Which fixative contains formaldehyde and mercuric chloride but not potassium dichromate?

• A. B-5
• B. Helly
• C. Bouin
• D. Gendre

Answer: (A)

Think about fixatives by what they’re made of. The question asks for a fixative that has both formaldehyde and mercuric chloride, but does not contain potassium dichromate. The fixative known as B-5 fits exactly: it’s formulated with formaldehyde (formalin) and mercuric chloride and, in standard recipes, does not include potassium dichromate. This combination gives strong cross-linking and good nuclear detail without introducing chromate compounds.

Bouin’s uses formaldehyde along with picric acid (and acetic acid) and does not include mercuric chloride, so it misses the mercury component. The other listed fixatives have different additive profiles that do not match all three criteria simultaneously.