constituents of coal-tar. It forms yellowish-red prismatic crystals, nearly insoluble in cold, but dissolved to a small extent by boiling water, and readily soluble in alcohol and ether. It possesses exceedingly strong tinctorial powers.
Al′kahest, the so-called universal solvent or menstruum of the alchemists. The word is believed to have been invented by Paracelsus.
Al′kali (from Ar. al-qali, the ashes of the plant from which soda was first obtained, or the plant itself), a term first used to designate the soluble parts of the ashes of plants, especially of seaweed, and designated fixed alkali, as marking a distinction from ammonia, which was termed volatile alkali. Now the term is applied to various classes of bodies having the following properties in common: (1) solubility in water; (2) the power of neutralizing acids, and forming salts with them; (3) the property of corroding animal and vegetable substances; (4) the property of altering the tint of many colouring matters—thus, they turn litmus, reddened by an acid, into blue; turmeric, brown; and syrup of violets and infusion of red cabbages, green. The alkalies may be regarded as water in which part of the hydrogen is replaced by a metallic radicle. The caustic alkalies are strong alkalies which have a powerful corrosive action on the skin, and the common ones are potassic hydroxide or caustic potash, sodic hydroxide or caustic soda, and lithic hydroxide. Volatile Alkali, or ammonic hydroxide, is a much feebler alkali than the others, and when the solution is heated all the ammonia is driven off. Other alkalies are calcic hydroxide or slaked lime, a solution of which in water is known as lime-water; baric hydroxide and strontic hydroxide, derived from the metals barium and strontium. Quicklime is the only alkali extensively used in agriculture.
Alkalim′eter, an instrument for ascertaining the quantity of free alkali in any impure specimen, as in the potashes of commerce. These, besides the carbonate of potash, of which they principally consist, usually contain a portion of foreign salts, as sulphate and chloride of potassium, and as the true worth of the substance, or price for which it ought to sell, depends entirely on the quantity of carbonate, it is of importance to be able to measure it accurately by some easy process. This process depends on the neutralization of the alkali by an acid of known strength, the point of neutralization being determined by the fact that neutral liquids are without action on either red or blue litmus solution. The alkalimeter is merely a graduated tube—a burette—with a stopcock at the lower extremity, from which the standard acid is dropped into water in which a known weight of the substance is dissolved. The quantity required to produce neutralization being noted, the strength of the liquid tested is easily arrived at. A process of neutralization, exactly the same in principle, may be employed to test the strength of acids by alkalies, the one process being called alkalimetry the other acidimetry.
Al′kaloid, a term applied to a class of nitrogenous compounds having basic properties, found in living plants, usually in combination with organic acids. They are usually given names ending in -ine, as morphine, quinine, aconitine, nicotine, caffeine, &c. Most alkaloids occur in plants, but some are formed by decomposition. Most natural alkaloids contain carbon, hydrogen, nitrogen, and oxygen, but a few contain no oxygen. The nitrogen they contain imparts to them basic properties—they are organic bases—and hence they all form salts with acids. They all possess a pronounced bitter taste, and the poisonous nature of many plants, e.g. hemlock, yew, deadly nightshade, &c., are due to the alkaloids they contain. Although formed originally within the plant, it has been found possible to prepare several of these alkaloids by artificial means.
Al′kanet, a dyeing drug, the bark of the root of the Anchūsa or Alkanna tinctoria, a plant of the order Boraginaceæ, with downy and spear-shaped leaves, and clusters of small purple or reddish flowers. The plant is sometimes cultivated in Britain, chiefly on the east coast of England, but most of the alkanet of commerce is imported from the Levant or from southern France. It imparts a fine deep-red colour to all unctuous substances and is used for colouring oils, plasters, lip-salve, confections, &c.; also in compositions for rubbing and giving colour to mahogany furniture, and to colour spurious port-wine.
Alkan′na, a name of henna. See also Alkanet.
Alkar′sin, an extremely poisonous liquid containing kakodyle, together with oxidation products of this substance, and formerly known as Cadet's fuming liquor, characterized by its insupportable smell and high degree of spontaneous combustibility when exposed to air.
Al-katif, a town of Arabia, on the Persian Gulf, carrying on a considerable trade. Pop. 6000.
Alkmaar (a˙lk′mär), a town of the Netherlands, province of North Holland, on the North Holland Canal, and 20 miles N.N.W. of Amsterdam; regularly built, with a fine church (St. Lawrence) and a richly decorated Gothic town-house; manufactures of salt, sail-cloth, vinegar, leather, &c., and an extensive trade in cattle, corn, butter, and cheese. Pop. 22,685.