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application of thefe laws to the purpofes of life. As a fcience it explains to us a great variety of events, forming a part of the established courfe of nature, which we can neither direct nor change; fuch are, the effect of heat and light on the earth's furface, the production of clouds and rain; the action, of these and other things on the animal, vegetable, and mineral kingdoms. It is capable alfo of miniftering to our wants and luxuries, and teaches us to convert to the purposes of life, many things which nature prefents to us in a ufeless form. It is true, that the arts were practifed before chemiftry was raised to the rank of a science, and that they are still practised by men who are unacquainted with it. But fuch artists can only blindly follow a fet of rules. The arts are still far from perfection, nor can we expect them to reach it till artists become acquainted with chemiftry. The example of Meffrs. Watt and Wedgewood is fufficient to fhew us how rapidly manufactures and machines may be improved when scientific knowledge is happily blended with practical fkill. It may be faid, indeed, that theory fometimes draws men from the path of industry and leads them on to ruin. But it is abfurd to decry ufeful things because they may be abufed. Nor are chemical projects fo likely to end in disappointment as mechanical, unless the projectors be unwarrantably precipitate or deplorably ignorant. Our fuperiority as a nation depends a good deal on the unrivalled excellence of our manufactures. The French fully fenfible of the influence of chemistry on the arts. have zealously promoted it, and, in feveral instances, their inftitutions have been attended with very great fuccefs. Why fhould not our manufactures, already fuperior to those of other nations, advance ftill farther by the fame means?

Chemistry may be particularly ufeful in agriculture. This art, indeed, can fcarcely look for improvement from any other fource. Were the nature of foils properly explained and generally known, accidental difcoveries in agriculture might fpread much more rapidly than they poffibly can at present. What, for inftance, would it fignify to tell farmers that fuch a manure is admirably adapted for a loamy foil, while the word loam has one meaning in one part of the kingdom, and quite an oppofite one in another? The importance of chemistry in medicine is fufficiently obvious. Nor is it lefs ufeful to the metallurgift, or to him who extracts metals from their ores, who purifies them, mixes them together, and converts them into different ufeful inftruments; to the falt-maker or the manufacturer of potash, foda, common falt, vitriol, alum, faltpetre, borax, &c. to the maker of glafs and porcelain ; to the preparers

preparers of wine, beer, and fpirits; to the bleacher, the dyer, the printer, and to many other artists whose names might be mentioned. Notwithstanding the importance of chemistry to the arts it would be improper to confider its application to them in an elementary courfe; because fuch an application could not be understood till the fcience had been rendered familiar. In fuch a course it will be proper to begin with the confiderations of affinity, afterward heat, the gafes, which contain most heat, water, and alkalies, are to be fuccefively explained. The acids on account of their importance are to be introduced early. After this come the earths and metals; and Jaftly, the productions of the animal and vegetable kingdoms.

Such is the fubftance of the publication before us. It affords no mean fpecimen both of the author's acquaintance with the fcience and his qualifications as a teacher. His lectures will, we doubt not, prove of effential fervice to Manchester and if the author persevere, in the courfe which he has fo happily begun, he will in time prove an honour and an ornament to the science to which he has dedicated his attention.

The only parts of the lecture, with which we are not altogether fatisfied, are the definition of chemistry, and the line of diftinction drawn between that fcience and natural philofophy. Chemistry, according to our author, is the fcience whose object is to difcover and explain the changes of compofition that occur among the integrant and conftituent parts of bodies. If this definition be intended for thofe who are unacquainted with the fubject, as must be the cafe, we are afraid it will not communicate much information to them. What is a change of compofition? the phrase is technical, and cannot, therefore, be understood by those who are not previously acquainted with the science of chemistry. But, befides, the obfcurity of the definition we do not hesitate to confider it as inaccurate. For the primary object of chemistry is not to afcertain the changes of compofition, but to afcertain the compofition of bodies. It may be defined the fcience whofe object is to ascertain the fubftances of which bodies are compofed, and the nature of the law or property in confequence of which they are united. A complete account of the fubftances of which bodies are compofed, of their properties, and of the nature of their compounds, forms (if we may be allowed the term), the phenomenology of chemistry; just as a complete account of all the apparent motions of the heavenly bodies conftitutes the phenomenology of astronomy. The fcience of chemistry confifts in an investigation of the nature of that property common to all fubftances, termed affinity, in confequence of which they attract each other, and

remain combined with a certain force. The nature of this property can only be investigated by means of the phenomenology of chemistry.

The sciences arranged under the term natural philosophy, confift chiefly in the investigation of three properties of matter known by the names of gravity, electricity, magnetism. These properties produce certain motions in the bodies which poffefs them. The bodies either advance towards each other, or recede from each other with a certain force, or they prefs with a certain force on those bodies which prevent them from approaching or receding. Thefe three properties, therefore, are merely certain attractions and repulfions between bodies. The object of the different sciences of natural philofophy is to reduce these attractions and repulfions to measurement, to compare them all together, and to ascertain how far they may be all referred to one general law or property acting in different circunftances. The attractions and repulfions in natural philofophy produce fenfible motions. Chemical affinity may alfo be reduced to certain attractions and repulfions between the particles of matter; but these attractions and repulfions differ in this, that the motions which they produce are too fmall to be perceived by us; they are therefore infenfible. The object of the chemift ought to be to reduce them, if poffible, to meafurement. But this is a much more difficult task than in the natural or mechanical sciences, because the distances to be measured are incomparably more minute. But in some cases, and those luckily the most interefting, it is poffible, provided the chemift were only qualified for the task, which is not often the cafe; because chemifts have, in general, confidered their science as nothing but a collection of infulated facts, a mere heap of phenomenology depending upon principles neither capable of being defined nor measured. The attractions and repulfions in chemistry are evidently the fame in kind with those of gravity, electricity, and magnetifm; there must therefore be, at least, a ftrong refemblance in all. Now this very refemblance would produce important confequences in the hands of a chemift thoroughly acquainted with the writings of Newton, Boscovich, pinus, &c. and mafter of the mathemati cal calculus with all its modern improvements.

