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instant of their birth. A beam of light now bursts from all fides; opinions, the offspring of an extravagant imagination, are consigned to oblivion; and elegance and stability are given to the fabric. But to collect facts is the labour of the dull compiler; to introduce order and symmetry is the work of genius and discernment.

We are led into these reflections by the perufal of the treatise before us. Our expectations are indeed disappointed. The production is below mediocrity. To originality of matter, to clearness of method, to beauty of order, it has no pretenfions. The language is slovenly and inaccurate, and the ara' rangement is uncommonly confused. The author plumes himfelf in being able to comprise the whole system of chemistry in a single volume. But small is the 'merit of so paltry an: abridgment. . The work is divided into two books : the first confiders general chemistry, the second particular chemistry. The author's definition of chemistry conveys no idea whatever : “ As a

science, its object,' says he, is to estimate and account the ( changes produced in bodies by motions of their parts, which " are too minute to affect the senses individually.' It is feldom that we meet with a sentence so obscure. Does he mean that the parts of bodies are too minute to affect the fenses; or that their motions are too minute to affect the senses? To what does the word individually refer? Is it meant that one fenfe alone receives the impression; or that one part, or one motion, produces the sensation. If the sentence has any meaning at all, it admits of four different applications. Besides, the word eslimate, in the present case, conveys no idea. The author proceeds, in a cursory manner, to mention analysis, synthesis, elective attractions, &c. At once we are hurried into the midst of the science; and the effects of heat are stated before the term is explained. • Heat expands folids, then renders them fluid, and afterwards (converts them into vapour; and these changes succeed each & other according as the intensity of the heat is rendered greater.' This is, no doubt, very laconic; but unfortunately the last clause of the sentence is nonsense.-In the second chapter, the author begins more deliberately. He makes the common remark, that the word heat is employed either to denote the sensation itself, or the cause of that sensation. The effect is supposed by some to be produced by the internal vibration of the particles of bodies; by others it is imagined that the agent is a certain subtle fluid which is diffused through the universe. Some bodies are more easily heated than others in the same situation, and are therefore termed better conductors of heat. Whatever be the cause of heat, its general effect is to enlarge the dimensions of bodies;

and

' and this expansion is found to be nearly proportional to the addi

tions of heat that are made. It has a tendency to an equal diffusion ; but it does not follow that all bodies of the same teme perature contain it in equal quantity; for some are more suscepa, tible of its effects than others. Hence the distinction into abfolute and relative heat. The densities of heat in different bodies in a similar exposure, are termed their capacities for heat. The capacity may be estimated from the change of temperature ob. served in mechanical mixture. Some philosophers have ascertained it by the quantities of ice, which different bodies, at the fame temperature, were able to melt. Water has a greater capacity for heat than ice, and steam a ftill greater than water. Hence arise the effects of evaporation and frigorific mixtures.

In Chap. III. Mr. Nicholson treats particularly of the thermometer, and gives directions for the construction and examination of it, and concludes with the rules for converting the degrees of Farenheit's into those of Reaumur and Celsius. He next explains, in a cursory manner, the various operations of

chemistry; calcination, fusion, cementation, digestion, distilla' tion, &c. and gives a short description of the more common ap

paratus. Our author then considers the mode of operating upon elastic fluids, describes the eudiometer, and Dr. Nooth's elegant apparatus for impregnating water, and states the im. provements which have been made in collecting the aerial products in distillation.

The next chapter is allotted to the consideration of weights and balances; a subject of great importance in nice chemical experiments. The delicacy of a balance is indicated by the slowness of the vibrations of the beam. The accuracy which has been introduced is quite astonishing. Mr. Bolton had a balance, which, when loaded with a pound, would turn with the tenth of a grain. One made for Dr. George Fordyce is affected by the me the weight; and the balance lately made by Mr. Ramsden for the Royal Society can ascertain a weight to the seven millionth part! The first part of the work concludes with some remarks upon the inertia of matter, gravity, elective attraction, solutior, crystallisation, &c. The author seems fond of the filly notion of the polarity of particles.

