"The experiments which Mr. Dalton has made on the analysis of ether, show in a very satisfactory manner, that the notion which I threw out in my System of Chemistry, that sulphuric ether is a compound of two atoms olefiant gas, and one atom vapour of water condensed into one volume, is the true one." " Hence 2 volumes olefiant gas weigh 1.9416 Specific gravity of ether vapour 2.5860."-Annals of Philosophy, August 1820, p. 81. Historical Sketch, &c. by Thomas Thomson, M. D. &c. Now, though in that Sketch the Dr. seems to show, that Mr. Dalton was unacquainted with M. Gay-Lussac's researches on ether, it was a rather rash presumption to extend that analogy of ignorance to all other British Chemists. The first of the Doctor's periods, quoted above, is nonsense, from his use of the favourite word atom, instead of volume. The statement in the second is taken from M. Gay-Lussac, and bears the elegant impression of its author. Glasgow, Nov. 7, 1820. N. B. The Articles with the asterisk (*), are inserted by Dr. Ure; the others, with the exceptions noticed in the Introduction, are reprinted from NICHOLSON's Octavo Dictionary. PREFATORY REMARKS, BY DR. HARE. Being requested by the publisher to make any additions or corrections in this American edition of Ure's Nicholson's Dictionary, which might to me appear proper, I have complied as far the allotted time would permit. This, however, was so short, that I have only been enabled to write on some of the topics, concerning which my practical experience, and peculiar and mature reflections, have qualified me to comment advantageously. The passages added by me will be distinguished by a cross (†), as those by Dr. Ure are by an asterisk. After the above was written, pursuant to my advice, the publisher engaged Dr. Franklin Bache to revise the work, and read the proofs. I feel it due to Dr. Bache to state, that I am under the impression that he has performed his office with zeal and ability; and that I conceive the work will be much indebted to him for its typographical correctness. His scientific knowledge has enabled him, not only to prevent various new errors, but to correct many previously existing in the original English copy. DICTIONARY OF CHEMISTRY. ABS BSORBENT. An epithet introduc ed into chemistry by the physicians, to designate such earthy substances, as seemed to check diarrhea, by the mere absorption of the redundant liquids. In this sense it is obsolete and unfounded. Professor Leslie has shown that the faculty of withdrawing moisture from the air, is not confined to substances which unite with water in every proportion, as the strong acids, dry alkalis, alkaline earths, and deliquescent salts; but is possessed by insoluble and apparently inert bodies, in various degrees of force. Hence the term Absorbent merits a place in chemical nomenclature. The substance whose absorbent power is to be examined, after thorough desiccation before a fire, is to be immediately transferred into a phial, furnished with a well ground stopper. When it is cooled, a portion of it is transferred into a large wide-mouthed bottle, where it is to be closely confined for some time. A delicate hygrometer being then introduced, indicates on its scale the dryness produced in the inclosed air, which should have been previously brought to the point of extreme humidity, by suspending a moistened rag within the bottle. The following table exhibits the results of his experi ments: The more a soil is comminuted by labour and vegetation, the greater is its absorbent power. This ingenious philosopher infers, that the fertility of soils depends chiefly on their disposition to imbibe moisture; and illustrates this idea by recent and by disintegrated lava. May not the finely divided state most penetrable by the delicate fibres of plants, derive its superior power of acting on atmospherical vapour from the augmentation of its surface, or the multiplication of the points of contact? In similar circumstances 100 gr. of the following organic substances absorb the following quantities of moisture: Ivory 7 gr. boxwood 14, down 16, wool 18, beech 28. -Leslie on Heat and Moisture.* ABSORPTION. By this term chemists understand the conversion of a gaseous fluid into a liquid or solid, on being united with some other substance. It differs from condensation in this being the effect of mechanical pressure, or the abstraction of caloric. Thus, if muriatic acid gas be introduced Carbonate of magnesia 75 Carbonate of lime 70 Silica 40 Carbonate of barytes Carbonate of strontites 32 .. 