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ART. V. The Painter and Varnisher's Guide; or a Treatise, both in Theory and Practice, on the Art of making and applying Varnishes on the different Kinds of Painting; and on' the Method of preparing Colours, both simple and compound. By P. F. TINGRY, Professor of Chemistry, Natural History, and Mineralogy, in the Academy of Geneva, 8vo. pp. 600.

THE present volume was composed at the request of the society established at Geneva for the encouragement of the arts, agriculture, and commerce, in consequence of instructions from the society to its committee of chemistry, to undertake the elucidation of those arts of which no account had been published by the academy of sciences at Paris. In the general distribution of subjects, the art of varnishing was entrusted to M. Tingry, and the present work is an evidence that he has ably fulfilled the trust committed to him.

The general principles of varnishmaking were understood before M. Tingry's work made its appearance, and an infinite number of receipts, good, bad, and indifferent, were scattered through various publications. It was however greatly to be desired, that all the floating knowledge on this subject, purified from the numerous absurdities and errors by which it was obscured, should be col lected in a systematic and orderly arrangement. This task M. Tingry has undertaken, and, upon the whole, has performed it well: he has also added several new facts of considerable importance, so that we do not hesitate to recommend the work before us as greatly superior to all others on the same subject, with which we are acquainted. The great fault, and which peculiarly characterizes the recital of M. Tingry's own experiments, is prolixity; but this is the national feature of Genevan literature.

This treatise is divided into two parts, each of which is again subdivided into chapters.

The first chapter is an enumeration and short history of the substances which form the basis of varnishes, together with the criterions by which the best and purest of each kind may be ascertained.

The second chapter relates to the fluid vehicles of varnishes, or solvents. These are alcohol, the essential oils of turpentine, lavender, and spike, and the expressed oils of poppy-seed, nuts, and linseed. In treating of the last of these substances, the author enters into a long

and interesting account of the various methods by which oils are made drying, and the effect of garlic on oils. The third chapter is introduced by some general observations on the art of the varnisher, and then proceeds to give a de-, tailed description of varnishes, arrang ed in five genera. The first includes the drying varnishes, prepared with alcohol; the second describes those alcoholic varnishes which are not so drying as the former: under which is included the transparent gold coloured varnish, so extensively employed by workers in metal to communicate to brass, iron, tin, &c. the colour and lustre of gilding. The third genus is composed of those species in which oil of turpentine is the solvent. The fourth genus is formed of the colourless, or nearly colourless, copal varnishes: the experience of M. Tingry on the solvent power of oil of turpentine on unprepared copal, by no means agrees with Mr. Sheldrake's excellent experiments on the same subject; but the reason of this difference evidently is the inferiority of the oil of turpentine made use of by M. Tingry, when compared with that employed by Mr. Sheldrake. M. Tingry finds that the fusion of copal by the lowest possible degree of heat, renders it much more soluble than before, and that long exposure to the action of the light considerably increases the specific gravity of oil of turpentine, and renders it a much more efficacious solvent of copal. The fifth genus of varnishes comprehends those whose base is fat oil, including the amber varnishes, the varnish for carriages, and the lacquer for waiters, tea-pots, and all other artis cles of japanned ware.

The fourth chapter treats of the preparation of varnish on a large scale, and contains many useful precautions and modes of manipulation.

The fifth chapter contains observations on the effect of solar light on oil of turpentine, particularly with regard to the solvent power on copal, thus communicated to it. This chapter, although very unsatisfactory and most tediously prolix, contains some interesting facts which merit further enquiry,

The second part of this work, by attempting to comprehend too much, is by no means equal to the former part; yet many useful facts are dispersed through it, and the artist will find here, collected into one mass, a considerable quantity of miscellaneous information from various quarters.

The first chapter relates to colouring matters, and the methods of preparing them for use. The second chapter is entitled "a philosophical account of the origin of colours, with a description of the processes which art employs to vary the number and richness of the tints, resulting from a mixture of them." The philosophical part of the chapter is dispatched in the three first pages, the remainder is a practical account of the kinds and proportions of colouring substances, required for the various tints that are used by the painter. The third chapter is one of the most valuable it describes the methods of colouring the hard copal varnish, and the successful

application of it in imitation of vi treous enamel. The fourth chapter contains useful precepts on the applica tion of varnish to various substances, on the method of preserving brushes after they have been used, of taking paint stains out of cloaths, and sundry other interesting matters. The fifth chapter treats of painting in distemper; and the volume is concluded by a short chapter on the instruments necessary in the art of varnishing, and their use.

A general idea of the contents of this work may be obtained from the preced. ing analysis. The arrangement, upon the whole, is natural and satisfactory, the information copious and to be de pended on: but many parts would be essentially improved by rigorous condensation. The translator has suffered a few gallicisms to escape him, and, what is of more consequence, a few errors, either from inadvertence or ignorance: in one place he has put magnesia instead of manganese.

ART. VI. Researches into the Laws of Chemical Affinity. By C. L. BERTHOLLET, Member of the Conservative Senate, and of the National Institute, Se. Translated from the French, by M. FARRELL, M. D. Svo. pp. 220.

