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but nevertheless they appear to belong to a certain limited number of forms, which repeatedly occur and may in variably be referred to the same general order or system. This system is, or appears to be, what may be termed an homologous series of " oxycarbons," of which the uiiit of carbon with the weight 12 may be regarded as the first term, and of which the adjacent terms differ by an incre ment of carbonic oxide, CO, weighing 28, precisely as homologous series of hydrocarbons differ by the increment CH 2 . Two at least of these substances have been identified

by analysis, namely, the adjacent terms C 4 O 3 and C 5 O 4 .

Carbonic Acid.—Carbonic dioxide dissolves in about its own volume of water at ordinary temperatures, forming carbonic acid, H 2 C0 3 ; the solution has a sharp and slightly acid taste, and turns the blue colour of litmus to wine-red. The volume of carbonic dioxide dissolved by water diminishes as the temperature rises, and at the boil ing heat the whole is expelled from solution ; the volume dissolved by water at a given temperature is nearly the same, however, under all pressures, so that the weight of gas absorbed increases in nearly the same proportion as the pressure. On removing the pressure the gas is given off with effervescence. Ordinary soda-water consists merely of water impregnated with carbonic dioxide by mechanical pressure. When lime water is added to a solution of carbonic acid, or carbonic dioxide is passed into lime water, a white precipitate of calcic carbonate or carbonate of lime, the chief constituent of ordinary chalk, is produced:—

CaO g H 2 + H 2 C0 3 = CaC0 3 + 2H 2 O . Calcic hydrate. Carbonic acid. Calcic carbonate. Water.

On continuing to pass the gas the precipitate becomes dissolved owing to the formation of an acid carbonate or bicarbonate, which is fairly soluble in water, the carbonate being almost insoluble:—

CaC0 3 + H 2 C0 3 = H 2 Ca(C0 3 ) 2 Calcic carbonate. Carbonic acid. Calcic bicarbonate.

If the solution of the bicarbonate be heated, carbonic dioxide is given off and the calcic carbonate is precipitated, the bicarbonate being decomposed. The lime salt may also be removed from the solution, with the exception of the small amount of calcic carbonate which the water is capable of dissolving, by carefully adding lime water or a solution of ordinary washing soda as long as a precipitate is produced. The action of lime water in this case is to convert the soluble bicarbonate into the insoluble carbonate ; thus:—

H 2 Ca(C0 3 ) 2 + CaH 2 2 = 2CaC0 3 + 2H 2 0. Calcic bicarbonate. Cattle hydrate. Calcic carbonate.

These facts serve to explain the "hardness," as it is termed, of many natural waters, and the methods employed to render such waters soft. A water which, like rain water, readily produces a lather with soap is said to be a soft water, whereas one which does not readily yield a lather, but forms a large amount of curd, is said to be a hard water. The hardness of most natural spring waters is chiefly due to dissolved calcic bicarbonate, which is formed by the action of the carbonic acid dissolved in rain upon the calcareous materials with which the water comes in contact during its passage through the earth. Ordinary soap consists of the sodic salts of certain fatty acids, and is soluble in water ; but the lime salts of these acids are insoluble, so that when the soap is used with the hard water a double decomposition takes place, the calcic bicar bonate being converted into sodic bicarbonate and the soda- soap into a lime soap or curd. Such waters may be rendered soft, that is to say, the calcic bicarbonate may be removed in a variety of ways, viz., by heating the water, which causes the decomposition of the bicarbonate and the precipi tation of the carbonate, and it is in this way that the fur is produced in our kettles and boilers ; by adding washing soda or sodic carbonate, a common practice in all households where hard water is used ; and lastly, by adding lime water.

(h. e. a.)

CARBONARI, The (from the Italian carbonaro, charcoal-

maker), were certain secret societies of a liberal and even, revolutionary tendency that took an active part in some events of Italian and French history during the first three decades of this century. Secret societies, calling themselves by this or a similar name, had indeed previously existed in various parts of Europe ; but it was in Italy, towards the close of the Napoleonic wars, that these first began to assume an historic importance. In 1808 many republi cans, discontented alike with the Bourbon and the Boua- partist government in Naples, had retired to the mountain recesses of the Abruzzi and Calabria. At first engaged only in an isolated resistance to the authorities, they began to organize themselves. They took the name of Carbonari, a name suggested by the trade of charcoal-burning extensively pursued in those regions, in which many of them were engaged. From this trade, too, but especially from the Christian religion, and above all from the crucifixion of Christ, they adopted a system of mystic rites and a symbolic phraseology, by which they concealed from the uninitiated, but all the more vividly expressed to the initiated, the real political aims of the society, while its apparently religious character served to attract many whom its revolutionary secrecy might have repelled. A lodge of Carbonari was baracca (a hut) ; an ordinary meeting, vendita (a sale) ; a meeting of importance, alia vendita ; these terms being borrowed from the trade of charcoal-burning. But for words to express the inner purpose of the society they borrowed from religion. Christ, as the highest victim of tyranny, was the lamb that had been put to death by the wolf ; they were sworn to avenge his death ; and so the destruction of the wolf to avenge the slaughter of the lamb became the symbolic watchword of the society. There were four grades in the society ; and the ceremonies of initiation were characterized by many mystic rites, through which the real meaning began only gradually to appear. Many efforts were made to bring about a complete organ ization of the Carbonari in Italy, by the institution of a central power which should control the separate societies of the various provinces, but they failed. Politicians soon discovered how easily capital could be made of such societies, and negotiations were entered into by the Bourbons to unite the Carbonari in an effort to overthrow the French Government in Naples. Accordingly, for two years they carried on a desultory warfare with King Murat, who at last, taking the matter thoroughly in hand, drove them into the mountains, from which they had emerged, and sup pressed them for a time. Capobianco, their leader, was treacherously arrested and put to death. Ere long, the Carbonari reappeared and helped towards the final over throw of the French power in Naples. But Ferdinand, who had courted them during his misfortunes, proved false to them on his return to power, though they were moderate enough in their political aims, being ready to content themselves with the establishment in Naples of the constitution that had been enjoyed in Sicily under English supremacy. Henceforward they began to conspire against the Bourbon Government, and indeed soon spread over the whole of Italy, being more and more regarded as the champions of the liberal and national cause. They were the principal authors of the Neapolitan revolution of 1820, of the disturbances in the Papal States of the same year, and of the Piedmontese revolution of 1821. Previously recruited chiefly from the lower classes, the Carbonari now counted in their ranks

almost all the intelligent and patriotic population of Italy,