We have made thefe obfervations, in hopes of drawing the attention of chemifts to the most important part of chemistry. The phenomenology of the fcience is now fo far advanced, and it has been reduced by Lavoifier into fuch admirable order that almoft a fufficient ftock of materials for building the most durable edifice is in the power of every patient enquirer:

Black,

Black, like Kepler, has difcovered fome general laws, which will greatly facilitate the labours of any future Newton who fhall poffefs fufficient genius and induftry for a complete inveftigation of the nature of affinity.

We had almoft omitted to notice a mistake of our author, not, indeed, of much importance, but it has also been committed by others. Chemistry, he fays, is either a fcience or an art. Not fo. Chemiftry is always a feience, but many arts depend upon it for an explanation of their principles.

CHEMISTRY, MEDICINE, &c.

ART. X. An Effay on the Theory and Practice of Bleaching, wherein the Sulphuret of Lime is recommended as a Subftitute for Potab. By William Higgins, Profeffor, of Chemiftry and Minéralogy, at the Repofitory of the Dublin Society. 2s. Vernor and Hood. London.

HE bleaching of linen is a procefs very much connected with the commercial interefts of Britain, and still more, perhaps, with thofe of Ireland. Every one, therefore, who attempts to improve that process, or to facilitate the progress of those improvements, which have already been made, does a real fervice to his country. The prefent publication is undoubtedly of this kind. It is written profeffedly, the author tells us, for bleachers, and contains an account of bleaching in its moft improved state, as practifed in this country, together with fome very important improvements, which our author himself has made in it. The treatife is divided into five fections: we fhall give an abftract of them, omitting only thofe particulars which have been inferted for the fake of mere bleachers, being already familiar to every one who understands the rudiments of chemistry.

The firft fection contains a fhort account of flax. Ripe flax is compofed of four fubftances, namely, a thick cortex (the author means epidermis and porenchyma), a green coloured fap, the fibrous or flaxy part, and the woody matter. In order to feparate the other, fubftances from the flax, the plant is fteeped in foft water, till the fucculent part begins to putrify, which happens before the flax itfelf is affected. Hard waters injure the flax by caufing it to putrify too foon. The plant is then taken out of the water, and spread thin upon the ground, The united action of rain and dew, air and light, foon carry off the outer fkin and the pulp, and leave the woody part, now reduced to a dry and brittle ftate, furrounded by the flax. This woody part is afterwards broken to pieces by rollers and separated by fcutches, The flax is then hack

led

led to carry off the remains of the woody part which may have refifteft the fcutches, to split the fibres of the flax, and make them as fine as poffible, and to separate the fhort course flax or tow. It is afterwards fpun and weaved into linen. The reader who wishes for a more complete account of the preparation of flax, than has been given by our author, may confult the treatise of the Abbé Rofier.

In the fecond fection our author gives us an account of the old method of bleaching. When the linen comes from the loom it is charged with the weaver's dreffing, a pafte compofed of flour and water boiled together. The linen is fteeped in water for forty-eight hours, and then washed in order to feparate this dresfing. Linen thus treated is of a grey colour; and the object of the bleacher is to make it white. The grey colour is owing to a matter, combined with the flax, of a refinous nature, and confequently infoluble in water. To accomplish the feparation, the linen is boiled in water containing potash or foda diffolved in it, and therefore called an alkaline lie. Here the author gives us an account of the method of obtaining potash and soda, and of the different ftates in which they are fold to bleachers. But this we prefume is fo generally known that it would be wafting time if we were to transcribe it here. There are fome obfervations of our author concerning the purity of thefe alkalies which deferve

attention..

Potafb, or pearlab, always contains fome fulpbat of potafs: very often this falt is fraudulently mixed with the pearlath by the merchant even to the amount of one-fifth of the whole. Our author gives the following mode of estimating the quantity of impurities contained in pearlash, which we would recommend to the attention of bleachers before they purchase that article. Boil together for a few minutes three pounds of pearlath and two quarts of water, then remove them from the fire, allow them to ftand for twentyfour hours, and then decant off the clear liquor. Pour half a pint more of water on the dregs, and draw it off when clear. The falt, which remains behind undiffolved, being well dried and weighed, will give pretty nearly the quantity of impurities contained in three pounds of the pearlash.

Soda is often contaminated with common falt. Our author gives the following method of eftimating the proportion of this impurity. Boil the foda or barilla in thrice its weight of water, filter the liquor, boil what remains behind on the filter in half the original quantity of water, and again filter it. These two liquors are to be mixed, and fet by to cryftallize. If the barilla be good, cryftals will appear in five or fix days. But if not, the liquor must be evaporated down to one-third. Crystals will then appear confifting of carbonat of foda. The liquor is to be poured clear off thefe, and again evaporated down to one half. If much common falt be prefent it will make its appearance in cubic chryftals during this fecond evaporation. Thefe cryftals are to be feparated

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