THIS is a treatise of the utmost importance, not only for the highly interesting facts which it communicates, but for the new light which it throws on a subject that has attracted the notice, and exercised the talents of the greatest chemists of the last and the present age.

The fundamental principle of Bergman, and which has been acquiesced in by all succeeding chemists, is, that all the substances in nature have a dispo. sition to unite with each other into binary or more complex combinations, the properties of which cannot be inferred from those of their constituent parts, and that the only way of effecting a chemical decomposition is, by presenting to the compound a substance whose affinity with one of the elements of the compound is greater than that which sub. sists between these elements themselves. In this case the former combination is destroyed, and a new compound takes place, consisting of one of the elements of the former compound united with the added substance, to the total exclusion of the other element. This he terms elective affinity, and, in order to determine its relative force in any two substances, he proposes to try if one of them can

remove the other from its combination with a third, and vice versa. He takes it for granted, that the body which has removed another from its combination, cannot in like manner be expelled by that other, and that both experiments will concur to prove that the first has a greater elective affinity for the third than the second.

This position is ably and successfully controverted in the work before us, in which it is demonstrated that there is no such thing as elective affinity, or a total transfer of one of the parts of a compound to a third substance; but that a partition of the base or subject of the combination takes place between the two bodies whose actions are opposed, in the ratio of their respective degrees of ener gy. He further shews that this partition is subject to be modified by the relative quantities of the bodies concerned, so materially, as in many cases to annul and even reverse the effects that would be produced by the relative energy affinity, other circumstances remaining equal. Having demonstrated these propositions by a detail of well contrived, simple, and convincing experiments, M. Berthollet then proceeds to consider the variations which the insolubility of bo

of

dies produces in the action of chemical affinity, and to explain the reason why a precipitate retains a portion of the body with which it was first combined. The modifications which are brought about by cohesion, crystallization, the elastic state, caloric, efflorescence, and gravitation, are then appreciated and explained. Having established the above rules, with their modifications, by examples from cases in which the action of three substances alone is concerned, the author then applies them to the more complicated cases of affinity, and shews that they hold equally good in these as in the former ones, and that the affinities of

compound bodies result from those of their constituent parts.

We consider M. Berthollet as having successfully proved in this valuable essay, the main point which it was his intention to establish, namely, that those cases which Bergman considered as proper decompositions, are in fact only partitions of one between two other bodies, in the compound ratio of their force and quantity. Here and there, however, he appears to have made use of rather ambiguous experiments, and to have drawn from them particular conclusions, which are scarcely justified by the facts.

ART. VII. An Essay on Chemical Statics, with copious explanatory Notes, and an Appendix on vegetable and animal Substances. Faithfully translated from the original French of C. L. BERTHOLLET, by B. LAMBERT. 8vo. 2 vols.

THE frame-work of these volumes is the researches on chemical affinity noticed in the preceding article. The author here extends his investigations to all the causes which can produce any variation in the results of chemical action, and treats of them considerably at length. The first part of this work is devoted to the consideration of the nature and laws of those forces which in the aggregate compose chemical action in general; and in the second part are developed the principal phenomena caused by the action of the various

chemical species upon each other. Properly speaking, therefore, this work may be considered as the philosophy of chemistry, as far as modern researches have hitherto extended. The importance of the subject, and the abilities of the author demand a careful and detailed examination into the merits of the book; and we trust that our readers will allow us to postpone to our next volume an investigation which cannot be entered upon at present without transgressing those bounds within which we are necessarily confined.

CHAP. XX.

MINERALOGY.

ART. I. Observations, chiefly lithological, made in a Five Weeks Tour to the principal Lakes in Westmoreland and Cumberland. 8vo. pp. 80.

JUDGING, perhaps, too hastily from the title page, we reserved this little volume for our mineralogical chapter. As a companiorto the scientific traveller

in these romantic regions it is, however, if not absolutely worthless, yet certainly of less than any assignable value.

ART. II. Organic Remains of a former World. An Examination of the Mineralized Remains of the Vegetables and Animals of the Antediluvian World, generally termed extraneous Fossils. B JAMES PARKINSON, Hoxton. Vol. 1st. containing the Vegetable Kingdom. 4to. pp. 480.

WE scarcely know how to charac. terize the volume before us. It displays extensive reading and a familiar acquaintance with cabinet specimens, at the same time that it betrays an entire unacquaintance with even the rudiments of modern geology, and a scanty knowledge of the mineralogical relations subsisting between the various species of minerals properly so called, and fossils, or the remains of organized bodies. One of Mr. Parkinson's objects, in publishing, was to render the study of fossils popular and attractive; he has, therefore, collected together as much entertaining matter as possible, and has adopted the epistolary form; a diffuse and vague manner of writing, well calculated indeed to attract the novice, but very unfit to inspire him with that rigorous preci. sion, without which all speculations on geological subjects are no better than idle vagaries of the fancy, better suited to the dreams of the poet than the deductions of the philosopher.

