1. n. [Drilling Fluids]
The simplest aldehyde, having the formula HCHO. Formaldehyde is used in aqueous solutions as a preservative. In muds, paraformaldehyde is added to protect against bacterial attack. The formaldehyde test determines the paraformaldehyde (bactericide) content of a drilling fluid by a P-alkalinity titration of a sulfite-oxidized mud filtrate.