Looks like the barrel is a total loss, but it might be possible to rebarrel the rifle, finish the stock and have a decent piece. G&H serial number of 2052 (or 2082, hard to read) places date of manufacture about 1950 or 51.
Fire extinguishers contain chemicals that are either acidic or alkaline when mixed with water eg electrical fire extinguishers can contain: Carbon dioxide, Sodium/Potassium bicarbonate and Ammonium phosphate; and kitchen units can contain: Potassium acetate, Potassium carbonate and Potassium citrate