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science, but who, from the nature of their occupations, are most likely to be purchasers of his work, and in whose hands we apprehend it will be found most extensively useful. His own avocations, and his familiar acquaintance with the science of chemistry, have enabled him to become intimately acquainted with the principles of those subjects on which he treats; and throughout the work he shews au anxious concern for the improvement of our domestic industry, which proves that the welfare of his country is an object of his constant solicitude. He neglects, therefore, no opportunity of pointing out the relations of the respective arts, with the established principles of chemical science, nor of suggesting inquiries or supplying bints, the investigation of which might lead to considerable improvements. The successful execution of such a plan as Mr.P. bas
proposed to himself, requires, indeed, accomplishments which are rarely united in the same individual; a profound acquaintance with chemical science, and anintimate knowledge of those arts which are dependant upon it, not as they are often imperfectly described in books, but as they are really practised in the recesses of our manufacturing establishments. Mr. P. has indeed had many valuable opportunities of acquainting himself intimately with the principles and practice of many of our domestic manufactures, and they have not been thrown away upon him. He has availed himself of them with diligence, and his work may be read with advantage by many, who would be discouraged from seeking information from works which are of a purely scientific character.
There is one feature of this work, which we must not overlook, because it contributes a great deal to relieve the uniformity of more formal details. Mr. Parkes has been very attentive on most subjects, in collecting what may be classed as historical notices, relative to the introduction and progressive establishment and extension of some of the important objects of chemical manufacture; a class of facts which are from their dature very liable to fall into oblivion, but which will merit to be preserved, as contributions to the history of our domestic industry, to which many an ingenious and active individual has essentially contributed, whose name will never find its way to that notice to which it is fairly intitled.
In the selection of the subjects of his Essays, Mr. P. states, that he has chiefly fixed on those which have been least examined by other chemical writers, and 'In all cases due atten'tion has been paid to the improvement of the manufactures of • the kingdom.'
The following are the subjects of the Essays on the Utility of Chemistry; on Temperature; Specific Gravity; Calico Printing; Barytes ; Carbon; SulVOL. V. N. S.
phuric Acid ; Citric Acid ; the fixed Alkalies ; Earthenware and Porcelain; Glass ; Bleaching; Water; Sal Ammoniac; Edge Tools. The fifth volume consists entirely of Additional Notes and Index.
On perusing this , enumeration, it will immediately occur to every chemist, that some of the essays scarcely come within the range of chemical science; and perhaps Mr. P. ought, on that account, to bave made the title page of his work more comprehensive and general, for certainly edge tools and specific gravity cannot be regarded as objects of chemistry. Yet those essays will no doubt be found valuable to a certain description of readers; and perhaps that on specific gravity will be the most generally useful of any in the work. We think, however, that the ample space occupied by the first essay, might have been more usefully iilled up; for the importance of chemistry, and its extensive application to all the purposes of life, are now so well known, and so correctly appreciated, as to make an essay on 'such a subject a much less appropriate introduction, than it would have been twenty or thirty years ago.
It is extremely difficult too, on such a subject, to avoid being perfectly trite, and where Mr. Parkes, has endeavoured to give novelty by deviating into less trodden paths, he has unfortunately ventured upon subjects which, being foreign to his pursuits, he does not understand. If there is any class of persons, for example, to whom an exhortation to study chemistry is superfluous, the medical profession is certainly that class, for chemistry forms a constant part of professional education, and it would be grossly incomplete without it. Mr. P. however, in the fulness of his zeal for his favourite science, has recommended it to their sedulous cultivation, for reasons which are less to be admired for their truth than their singularity. After exhorting the medical student, for example, to make bimself acquainted with the composition of the different salts, (a very superficial acquirement by the by, for any medical student,) be remarks, “This will inspire him with professional confidence; 6 and he will be as sure of producing any particular chemical
effect upon his patient, as he would if he were operating in his own laboratory.'
This appears to us to be perfect verbiage ; for we have yet to learn, nor does Mr. P. inform us, what resemblance or analogy there can be, between the operation of chemical substances on each other, and their effects on the animal economy. What chemical property of mercury or antimony, for example, will throw the least light upon the power of one in exciting salivation, and of the other in producing vomiting. Mr. P. however, has a remark on the subject, which he may perhaps think will make the matter plain and intelligible, though
me confess it does not do so to us ; nor will it, we apprehend, to bis Readers.
• Besides,' he remarks, the human body is itself a laboratory, in which the varied functions of secretion, absorption, &c. composition and decomposition, are perpetually going on: how, therefore, can he expect to understand animal physiology, so necessary to the practice of physic, if he be unacquainted with the effects which certain causes chemically produce ?'
Time has been, certainly, when, by oxygenating or decarbonizing the blood, or by neutralizing acids or alkalies which were supposed to be present in the fluids, physicians were to accomplish wonders; but these reveries have had their day, and are now as completely exploded as the visions of the alchemists. In fact, whenever men forsake the business of observation for the love of hypothesis, there is no end of human folly and extravagance. So far as relates to the arts in general, the importance of chemistry cannot easily be over-rated; but in the practice of medicine it is entirely subordinate, though still minently useful.
Mr. P. appears to us to place our own country in an unfavourable contrast with France, as to the proper appreciation and the facility of acquiring a knowledge of chemistry, to those who are preparing for the active duties of life. But in this we are ready to hope there is some misapprehension, for it is notorious that in Great Britain the means of obtaining an intimate and even profound knowlelige of chemistry, are within the reach of every person who, with competent intellectual capacity, has time and money to bestow upon the acquisition. The vanity of the French character inclines them to make more parade of their institutions than we do; but we believe our own will be found to embrace every solid requisite for instruction.