Mr. Nicholson proceeds, in the second book, to consider particular chemistry. He speaks of light as if the doctrine were founded entirely upon conjecture. It is, generally ( taken for granted,' says he, that light is a substance, or ? an emanation of particles of prodigious minuteness, which are

projected in right lines, with extreme velocity, from luminous bodies; and that they are repelled from all bodies at ENG. REV. VOL. XV. MAY 1790,

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• certain distances, and at less distances attracted, so as to proma • duce all the effects of reflection, refraction, and infection, in « the rays they compofe,' What a strange inconsistent medley of words and ideas! He then flightly mentions the notion affixed by the chemists to the word phlogiston, and Mr. Kir. wan's supposition that it is the fatne with hydrogenous gas. He next contiders combustion, the absorption of oxygen gas, the production of this gas, the nitrous test, the hydrogenous gas, the composition of water, and the effects of the eoliple. After this rapid view of the aerial fluids, he descends to treat of the primitive earths. He considers the alkalis, relates the process for the manufacture of glass and soap, and mentions the general properties of the mineral, vegetable, and animal acids. Mr. Scheele described a process for extracting foffil alkali from sea falt. Mr. Turner triturates litharge with water and half its weight of common falt, till it assumes a white colour, and then allows the mixture to stand for fome hours. The alkali is disengaged, and the marine acid unites to the calx of lead, and forms a yellowish green pigment, the sale of which is the principal object of the manufacturer. He next surveys the metais; mentions the division into perfect and imperfect, their calcination, crystallisation, solution, &c. and the opposite theosies which have been formed on these subjects.

Mr. Nicholson now returns to examine more minutely what he had before slightly touched. He details the properties of vitriolic acid and fulphur, and their various changes and combinations. This acid is generally obtained by burning a mixture of eight parts of sulphur with one of nitre, in a large vessel lined with lead, and containing a small portion of water to absorb the fumes.-He next considers a very interesting fubject, that of the nitrous acid; the formation of nitre beds, the extraction and purification of the salt, its deflagration and detonation, the composition of gunpowder, the pulvis fulminans, &c. the distillation of the acid, its formation, its effect upon animal substances and the

essential oils; and fightly explains the opposite theories which · have been offered. The marine acid occupies the next chapter.

The fca contains, he fays, between the tropics, from an eighth to an eleventh of its weight of falt. This is a mistake; for in no part of the world does the quantity exceed one twentieth. He relates the various methods of extracting the salt, and of cryftallifing it. The distillation of the acid, and the various compounds that it forms, are next considered. The oxygenated marine acid is of a singular nature ; and its property of instantly deftroying calour, has been directed with advantage to the bleaching of wax and linen. The power of aqua regia to dis-, folve gold is probably derived from the extemporaneous pro-

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duation of oxygenated 'marine acid. Our attention is next turned to the carbonic gas, and those substances and processes which contribute to its formation, the calcareous matters, fermentation, and the combustion of charcoal. Its acidulating quality, and its combination with earths and alkalis, are men. tioned. The acid of borax comes next to be considered ; its production, its puriication, its analysis, its properties. The acid of amber has lately been examined, but its properties are not remarkable.

Mr. Nicholson next treats of the phosphoric acid, a subjeet on which so much light has lately been thrown. It abounds in animal substances, it occurs in the cruciform plants, and it is even found in the mineral kingdom. It is sometimes combined with the ores of lead; and to iron it communicates the cold-Jhort quality; an unfortunate circumstance for the manufacturers of this country. Both phosphorus and its acid are now obtained with ease from bone ashes. The acid is always formed by the union of oxygen with the phosphorus, and may be procured in greater purity by the inflammation of the phosphorus, by the spontaneous decomposition arising from exposure, or by the action of nitrous acid. Phosphorus dissolves in oils and ardent spirits, and communicates to them a lumi., nous appearance. The solution in some of the essential oils has the property of spontaneous inflammation, when exposed to the air. A stick of phosphorus, plunged into the solutions of gold, silver, copper, and other metals, is gradually covered with a brilliant metallic sheath. The phosphoric acid combines with all the alkalis. Other acids have lately been examined, the theory of which is scarcely yet ascertained. The acids of arsenic, molybdena, and turgoten, obtained from the ores.

