Abstract
No classes of salts have more liberally rewarded investigation than the arseniates and the phosphates. Witness the discovery of the extraordinary phosphates of lime by Berzelius ; the observation of the identity of form of the corresponding arseniates and phosphates by Mitscherlich, and the doctrine of isomorphism to which that observation led; the discovery by the same chemist of two biphosphates of soda, agreeing in composition but differing in form; and lastly, the discovery of the pyrophosphates by my friend and townsman Mr. Clark. Much, however, still remains to be done to complete the history of these interesting salts.