ELEMENTS OF CHEMISTRY.
[This is one of the Naturo-Philosophical volumes of the Cabinet Cyclopaedia, and is therefore to be viewed as a portion of that series rather than as a substantive work. Its preparation has been entrusted to Mr. M. Donovan, Professor of Chemistry to the Company of Apothecaries in Ireland; so that it comes to us with some share of recommendatory experience on the part of the editor. It would, however, be difficult to point out the advantages of Mr. Donovan's volume over others of the same description. Neither will such distinction be looked for but in a scientific journal. The arrangement is clear and satisfactory; the manner plain and illustrative; and the matter in accordance with the science of the present day; though in a few cases the nomenclature is somewhat overloaded with hard names, and presumes more previous acquaintance with the subject than is consistent. We subjoin a few extracts of popular interest.]
Caloric, or the matter of Heat.
Heat is admitted by the philosophers of the present day to be the principle concerned in repulsion; and heat and cold are known to produce expansion and contraction in all bodies. Heat is, therefore, the antagonist of cohesion. Chemists have thought it necessary to make a distinction between the senses in which the word heat may be taken. In its usual acceptation, it merely means the effect excited on the organs of sensation by a hot body. But as this must be produced by a power in the hot body independent of sensation, that power is what chemists understand by the word heat: and to distinguish between the effect and its cause, the term caloric has been substituted. The introduction of this term appears altogether unnecessary, when the sense in which the word heat should be understood is explained. Caloric means the cause of the sensation heat: and there seems no reason to fear that the perception of heat by the organs of sensation can ever be misunderstood to be the agent in chemical phenomena.
Omniscience displayed in the constitution of the Atmosphere.
In the constitution of the atmosphere we have ample scope to admire the design and execution of a structure calculated, with such wondrous precision, to fulfil its purposes. Were the atmosphere to consist wholly of oxygen; and the different kinds of objects which compose, and are found upon, the globe, to remain what they are; the world would run through its stages of decay, renovation, and final destruction, in a rapid cycle. Combustion, once excited, would proceed with ungovernable violence; the globe, during its short existence, would be in a continual conflagration, until its ashes would be its only remains: animals would live with hundred-fold intensity, and terminate their mortal career in a few hours. On the other hand, were the atmosphere wholly composed of azote, life could never have existed, whether animal or vegetable, and the objects of the Creator in forming this world would not be fulfilled. But the atmosphere is a wholesome mixture of these two formidable elements, each neutralizing the other's baneful influence. The life of animals quietly runs through its allotted space; and the current of nature flows within prescribed limits, manageably and moderately.
Tartaric Acid.
Every one knows, that when a large quantity of the juice of grapes is left to spontaneous fermentation, the result is wine. When wine has been kept some time to depurate in wooden vessels, it deposits, on the side of the vessel, a hard crust of dark coloured matter, the taste of which is sour. This matter is impure; but, when purified by various crystallizations, it becomes perfectly white and crystalline; and then it is known in commerce by the name of cream of tartar. The etymology of the singular name, tartar, is uncertain: it is derived from tártaros, as some say, because it occasions pains equal to those endured in the infernal regions; and, as others say, merely because this substance deposits itself in the inferior parts of the cask. Tartaric acid may be obtained from cream of tartar by a process analogous to that given for obtaining citric acid. It has an exceedingly acid taste: it dissolves readily in water, and is soluble in alcohol. Its crystals are of a very irregular shape. In 100 parts, by weight, there are 12 of water; the remaining 88 parts are the pure anhydrous acid, composed of 32-39 parts of carbon, 52-97 of oxygen, and 2-64 of hydrogen. This acid exists abundantly in other fruits, but especially in the tamarind; in the grape it exists along with citric, malic, and an acid called vinic, which resembles tartaric acid in many respects, but differs from it in others, and concerning the nature of which almost nothing is known: these four constitute the agreeable tartness of the juice of that fruit.
Oxalic Acid.
The plant called sorrel is valued for its acidulous taste. This acidity is owing to the presence of a peculiar acid, which may be separated from the juice, and from the potash with which it is combined, by a process analagous to that described for the preparation of citric acid. It has obtained the name of oxalic acid, from the generic name of the plant, oxalis acetosella. This acid forms readily into regular crystals, of which one half the weight is water, the other half being pure acid. It is a remarkable circumstance in its constitution, that it contains no hydrogen, and that it consists merely of carbon and oxygen—there being twice as much oxygen as there is carbon. So that it differs from carbonic acid merely in the relative quantities of its ingredients. Oxalic acid can be prepared by an artificial process, with great ease, from sugar, and six times its weight of nitric acid,—the former affording the carbon necessary to its formation, and the latter the oxygen. It is only necessary to heat the nitric acid on the sugar; the sugar dissolves, and there is a violent effervescence, which must be moderated by immersion in cold water: when the mixture cools, crystals of oxalic acid form in abundance, which may be purified by a second crystallization.
Oxalic acid is an active poison; many persons have fallen victims to its virulence, by having swallowed it in mistake for Epsom salt, which it resembles in appearance. In all probability, this would not prove to be the only vegetable acid capable of acting as a poison. Chalk finely powdered, and diffused in water, is the proper antidote to the poison of oxalic acid.
[The chapter on Combustion contains some new facts; and that on the Atomic Theory is more attractive than might have been expected.]