The pure salt may be prepared artificially for use as a pigment, by adding dilute sulphuric acid to a solution of chloride of baryta, when a white precipitate is formed ; this is well washed and dried. It is a heavy, white powder, insoluble in water and nearly insoluble in all other menstrua. It may also he prepared by heating the native mineral, grinding it to powder, and well washing it, first in dilute sulphuric acid, in order to remove any traces of iron, and afterwards in water; the white powder is afterwards thoroughly dried. This process is employed at several works in the neighbour hood of Matlock Bath, in Derbyshire, but much larger quantities could be produced in different parts of the country, if the demand for the article rendered its production more profitable. The principal use of sulphate of baryta is to adulterate white lead, and to form the pigment known as blanc fire, or permanent white. For these purposes, the native mineral, ground and washed, as described above, is commonly employed. It is also used in paper-making, and as a substitute for the more expensive nitrate in some of the processes of pyrotechny. Sulphide of barium is pre pared from the sulphate by heating it to redness in a covered crucible with charcoal.
BEVERAGES.—By the term "beverages " are here understood those common drinks which are not the products of distillation. Those which have been produced by that process have already been treated of as Alcoholic Liquors. Many of these beverages, however, as beer and wine, contain alcohol as a product of their fermentation.
Aerated Water. (Fe., Eau gaseuse ; GER., Gashaltige Wasser.)—This name is given to a variety of natural and artificial drinks, consisting of water impregnated with carbonic acid gas. The consumption of these drinks is, at the present time, very great, and it is, moreover, rapidly increasing. Thirty years ago, two hundred thousand bottles were consumed annually in France; now, two hundred million bottles are scarcely sufficient to satisfy the demand in that country. In America, aerated waters have come still more rapidly into favour. In our colonies, these refreshing beverages are largely drunk, and in these countries, as well as in our own land, the consumption is daily increasing. Hence, their manufacture has become a staple industry of rising importance.
The sparkling and refreshing qualities of aerated beverages, and in some measure their taste and hygienic properties, are due to the presence of carbonic acid gas (see Carbonic Acid). All natural mineral waters contain it in greater or less quantity, owing to the action of certain subterranean forces. In wine and ale it is formed during fermentation. And it is introduced into artificially aerated drinks by the help of various chemical and mechanical operations, to be described hereafter. In all these beverages, the role played by the gas is threefold : to give them a sparkling effervescence, thereby rendering them far more refreshing than they were before aeration ; to afford them an agreeable, piquant flavour; and, as in the case of natural waters especially, to render them capable of holding in solution certain mineral salts which possess valuable medicinal properties.
The physiological effects of this gas upon the human organism are well known. It exerts a peculiar action upon the nervous system, and especially upon the brain ; but these effects are dangerous only when long continued, or when the gas is respired in large quantities, and unmixed with air. Generally, it has a pleasant, exhilarating influence, a notable instance of which is seen in the effect of champagne, a wine containing a large proportion of carbonic acid gas. This gas has also a favourable action upon the organs of digestion. Its presence in wines and ales renders them digestive, as well as agreeably pungent ; when the gas has been allowed to escape, they lose the former property, becoming at the same time unpleasantly insipid and flat-tasted. For this reason, all beverages which contain carbonic acid gas are more wholesome when drunk immediately after the bottles are opened.
At ordinary temperatures, water dissolves naturally its own volume of carbonic acid, and alcohol nearly three times as much. By pressure, and with the help of agitation, it may be made to take up a quantity directly proportional to the pressure exerted ; that is, by doubling the pressure, we double the quantity of gas absorbed by the water. Hence, the weight of the atmosphere being 15 lb. to the square inch, by applying a pressure of 15 lb. to the inch, we force the water to take up twice the quantity of gas it is capable of absorbing when not subjected to pressure ; when, however, the pressure is removed, the gas which has been absorbed in consequence of its application escapes rapidly, causing the phenomenon known as effervescence.
In beer and wine, as remarked above, the presence of carbonic acid gas is due to fermentation. During this process, the sugar contained in the wort or lees from which the beer or wine is made, is decomposed, alcohol and carbonic acid gas being formed. A portion of the latter remains in the liquor after fermentation, and thus imparts to it the sparkling and refreshing qualities which are so highly valued in these beverages.
The presence of an elastic, gaseous body in the water yielded by many springs was well known to the ancients, and was mentioned in the writings of Pliny, Galen, Celsus, and others. In later times, Van Helmont, Boyle, and Bergmann discovered that the gaseous substance was of the same nature as that produced by the combustion of carbon and the decomposition of marble. The investi gations of science have since shown that this gas is a compound of carbon and oxygen, and to it waa given the name of carbon dioxide, or carbonic acid. In these mineral waters, it is contained either in tho free state, or as carbonates, in combination with lime, soda, magnesia, ammonia, potash, iron, manganese, cobalt, nickel, strontium, copper, lithiutn, &c. In most of these springs, the gas holds in solution certain salts which are precipitated when it is removed by evaporation. The beverages width are made in imitation of these natural waters are, as already stated, imprc.gnated artificially with the gas. For this purpose, it is usually obtained by the action of an acid upon refttse marble, whiting, and other forms of carbonate of Erne. •