by excess water and it avoids formalin pigmentation. Other benefits include: Long term storage and good tissue penetration. It is particularly good for immunohistochemistry techniques. Also the formaldehyde vapor can be used as a fixative for cell smears.
Benedict's reagent It is a complex mixture of sodium carbonate, sodium citrate and copper(II) sulfate pentahydrate.[2] It is often used in place of Fehling's solution to detect the presence of reducing sugars. The presence of other reducing substances also gives a positive reaction.[3] Such tests that use this reagent are called the Benedict's tests. A positive test with Benedict's reagent is shown by a color change from clear blue to a brick-red precipitate.