By means of the spectrum analysis, litbia has been shown to exist in minute quantities in sea water and in many mineral waters ; in blood, milk, and the ashes of some plants ; and that instead of being a very rare substance, as had always been supposed, it exists in a state of very wide diffusion. The plincipal source of lithia is a bot spring, lately discovered in the Huel Seton mine, Cornwall, which contains about 31 grains of chloride of lithia per gallon. The only application of lithia at present is as a medicine, in which the whole supply is consumed.
confusion has, al ways entered into the use of the terms kali, alkali, potash aud soda, arising probably from the very familiarity with which from ancient times the substances have been regarded. The term " alkali," as is well-known, was applied by tho Arabians to the various soda salts obtained from the ashes of marine plants. Afterwards the salts of potash, similarly found in the ashes of land plants, and the carbonate of ammonia were included in the term, the word "potash " signifying evidently a preparation of the ashes of plants in pots. Probably both potash and soda were known to the ancients, and some vague distinction between them recognized, as for instance, when in Jeremiah ii. 22, "nitre and much sope" are men tioned as possessing evidently different cleansing properties. Pliny speaks of a soap made from the ashes of plants and grease, and it is very likely, from the evidence of several of the old writers, that the causticizing effect of lime upon solutions of alkali was known. It may be noticed that the particular character of this reaction—the withdrawal of carbonic acid—was first explained by Black.
An exact line of demarcation between potash and soda was first drawu by Duhamel in 1736. Up to that time ammonia and various of its salts had been distinguished as " volatile " alkalies, and the potash and soda salts, indiscriminately, as "fixed" alkalies. Potash was forthwith styled. " vegetable " alkali, because it was supposed to be produced solely from the ashes of plants, and soda, "mineral" alkali, from its existence in rock salt, &c. Klaproth proved that the salts of potas sium aLso existed in various forms in minerals, and substituted the term " kali" for vegetable The term " potash," too, is often employed in a very loose manner, to designate sometimes the hydrate of potassium, sometimes the carbonate, sometimes the oxide, and so on. As far as possible in the present work, the term will ls. confined to the hydrate—KHO.
The metal potassium, in combination, besides yielding four oxides—monoxide, K,O ; dioxide, ; trioxide, ; tetroxide, present, chiefly interesting to the student of chemi-try, forms a series of salts of very great importance in the arts and manufactures. These will now be considered in order.
111,1,1tte of Potassium. (Fa., Hydrate de potasse, or, simply, Potasse ; Gen., Bali ).—Synonyms,
potash ; potash hydrate ; potassium hydroxide ; caustic potash. Formula, KHO. Combining weight, 48.1 ; specific gravity, This substance, usually termed caustic potash, was formerly supposed to be simply an oxide of potassium. Darcet, howover, showed in 1808 (ann. Chim. lxviii., 175), that some other body was present besides oxygen and potassium—or soda, and it was then commonly believed that the oxido was combined with water. It was not until comparatively recent times that caustic potash was in reality a hydroxide, a compound derived from water by substituting potassium for a portion of the hydrogen.
The hydrate of potassium, or caustic potash, is a hard, white solid, with occasionally a fibrous structure, soluble in about half its weight of water (1 part dissolving parts of KHO), freely soluble in naphtha, glycerine, and alcohol, and to some slight extent in ether. For water it has a very strung affinity, absorbing it greedily from the air upon exposure, and passing, first into a carbonate, and finally into a bicarbonate, through combination with carbon dioxide. Its combina tion with water is accompanied by a considerable evolution of heat. When the concentrated solution is cooled the hydrate KHO + 21-1,0 crystallizes out in clear colourless acute rhombohodra. Two distinct hydrates are formed with water, the one having a formula K110 + and tho other KEIO + 2 The following tables drawn up by Dalton and Tunnermann give somewhat varying percentages of hydrate and monoxide contained in aqueous solutions at 15' temperature, and different densities :— In either a liquid or solid state, caustic potash is a most powerful alkali, neutralizing acids, decomposing metallio salts, possessing a vigorous corrosive action upon animal and vegetable tissues, turning reddened litmus solution blue, turmeric brown, and producing a purple colour with an infinitely dilute solution of alizarin, or an acidified solution in alcohol of cochineal, or logwood. It destroys many of tho silicates—and hence, should not be kept in glass or porcelain vessels— forming silicate of potassium, and separating the bases. Especially is it destructive to a lead-glass, dissolving out the lead oxide. Its action upon most organic bodies is to take from them the carbon and oxygen necessary for its conversion into carbonate. At a temperature somewhat below redness caustic potash melts to a thick colourless liquid, possessing the most powerful caustic properties. At a full red heat it volatilizes in white feathery fumes, being decomposed into potassium, hydrogen and oxygen. It forms soaps with various fats, oils aud resins, and dissolves sulphur, the sulphides of antimony, arsenic, &c., also many bases—alumina, silica, &c.