Potash is one of those medicines which have several distinct actions; but its various operations are comparatively simple in nature, and easy to comprehend. In the solid state it is powerfully caustic and corrosive, having a great affinity for water, and abstracting it from the animal tissues with which it is brought in contact. When a dose of the solution, properly diluted with water, is administered internally, it passes first into the stomach, and either combines with the acid of the gastric juice, or, what is more probable, it becomes absorbed too rapidly to be neutralized by it. It passes then into the blood, and probably exists in that liquid in a free state, for the blood already contains a slight excess of alkali. However this may be, it certainly increases the amount of alkali in the system. Its hæmatic action depends in great part on its power of neutralizing acidity. It is thus useful in cases of acid dyspepsia, heartburn, or gastrodynia, when it combines with the excess of acid which exists in the gastric secretion, and probably also in the blood. For the same reason it is useful in some cutaneous diseases that are connected with disordered digestion. It is employed in Gout and Rheumatism, where there is obviously an excess of acid both in the blood and in the secretions. (p. 202.) When Potash, is administered in any quantity, it must be excreted from the blood. The secretion of alkalies is mainly performed by the kidneys, and by their agency we may render the urine neutral or alkaline, and thus counteract a tendency to lithic deposits. (_Vide_ Solvents.) For this purpose Potash is preferable to free Soda, for the lithate of Soda is comparatively an insoluble salt. The salts of Potash with vegetable acids change into carbonates while in the blood, and will render the urine alkaline. M. Wöhler, who has discovered this fact, finds that it does not occur with the super-salts. Even the neutral salts escape the oxidation when they are given in such large doses as to act on the bowels. Potash is thus a Restorative Hæmatic, and where, from any reason, alkaline matter is needed in the system, it directly supplies the want. But it has also other actions which render it Catalytic, and which are evidenced in disorders in which there is no such deficiency of alkali. By dissolving Fibrine, it tends to prevent its deposition from the blood. It thus interferes with the inflammatory process, and acts as a general Antiphlogistic. It is possibly by a similar action that it seems able to counteract the deposit of crude tubercle, and exerts a special action in the prevention and cure of strumous disorders. It is very useful in the early stage of Phthisis, and in all stages of Scrofula. In Syphilis, when occurring in scrofulous subjects, Potash has sometimes been used with greater advantage than Mercury.