Mr. Nicholson then proceeds to the confideration of the metals. The malleability and ductility of gold is quite astonishing. It is unalterable in the strongest heat of our furnaces. It is, however, volatilised in the focus of powerful burning-glasses, and partially calcined. The electric explosion converts it into a purple calx. Gold is foluble alone in aqua regia and oxygenated muriatic acid. By a careful evaporation the folution yields fine crystals of a topaz colour. It is precipitated by the earths and alkalis, and even by the addition of martial vitriol, and forms a yellowish or purplish powder. The precipitate made by volatile alkali or fal ammoniac is termed aurum fuimi. nans, because, when gently heated, it explodes with astonishing violence. The volatile alkali, which unites to the calx, is fuddenly decomposed ; the oxygen combines with the hydrogenous gas and forms water, while the azotic gas is instantly extricated. Hence the vitriolic acid, oils, æther, &c. which detach the volatile alkali, destroy the fulminating quality. If gold be 'Y 2.

precipitated

precipitated from aqua regia by means of tin, we obtain the purple powder of Calsius, which is used as an enamel. Gold is not acted upon by nitre or the alkalis. It dissolves, however, in the liver of sulphur. It combines most readily with mercury. Hence the process of water-gilding.-Silver comes next to be considered. It is fixed in the heat of common furnaces; but, exposed in the focus of a powerful lens, it fumes and vitrifies. It is tarnilhed by the influence of the air ; and the scales which are formed, during a course of years, upon silver images, are found to be a compound of that metal with sulphur. Silver dissolves in all the inineral acids. The solution in nitrous acid , yields thin crystals, which are called lunar nitre; and these, when

fused, form lunar causic. The affufion of marine acid produces luna cornea, which is difficultly foluble, and is thrown down. Heated with fixed alkali, it yields the purest silver. A curious discovery has lately been made by the ingenious M. Berthollet. He diffolves pure silver in pale nitrous acid, and precipitates it from the solution by the addition of lime-water. He dries the calx by exposing it to the air for three days. He next stirs it in ä solution of caustic volatile alkali till it becomes a black pow. der; he then decants the Auid, and leaves it to dry. This is fulminating silver. The experiment requires to be conducted with the utmost caution. The flightest agitation occasions an instantaneous and dreadful explosion. The theory is the same with that of fulminating gold. Mercury separates silver from its solutions extremely slowly. The precipitate assumes fanciful forms, and fometimes resembles the ramifications of a tree; and hence is termed by the alchemists arbor Dianæ.— The new metal, platina, is next considered ; it is the densest of all the metals. It has, in common with iron, the fingular property wi welding. It is precipitated from the folution in aqua regia by sal ammoniac,

which distinguishes it from the other metals. It is not affected · <by the Pruffian alkali; and this circumstance is the foundation

of the method of feparating it from iron, with which it is commonly combined. Platina forms with copper a compound that admits of a fine polith, and is not subject to tarnish; and hence it has been ufed for the mirrors of reflecting telescopes. Mr. Nicholson next mentions the properties of mercury, its various compounds and preparations. Lead is the next in order. It is precipitated from its folutions by the liver of sulphur. If Fead be heated with charcoal and phosphoric acid, the acid is converted into phosphorus, and combines with the metal. The compound, in its appearance, resembles lead. By the assistance of heat, lead decomposés fal ammoniac, and disengages the vola"tile alkali. Litharge, fused with common falt, unites to the marine acid, and forms a yellow pigment. A mixture of eight

. . parts

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