PURPOSE: To increase the detergency of the resulting titled detergent to metallic oxides, to reduce the corrosiveness and to inhibit the deposition of metallic oxalates by combining oxalic acid or a slat thereof with an Al salt.

CONSTITUTION: The titled detergent contains oxalic acid or a salt thereof and an Al salt. The preferred salt of oxalic acid is the Na salt, K salt, Li salt, Al salt, NH4 salt or hydrazine salt. The preferred Al salt is Al sulfate, oxalate, citrate or chloride. The detergent is used to deterge a boiler plant, a cooling water system, etc., contaminated by metallic oxides.