It is not our intention to give an analysis of each individual essay contained in these volumes, as such a plan would extend beyond all reasonable limits, nor are they very readily susceptible of being so treated; we shall therefore offer such observations as bave suggested themselves in the course of our perusal, trusting that we shall not be thought uncandid if our remarks should
appear to be confined in a great degree to those parts which are most open to animadversion, either from carelessness or inadvertency. In questions of science, accuracy is always highly iinportant, and is generally attainable by the exertion of reasonable diligence; and, in works of science, errors ough: therefore not to escape animadversion. Some of these we have noticed in the course of our perusal, and though not numerous, we think it right to point them out. In adverting for example to the advantages arising from a cultivation of cbear mistry, Mr. P. remarks,
· The making of cast steel which has been kept so profound a secret, is now found to be a simple chemical process, and consists nierely in imparting to the metal a portion of carbon by means of fusing it in crucibles with carbonate of lime, or by cementation withi charcoal powder, in a peculiar kind of furnace constructed for that purpose.' Vol. I. p. 33.
This is a very confused and erroneous statement of a fact in itself sufficiently simple. The first conversion of iron into steel, for manufacturing purposes, is effected, we believe in every instance, by the process of cementation, in which bar iron (generally Swedish) stratified with charcoal coarsely powdered, is exposed to an intense heat in a furnace constructed for the purpose. In this state it is called blistered steel. To convert it into cast steel, the bars of blistered steel are broken into fragments, and then fused in a crucible, with a small quantity of a flux which melts into a coarse kind of glass, which when fused floats on the surface, and prevents the action of the external air on the steel. When the steel is brought into a state of perfect fusion, it is poured into moulds, and it is then the cast steel of which Mr. Parkes speaks.
In the essay on temperature, p. 126, Mr. P. remarks that if water had the property of acquiring the same temperature from the sun's rays as the land, the evaporation in summer
would be excessive and detrimental ;' yet, in the succeeding paragraph, he observes that in hot climates, the seas, rivers, &c. are prevented from acquiring the temperature of the adjoining lands, by the evaporation which is continually going on at the surface of the water; so that after all, this difference of temperature is owing to the very causes of which the nonexistence is, in the former case, assumed as an instance of Divine wisdom in the adaptation of the world to the circumstances and condition of its inhabitants. The general views given of coinbustion, at p. 171, are singularly loose and unphilosophical.
The incipient combination of a body with oxygen,' it is remarked, increases its absolute weight. Thus by exposing melted lead to the action of the atmosphere, under a peculiar management, red lead is formed, and a ton of pig lead will yield 22 cwt. of red lead. But where complete combustion takes place, this increase is generally more considerable ; thus if 100 pounds of zinc are burnt in a proper apparatus, flowers of zinc will be formed, and the product will be 125 pounds.'
What precise meaning Mr. Parkes may attach to the term incipient combination,' in this particular instance, we do not profess to understand ; nor does the illustration convey to us any clear or definite explanation. The combination of the oxygen with the metal, is equally perfect and complete in both the in
stances adduced, though the phenomena which accompany the combination, are in some respects different, so that the one may be regarded as an example of combustion, which is not the case with the other. But the distinction as stated by Mr. P. does uint appear to us to have any foundation either in fact or theory, nor can such a view of the subject convey any clear and correct notions to the uninformed. In the same loose and careless manner it is asserted, that if lamp oil be burnt in a way that the product can be examined, it will be found that the whole is converted into pure water, and that every 100 ounces of oil will produce 130 ounces of water. Were this statement correct, it would necessarily follow that oil is pure hydrogen in a liquid form, which the most superficial acquaintance with chemistry will teach us it is not, but a compound of hydrogen and carbon; so that there must be a pretty considerable production of carbonic acid during the combustion, as well as of water.
In the essay on sal amoniac, Vol. 4, p. 378, Mr. Parkes gives an account of the process for preparing it, for which Mr. Astley, of Borrowstonness, near Linlithgow, (not near Leith, where Mr. P. places it,) has obtained a patent; and he is extremely anxious to recommend the adoption of this plan to those who, with skill and capital for the undertaking, have the advantage of residence near the salt works in England. Mr. P. remarks on this subject, that having acquired a knowledge of the fact that the bittern of the Scotch salt works is allowed to be used duty free for these purposes, the question immediately occurred to him
• If the inhabitants of one part of the empire are allowed an article which is capable of being used in our manufactories, duty free, why should not ihe same indulgence be universal in England and Ireland, as well as in Scotland ? Reflecting still more on this subject, and knowing that the riches of a country depend in a great measure on its producing within itself most of the articles required for its own consumption, I think it my duty to make this circumstance more generally known, in the hope that some competent person, possessing the advantages of capital, and a favourable locality of situation, would petition the legislature for leave to commence such an undertaking, and thus relieve the country from the necessity of sending into another quarter of the globe for a supply of this valuable and necessary commodity. If a company of persons accustomed to the manufacture of sal ammoniac, was established in the neighbourhood of any of the salt works in Cheshire, or near the salt pits in Droitwich, in Worcestershire, and could obtain permission from government to use the bittern which is produced at either of these establishments, and which af present is thrown away as an useless residuum, I am certain that such a company would be enabled to offer the article in question, much cheaper than the English Sal-ammoniac has ever yet been sold,