Potass is rarely met with in a pure form, except in the laboratory of the philosophical chemist, and is therefore not likely to become an object of judicial enquiry; but in various states of mixture, as presented in the different preparations above enumerated, it may become the accidental, as well as criminal means of poisoning; we shall therefore consider the chemical history of these different preparations separately, and then describe the symptoms which they generally occasion.
Liquor Potassæ.
This may be considered as a nearly pure solution of potass, although, as it is usually prepared, it contains small portions of muriate and sulphate of potass, silica, and lime. It is a limpid, dense, colourless solution; when rubbed between the fingers it feels soapy, in consequence of a partial solution of the cuticle. As it constitutes a medicine in common use, and, moreover, forms the basis of many quack medicines, as well as of those preparations which are sold under the name of Depilatories, it may readily become the accidental instrument of mischief.
Chemical Tests for its detection.
There cannot exist any difficulty in this investigation; its highly alkaline characters will be immediately announced by its effects on the vegetable test papers, and by its power of saturating acids; while the particular species of alkali may be readily identified by the following reagents.
(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.