Here's why:

* Preservation: Formaldehyde acts as a fixative, preventing decomposition and preserving the tissues for examination. It does this by cross-linking proteins, making them more rigid and resistant to breakdown.

* Disinfection: Formaldehyde is also a powerful disinfectant, killing bacteria and other microorganisms that could cause further decay.

* Appearance: Formaldehyde helps maintain a more natural appearance of the tissues, making it easier for pathologists to examine them.

While formaldehyde is a key component, autopsy chemicals often contain other ingredients as well, such as:

* Buffering agents: These help maintain the pH of the solution.

* Water: Acts as a solvent for the other ingredients.

* Colorants: These can be added to help distinguish between different tissues.

It's important to note that formaldehyde is a hazardous substance and should only be handled by trained professionals.