The four first letters, being preliminary matter, require no remarks and adrait of no analysis: in the fifth there is some geological matter which the author, for his own credit, ought to have omitted. "Mountains," says the author, "are with propriety divided into primitive and secondary;" thus entirely omitting the very important class of transition mountains. Again, in the list, for it is merely a list, of the different species which compose the primitive mountains, he totally omits two that are perhaps even more abundant, certainly

more important, than even granite, name. ly, micaceous and argillaceous schistus.

In the 7th letter Mr. Parkinson enters upon the proper subject of his work with a description of fossil trees. These he states generally to be found in almost every part of the world, but the authorities which he produces only prove it with regard to the alluvial strata in several parts of England and Ireland, in the neighbourhood of Modena in Italy, and in the deep sands of the low countries and the deserts on each side of Egypt. He also makes no distinction between trees that are merely buried without having undergone any chemical change, as those on the Lincolnshire coast, these which are still combustible but have undergone the process of bituminization, and those which are incombustible being completely silicified.

The 9th and three following letters describe, in a diffuse and entertaining manner, the natural history and other circumstances relative to peat and Bovey coal. The bitumens, amber, jet, cannel, and common coal, are then similarly noticed. We find, however, nothing that need particularly detain us till the 18th letter. This treats of bituminous fermentation, or that natural change which buried vegetable matter undergoes, and which is characterized by the formation of bitumen. This change, according to Mr. Parkinson, all vegetable matter is subject to, and therefore the extreme inflammability of bitumin ized wood, splinters of which are often used by cottagers instead of candles, by

no means proves that these trees, as some have supposed, were of the resiniferous kind. We believe, however, that Mr. Parkinson is somewhat mistaken here in point of fact. It is not the trunk but only the butt and roots of fossil trees that are applicable to the abovementioned use these trees, from their grain and texture, appear to be fir, and, what is more to the purpose, there are often found together with these other trunks apparently of oak, the roots of which are not sufficiently inflammable to be used for candles. One of the most striking and characteristic marks, however, of bituminization Mr. Parkinson has for gotten to mention, namely, that the ashes of vegetables which have undergone this change contain no potash. Although we notice these errors and omissions, yet we are well disposed to agree with the author in believing that vegetable matter when excluded from the air does really undergo the bituminous fermentation, in consequence of which it becomes more inflammable than before, and in capable of further spontaneous alteration. In common peat this change takes place only partially, because it is not perfectly excluded from the air, and not sufficiently compressed; but the lowest portion of very deep peat bogs (as has been verified by actual examination in Chat-moss in Lancashire) is of a black colour, a compact texture, abounding in bitumen, and very nearly resembling the softer kinds of coal.

Four letters are devoted to the discussion of the important question of the origin and formation of coal: the various hypotheses which have been proposed are fairly stated, and the objections to each of them are candidly and satisfactorily advanced. Mr. Parkinson's own opinion is, that all the present beds of coal were formed at the deluge: but the objections to his theory are at least as great as those which he has urged against the others. The regular and numerous alternations of the coal strata, each unmixed with and accurately separated from the others, evince that they must have been formed at distant intervals, and in a state of repose quite irreconcilable to the turbulence of a general deluge; not to mention that Mr. Parkinson has not explained how the uprooted trees of the ancient world were capable of sinking through the waters of the deluge.

The next subject which comes under

discussion is the mode in which the petrifaction of wood is effected The fact to be accounted for is this, viz. that the ligueous texture is most accurately preserved in petrified wood, at the same time that all the ligneous matter has been entirely superseded by earthy par ticles. Mr. Parkinson observes that timber which has been bituminized is of a much softer consistence and more porous than before: it is penetrated with water, and this fluid serves as a vehicle for the siliceous or calcareous particles, by the gradual deposition of which the whole mass becomes petrified. But, allowing this to be the fact, we do not see how it at all applies itself to the difficulty. Previous to the infiltration of stony matter, the wood, however altered, must contain a sufficient quantity of ligneous fibre to preserve the original texture of the substance, and it is very conceivable that these fibres may be entirely surrounded and all the pores filled by an infiltration of silex; but the lig neous skeleton, if we may use the expression, would still remain, and therefore there ought to be contained in silicified wood a much greater quantity of inflammable matter than we find actually to be the case; for it is not conceivable that the materials of a few grains of carbonated hydrogen and a drop or two of empyreumatic acid should be capable of retaining the minute and intricate texture of a piece of wood. One of the greatest novelties in this volume, though in our opinion by no means well founded, is the train of reasoning by which the author has persuaded himself to class opal among the secondary fossils of vegetable origin. The wood agate and wood opal display a ligneous texture, have a resinous lustre, and on distillation give a small quantity of empyreumatic liquor covered with an oily film. In pitchstone, though the ligneous structure is not visible, yet the resinous lustre is particularly striking, and this too on analysis is found to contain a similar proportion of combustible matter: finally, the opal itself. has somewhat of a resinous lustre, and yields about 5 per cent. of water and inflammable matter, therefore opal is only the end of a series of which bituminized wood is the beginning. But, by parity of reasoning, Mr. Parkinson might have added quartz also to his list of vegetable fossils, for quartz not unfrequently contains water and inflammable matter, and

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