23 .. Alumina causes a dryness of 84 degrees. into water, it is absorbed, and muriatic acid is formed; if carbonic acid gas and ammoniacal gas be brought into contact, absorption takes place, and solid carbonate of ammonia is produced by the union of their ponderable bases. Pipe clay 85 Greenstone, or trap in powder 80 There is a case of condensation, which has sometimes no doubt been mistaken for A absorption, though none has taken place. When an inverted jar containing a gas confined by quicksilver is removed into a trough of water, the quicksilver runs out, and is replaced by water. But as the specific gravity of water is so much inferior to that of quicksilver, the column of water in the jar resists the atmospheric pressure only with one 14th of the power of the quicksilver, so that the gas occupies less room from being condensed by the increased pressure, not from absorption. ABSTRACTION. In the process of distillation, the volatile products which come over, and are condensed in the receivers, are sometimes said to be abstracted from the more fixed part which remains behind. apart This term is chiefly used when an acid or other fluid is repeatedly poured upon any substance in a retort, and distilled off, with a view to change the state or composition of either. See DISTILLATION. * ACANTICONE. See PISTACITE.* * ACERATES. The acer compestre, or common maple, yields a milky sweetish sap, containing a salt with basis of lime, possessed, according to Scherer, of peculiar properties. It is white, semi-transparent, not altered by the air, and soluble in nearly 100 parts of cold, or 50 of boiling water.* * ACERIC ACID. See ACID (ACERIC).* * ACESCENT. Said of substances which become sour spontaneously, as vegetable and animal juices, or infusions. The suddenness with which this change is effected during a thunder storm, even in corked bottles, has not been accounted for. In morbid states of the stomach, also, it proceeds with astonishing rapidity. It is counteracted by bitters, antacids, and purgatives.* ACETATES. The salts formed by the combination of the acetic acid with alkalis, earths, and metallic oxides. See the different bases. * ACETIC ACID. See ACID (ACETIC).* * ACETOMETER. An instrument for estimating the strength of vinegars. It is described under ACID (ACETIC).* ACETOUS. Of or belonging to vinegar. See ACID (ACETIC.) ACHROMATIC. Telescopes formed of a combination of lenses, which in a great measure correct the optical aberration, arising from the various colours of light, are called achromatic telescopes. Some of these have been made wonderfully perfect, and their excellence appears to be limited only by the imperfections of the art of glass-making. The artifice of this capital invention of Dollond consists in selecting, by trial, two such pieces of glass, to form the object lenses, as separate the variously coloured rays of light to equal angles of divergence, at different angles of refraction of the mean ray; in which case it is evident, that, if they be made to refract towards contrary parts, the whole ray may be caused to deviate from its course without being separated into colours. The difficulty of the glass-maker is in a great measure confined to the problem of making that kind of glass which shall cause a great divergence of the coloured rays with respect to each other, while the mean refraction is small. See GLASS; also APLANATIC. * ACIDS. The most important class of chemical compounds. In the generalization of facts presented by Lavoisier and the associated French chemists, it was the leading doctrine that acids resulted from the union of a peculiar combustible base called the radical, with a common principle technically called oxygen, or the acidifier. This general position was founded chiefly on the phenomena exhibited in the formation and decomposition of sulphuric, carbonic, phosphoric, and nitric acids; and was extended by a plausible analogyto other acids whose radicals were unknown. "I have already shown," says Lavoisier, " that phosphorus is changed by combustion into an extremely light, white, flaky matter. Its properties are likewise entirely altered by this transformation; from being insoluble in water, it becomes not only soluble, but so greedy of moisture as to attract the humidity of the air with astonishing rapidity. By this means, it is converted into a liquid, considerably more dense, and of more specific gravity than water. In the state of phosphorus before combustion, it had scarcely any sensible taste; by its union with oxygen, it acquires an extremely sharp and sour taste; in a word, from one of the class of combustible bodies, it is changed into an incombustible substance, and becomes one of those bodies called acids. "This property of a combustible substance, to be converted into an acid by the addition of oxygen, we shall presently find belongs to a great number of bodies. Wherefore strict logic requires that we should adopt a common term for indicating all these operations which produce analogous results. This is the true way to simplify the study of science, as it would be quite impossible to bear all its specific details in the memory if they were not classically arranged. For this reason we shall distinguish the conversion of phosphorus into an acid by its union with oxygen, and in general every combination of oxygen with a combustible substance, by the term oxygenation; from this I shall adopt the verb to oxygenate; and of consequence shall say, that in oxygenating phosphorus, we convert it into an acid Sulphur also, in burning, absorbs oxygen gas; the resulting acid is considerably heavier than the sulphur burnt; its weight is equal to the sum of the weights of the sulphur