THE CAUSTIC ALKALIES AND THEIR CARBONATES; POTASH, SODA, AMMONIA. The second division of the class of Corrosives has now to be considered. It contains the Caustic Alkalies, and some of their Salts. Poisoning by any of these agents is rare. POTASH.—This substance, in its caustic state, as found in commerce, is in the form of grey-colored cakes. It has an acrid taste, is soapy to the touch, and very deliquescent. Moulded in cylinders, it is often employed as a caustic (Potassa fusa). In solution (Liquor potassæ) it is strongly alkaline, and imparts a brown stain to black cloth. _Potassium carbonate_ or _Carbonate of Potash_ (Pearlash) is extensively used by laundresses and in the dressing of woollen cloth. It is generally sold in a granular condition, white, inodorous, and strongly alkaline; it is soluble in water, but not in alcohol. CAUSTIC SODA.—This agent resembles potash in its general properties. The _Sodium Carbonate_ or _Carbonate of Soda_ (Soap-lees) bears a similar resemblance to the carbonate of potash, except that it crystallizes easily, and effloresces on exposure to the air. AMMONIA.—When pure, ammonia is a colorless, pungent gas; but it is commonly met with dissolved in water, as the liquor ammoniæ. Its vapor is poisonous, and may prove fatal by producing inflammation of the larynx and trachea, and even of the lungs. A case is recorded of a French boy, æt. six, who killed his younger sister by making her swallow several teaspoonfuls of a solution of ammonia. Other instances have also occurred where the liquor ammoniæ has either been taken in mistake for the aromatic spirit of ammoniæ, or purposely, to destroy life. An instance is recorded by Dr. Taylor, as occurring in the practice of Mr. Hilton, where liquor ammoniæ, given by mistake, caused corrosion of the throat and gullet and obstruction of the bronchial tubes by false membrane. The œsophagus was completely dissolved at its junction with the stomach, and there was an aperture in the anterior wall of that organ such as might have been caused by oil of vitriol. The _Ammonium Carbonate_ or _Carbonate of Ammonia_ (Hartshorn, Smelling Salts) has been used as a poison. It may be distinguished from other salts by its being alkaline, by its entire volatility, and by its pungent odor. A young woman in a state of unconsciousness, was made to swallow a quantity of hartshorn. In an hour there was great pain, sickness, and vomiting of blood. The hæmatemesis continued for some days, and then feebleness and emaciation set in, death occurring in three months. On examination the pylorus was found contracted to the size of a crow-quill, while there was a large cicatrix on the posterior wall of the stomach.