(_a_) _Carbonic acid; or water saturated with the gas._ This will not produce any[331] disturbance in the solution of potass; a fact which at once serves to distinguish this alkali from the earths, _baryta_ and _lime_. (_b_) _Deuto-muriate of Platina_ occasions a canary-yellow precipitate, consisting of the deutoxide of platina, potass, and muriatic acid; as this precipitate is, to a certain extent, soluble in water, the test may fail through dilution. With soda, this reagent will not occasion any precipitate, a fact which depends upon the solubility of the triple salt formed, and affords an easy method of distinguishing the fixed alkalies from each other. (_c_) _Tartaric acid._ If an excess of this acid be added, we shall obtain crystals of a _bi-tartrate_; a phenomenon which will not take place if soda be the alkali employed. _Potassa Fusa_, or _Kali Causticum_. This substance, which occurs in sticks, or cylinders, is an extremely caustic and deliquescent substance; it is principally employed in surgery, to establish an ulcer; or, instead of incision, to open a tumour. See _Pharmacologia_. As it differs from potass, only in the degree of purity, it is unnecessary to offer any farther remarks. _Potassa cum Calce._ This is a mixture of the preceding substance with lime, which is added with a view to diminish the deliquescent property of the alkali, and thus to render it more manageable as an escharotic. There will be no difficulty in separating these ingredients. Their different solubilities will furnish an easy mode of effecting it to a certain extent, and we may then precipitate the remaining portion of lime, by carbonic acid. _Sub-carbonate of Potass_—_Salt of Tartar_—_Pearl-ash_—_Potash_. Although potass becomes comparatively mild, by its union with carbonic acid; yet the present preparation retains so much causticity as to render it poisonous, if administered in any considerable dose. _Plenck_ reports a case of this kind, where a patient having swallowed an ounce of _salt of tartar_, was shortly afterwards seized with a violent vomiting, which continued for forty-eight hours, followed by a violent inflammation of the stomach; from which, however, he ultimately recovered. _Symptoms of Poisoning by any of the above preparations of Potass._