ALKALI, in chemistry, a word applied to all bodies that possess the following properties: they change vegetable blue colours, as that of an infusion of violets, to green : they have an acrid andpeculiar taste : they serve a.s intermedia between oils and water: they are capable of com bining with acids, and of destroying their acidity : they corrode woollen cloth, and, if the solution be sufficiently strong, re duce it to jelly; and they are soluble in water. The alkalies at present known are three ; viz. ammonia, potash, and so da : the two last are called fixed alkalies, because they require a red heat to vola tilize them ; the other is denominated volatile alkali, because it readily assumes a gaseous form, and is dissipated by a very moderate degree of heat Barytes, strontian, lime, and magnesia, have been denominated alkalies by Foumroy : but as they possess the striking character of earths in their fixity, this innovation does not seem entitled to general adoption.
Since writing the above, some discove ries of great importance, on the subject of alkalies, have been made known to the philosophical world by Mr. Davy, Pro fessor of Chemistry at the Royal Institu tion. We shall in this place give a sketch of the two papers which he has just laid before the Royal Society, referring to some subsequent articles for further par ticulars. In a former discourse, read be fore this learned body, Mr. Davy, in speaking of the agehcies of electricity, suggested the probability, that other bo dies not then enumerated might be de composed by the electric fluid. In the course of the last summer, this celebra ted philosopher was employed in making a number of experiments with this par ticular view, and by means of very pow erful galvanic troughs, consisting of a hundred pair of plates, six inches square, and one hundred and fifty pair, four inch es square, he has succeeded in decompo sing potash and soda. A more brilliant discovery has not been made since those which have immortalized the names of Priestley and Cavendish. This was ef fected by placing moistened potash, or soda, on a plate of plating, and exposing it to the galvanic circle. Oxygen was disengaged, and the alkalies reduced to their primitive base, which is found to be a peculiar and highly inflammable mat ter, and which assumes the form and ap pearance of small globules of mercury. These globules are, however, lighter than water, and when potash is used, they are in the proportion of 6 to 10. At the freezing point they are bard and brittle ; and when broken and examined by a mi croscope, they present a number of fa cettes with the appearance of crystalliza tion: at 40° Fahrenheit they are soft, and can scarcely be discriminated but by their gravity from globules of mercury ; at 60° they are fluid, and at the small heat of 100° volatile. When exposed to
the atmosphere, they fapidly imbibe oxy gen, and reassume the alkaline charac ter. In distilled naptha they may be pre served four or five days, but if exposed to the atmosphere, they almost instantly become incrusted with a coat of alkali : the incrustation may be removed, and the reduced globule will remain, either in naptha, or otherwise separated from all contact with oxygen. See BITITM EN.
One part of the base of alkali and two of mercury, estimated by bulk, form an amalgam, which when applied in the cir cle of a galvanic battery, producing an intense heat to iron, silver, gold, or pla tina, immediately dissolved them, and converted them into oxides, in which pro cess alkali was regenerated. Glass, as well as all other metallic bodies, was also dissolved by the application of this sub stance : the base of the alkali seizing the oxygen of the manganese and of the mi. nium, potash was regenerated. One of these globules placed on a piece of ice dissolved it, and burnt with a bright flame, giving out an intense heat. Potash was found in the product of the dissolved ice. Nearly the same effects followed, when a globule was thrown into water : in both cases a great quantity of hydro. gen was rapidly liberated. When laid on a piece of moistened turmeric paper, the globule seemed instantly to acquire an in tense heat; but so rapid was its move ment in quest of the moisture, that no part of the paper was burnt, only an in tense deep red stain marked the course it followed, and showed a reproduction of alkali. The specific gravity of the base of soda is as seven to ten off' water : it is fixed in a temperature of about 150°, and fluid at 180°. Mr Davy next tried its effects on the phosphates, phosphurets, and many other salts of the first and se cond degree of oxydizement, all of which it decomposed, seizing their oxygen, and reassuming its alkaline qualities. From many experiments it appears, that 100 parts of potash contain 15 of oxygen, and 85 of an inflammable base, and that the same quantity of soda contains 20 of au gen, and 80 base This ingenious chemist, after a great number of complex experi ments, in which he was assistoc1 by Mesa's. Pepys and Allen, ascertained that oxygen is also an essential ingredient in ammo nia; of which 100 grains appeared to yield 20 of oxygen. Mr. Davy has also found that oxygen is one of the constituent prin ciples of the earths barytes and stron tites. See Cinoi STAY, POTASH, and