consisted of electro-negative sulphur trioxide (SO3) in combination with electro-positive oxide of potassium (K2O); while each of these proximate constituents of potassium sulphate were themselves composed of the electro-negative oxygen in combination with electro-positive sulphur, or potassium. On contrasting sulphur with potassium, however, the former was considered more electro-negative than the latter; so that the group SO3 as a whole was electro-negative, while K2O was electro-positive. The symbols given above, which are still in universal use, were also devised by Berzelius for the purpose of illustrating and emphasizing his views. These views, however, met with little acceptance at the time in England. Lavoisier’s idea, that oxygen was the necessary constituent of all acids, began about this time to lose ground. For Davy had proved the elementary nature of chlorine; and hydrochloric acid, one of the strongest, was thus seen to contain no oxygen, and Davy expressed the view, founded on his observation, that iodic “acid,” I2O5, was devoid of acid properties until dissolved in water, and that the essential constituent of all acids was hydrogen, not oxygen. The bearing of this theory on the dualistic theory is, that while, _e.g._, sulphuric acid was regarded by Berzelius as SO3, containing no hydrogen, and was supposed to be separated as such at the positive pole of a battery, Davy’s suggestion led to the opposite conclusion that the formula of sulphuric acid is H2SO4, and that by the current it is resolved into H2 and SO4. Faraday’s electrolytic law, that when a current is passed through electrolytes in solution the elements are liberated in quantities proportional to their equivalents, led to the abandonment of the dualistic theory. For when a current is passed in succession through acidified water, fused lead chloride, and a solution of potassium sulphate, the quantities of hydrogen and oxygen from the water, of lead and chlorine from the lead chloride, and the potassium of the sulphate are in accordance with Faraday’s law. But in addition to the potassium there is liberated at the same pole an equivalent of hydrogen. Now, if Berzelius’s theory be true, the products should be SO3 and K2O, but if the opposite view be correct, then K2 is liberated first and by its subsequent action on water it yields potash and its equivalent of hydrogen. This was pointed out first by Daniell, professor at King’s College, London, and it was regarded as a powerful argument against Berzelius’s system. In 1833, too, Graham investigated the phosphoric acids, and prepared the salts of three, to which he gave the names, _ortho-_, _pyro-_, and _meta-_ phosphoric acids. To understand the bearing of this on the doctrine of dualism it must be remembered that P2O5, pentoxide of phosphorus, was at that date named phosphoric acid. When dissolved in water it reacts with bases, forming salts—the phosphates. But the quantity of water necessary was not then