which has been burnt, and of the oxygen absorbed; and, lastly, this acid is weighty, incombustible and miscible with water in all proportions." tains oxygen, although this may be an inducement to suspect its existence in it; still less should we conclude, because a substance contains oxygen, that it must have acid properties; on the contrary, the acidity of an oxygenated substance shows that the oxygen has only experienced an incomplete saturation in it, since its properties rem: in predominant." Amid the just views which pervade the early part of this quotation from Berthollet, it is curious to remark the solecism with which it terminates. For after maintaining that acidity may exist independent of oxygen, and that the presence of oxygen does not necessarily constitute acidity, he concludes by considering acidity as the criterion of unsaturated oxygen. This unwarrantable generalization of the French chemists concerning oxygen, which had succeeded Stahl's equally unwarrantable generalization of a common principle of combustibility in all combustible bodies, was first experimentally combated by Sir H. Davy, in a series of admirable dissertations published in the Philosophical Transactions. "I might multiply these experiments, and show, by a numerous succession of facts, that all acids are formed by the combustion of certain substances; but I am prevented from doing so in this place by the plan which I have laid down, of proceeding only from facts already ascertained to such as are unknown, and of drawing my examples only from circumstances already explained. In the mean time, how ever, the examples above cited may suffice for giving a clear and accurate conception of the manner in which acids are formed. By these it may be clearly seen that oxygen is an element common to them all, and which constitutes or produces their acidity; and that they differ from each other according to the several natures of the oxygenated or acidified substances. We must, therefore, in every acid carefully distinguish between the acidifiable base, which M. de Morveau calls the radical, and "the acidifying principle or oxygen." Elements, p. 115. Although we have not yet been able either to compose or to decompound this acid of sea salt, we cannot have the smallest doubt that it, like all other acids, is composed by the union of oxygen with an acidifiable base. We have, therefore, called this unknown sub-ped in the above substances by the addi. stance the muriatic base, or muriatic radical." P. 122. 5th Edition. Berthollet's sound discrimination led him to maintain that Lavoisier had given too much latitude to the idea of oxygen being the universal acidifying principle. "In fact," says he, " it is carrying the limits of analogy too far to infer, that all acidity, even that of the muriatic, fluoric, and boracic acids, arises from oxygen, because it gives acidity to a great great number of substances. Sulphuretted hydrogen, which really possesses the properties of an acid, proves directly that acidity is not in all cases owing to oxygen. There is no better foundation for concluding that hydrogen is the principle of alkalinity not only in the alkalis, properly so called, but also in magnesia. lime, strontian, and barytes, because ammonia appears to owe its alkalinity to hydrogen. "These considerations prove that oxygen may be regarded as the most usual principle of acidity, but that this species of affinity for the alkalis may belong to substances which do not contain oxygen; that we must not, therefore, always infer, from the acidity of a substance, that it con His first train of experiments were instituted with the view of operating by voltaie electricity on muriatic and other acids freed from water. Substances which are now known by the names of chlorides of phosphorus and tin, but which he then supposed to contain dry muriatic acid, led him to imagine intimately combined water to be the real acidifying principle, since acid properties were immediately develo tion of that fluid, though previously they exhibited no acid powers. In July 1810, however, he advanced those celebrated views concerning acidification, which, in the opinion of the best judges, display an unrivalled power of scientific research.The conclusions to which these led him, were incompatible with the general hypothesis of Lavoisier. He demonstrated that oxymuriatic acid is, as far as our knowledge extends, a simple substance, which may be classed in the same order of natural bodies as oxygen gas, being determined like oxygen to the positive surface in voltaic combinations, and like oxygen combining with inflammable substances, producing heat and light. The combinations of oxymuriatic acid with inflammable bodies were shown to be analogous to ox ides and acids in their properties and pow ers of combination, but to differ from them in being for the most part decomposable by water: And finally, that oxymuriatic acid has a stronger attraction for most inflammable bodies than oxygen. His preceding decomposition of the alkalis and earths having evinced the absurdity of that nomenclature, which gives to the general |