since when did calcium oxalate become considered a soluble salt?  And you learned chemistry where? http://en.wikipedia.org/wiki/Oxalic_acid " Oxalic acid  is the  chemical compound  with the  formula  C 2 O 2 (OH) 2  or HOOCCOOH. This colourless solid is a relatively strong  carboxylic acid , being about 3,000 times stronger than  acetic