Common Name: Oxalic Acid, Hydrogen Oxalate, Sorrel Acid  Causes & Symptoms for Dr. Reckeweg Acidum Oxalicum It is indicated in patients with excruciating pains, which is aggravted by thinking of it. Excruciating agony in back, chest, stomach, and abdomen is relieved with Oxalic Acid. Coldness of surface, numbness, mottled skin, blue nails are leading notes for the use of Acidum Oxalicum