The general term Alkali comprehends under it substances possessed of very important chemical properties, and capable of producing very powerful effects on the animal economy. Alkalies have an acrid, or pungent, urinous taste; are caustic, or dissolve animal matter; change the blue vegetable colours to green; serve in some instances as the means of combining oil and water; are capable of being fused and volatilized by a strong heat; have a great affinity for water; and combine with acids, forming neutral salts, in which the qualities of both the components are lost. All of them, however, do not display these properties; and therefore the term alkali is now proposed to be confined to those substances "which form definite compounds with acids, and which when liquid have an alkaline

The words Kali and Alkali are of Persian origin, and derived from the terms

and or Kalla and Alkalixi, signifying the ashes of marine plants.

Vide Good's Nosology, Prelim. Disc. p. xcv. The Rev. W. Palmer, the professor of Arabic at Cambridge, gives the following as the origin of the term.

"From the Arabic root (Kala), to dress any thing by fire, is derived the substantive (Kilyon), the ashes produced by burning the Sarlicornia or any other plant of the same nature. Hence Kali, with the article Al-lali."

2 The title of this section in the London Pharmacopoeia is Alkalies and their Salts; but as these salts cannot be termed Salts of Alkalies, in strict language, we formerly translated the phrase neutral salts; but, as this term applies also to salts in which there is no excess either of acid or of alkalies, we, therefore, have adopted the simple term salts.

re-action1" The discoveries of Sir H. Davy have clearly established that potassa, soda, lime, and magnesia are compound bodies, with metallic bases. They are affected by the air, and require to be preserved in well-stopped glass bottles. The alkalies, in reference to their chemical properties, may be arranged nearly in the same manner as .the acids.

II. Alkalies Composed Of A Simple Radical With Hydrogen. Nitrogen + Hydrogen 1. Ammonia

Of these potassa, soda, lime, and ammonia, only, are employed in an uncombined state in pharmacy.

Neutral Salts, strictly speaking, have neither acid nor alkaline properties: but salts exist, formed by the combination of acids with alkalies, in which the properties of the one or the other predominate; and, consequently, although these are secondary salts, yet they cannot, in strict language, be denominated neutral salts. When the acid predominates, the salt is designated by the syllables hi or super being added to the appellation of the neutral salt, formed with the same acid and alkali; but when the alkali is redundant, the syllable sub is added; thus, if to carbonate of potassa be added a quantity of acid equal to that which it already contained, it becomes a Bicarbonate or a Supercarbonate of Potassa; but if there be less acid than in the neutral carbonate, the salt is a Subcarbonate of Potassa. The term super, however, is too indefinite, as some alkalies form more than one super salt. The British Pharmacopoeias still use the term oxy in reference to acids; when the acidifying base, therefore, contains a maximum of oxygen, the syllable ate is prefixed to that of the salt; thus, sulphate of potassa denotes a salt composed of the sulphuric acid and potassa: when an alkali is united with an acid with a minimum of oxygen, the salt formed has the term ite prefixed to it; thus, sulphite of potassa.

The first is salt formed by sulphuric acid and potassa, the second of sulphurous acid and the same alkali.

1 Turner's Elements, 4th edit. p. 630.

The neutral and secondary salts have very different degrees of solubility : but that of almost all of them is increased by an augmented temperature, while the solution is, for the most part, accompanied with a diminution of temperature. The same quantity will dissolve several different salts, which do not decompose one another. They may be obtained unaltered from solutions by evaporation; and if the process be slowly conducted, they form in regular crystallized masses, which have more or less transparency according to the quantity of water which they retain in their composition. A salt may contain half its weight of water, and yet appear dry. Exposure to air, heat, and moisture, variously affect the appearance of crystallized salts. When they lose their transparency and are covered with a white crust, or fall to powder on simple exposure to the air, such salts are said to effloresce; if, on the contrary, they attract moisture from the atmosphere, and become fluid, they are said to deliquesce; and they are permanent, when the air has no effect on their crystals.

The circumstance of a salt first melting in a moderate heat, then becoming covered with a white crust, and ultimately being converted into a dry opaque mass, is termed watery fusion; but when, instead of melting, it splits, and the fragments fly off with a crackling noise, this effect is termed decrepitation. The first contain much water, the second are generally devoid of water.

The efflorescent and deliquescent salts should be preserved and dispensed in well-stopped bottles; while those that are permanent will not suffer from being put up in paper.

The alkalies have been employed as poisons; in which case the practitioner ought to be able to distinguish them from other acrid or caustic poisons. The volatile alkali is readily known by its odour; but if any of the fixed alkalies have been taken, besides the characters already enumerated, and which merely demonstrate the fact that the poison has been an alkali, the simplest method of ascertaining which of the alkalies is the poison in question, is to evaporate the solution, or some of the filtered fluid contents of the stomach, till it is concentrated, and then add a solution of chloride of platinum: if a yellow precipitate fall, the alkali is potassa; or if it be a simple aqueous solution, evaporate to dryness in a silver spoon or vessel: after which, by exposing the mass to the air, if the alkali be potassa it will rapidly deliquesce, but it will remain dry if it be soda. Vinegar is the best antidote of the alkaline poisons, when given early enough after the poison has been swallowed.