we confess it does not do so to us; nor will it, we apprehend, to his 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 knowledge 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 have 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 important, and is generally attainable by the exertion of reasonable diligence; and, in works of science, errors ought 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 che, 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 merely in imparting to the metal a portion of carbon by means of fusing it in crucibles with carbonate of lime, or by cementation with 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 combustion, 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 not 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 the 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 at 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,

and at a rate which would effectually prevent the importation of sal ammoniac from any part of the East.'

Mr. P. has here fallen into a very important error, which it is the more necessary to notice, that persons inclined to enter on speculations of this kind, may not be misled by the prospect of advantages thus delusively held out from the want of more correct information. In Scotland, salt for domestic purposes, is obtained from sea water by evaporation; and there is consequently a very abundant residuum of the nature which Mr. P. has stated. This residuum however is not homogeneous; it consists of sulphat of magnesia, which we believe goes under the appellation of bittern, and which when crystalized and purified, is the Epsom salt of commerce, and the muriate of magnesia, which being uncrystallizable, goes under the name of oil of salt, and is the material made use of by Mr. Astley in his process for preparing sal ammoniac. But it happens very unfortunately for Mr. Parkes' recommendation, that at the salt works in Cheshire and Worcestershire, so far from these substances being thrown away as a useless residuum, they do not occur at all; the brine from which the salt is obtained not containing any sulphat of magnesia; and of the muriate of magnesia a quantity too small to separate during the evaporation so as to form a residuum. That this is the case of the salt works at Droitwich, we know from personal inquiry.

Mr. Horner, in his account of the salt springs at Droitwich, published in the second volume of the Transactions of the Geological Society, estimates the proportion of muriate of magnesia, at only 1 76 grains in each pint of brine, or .07 per cent. of the whole saline ingredients; so that it does not bear the proportion to the marine salt of 1 to 1000. We have not at hand the means of stating the proportion of this salt in the Cheshire brine, but we believe it is equally pure as that of Droitwich. Hence, the salt manufactured at these places is dry and clean, and does not deliquesce at all; while the Scotch salt is quite the reverse, and always requires to be kept in a dry, warm situation, to be at all fit for use There are we believe a few situations on the English coast where sea water is evaporated for the making of salt, as at Lymington, and there the recommendation of Mr. P. might be adopted with advantage; but it does not apply at all to the salt works in the interior of England, so far as our acquaintance with them goes Whether the proprietors of the works on the coast, are prohibited from availing themselves of the advantages which Mr. P has pointed out, by the excise laws, we do not know; but the manufacture of Epsom salt is carried on there we believe to a pretty considerable extent. We apprehend, however, that these establishments are not of sufficient extent to make the question of

any importance in a national point of view, as it regards the manufacture of sal ammoniac; though certainly there can be no equitable reason assigned for imposing limitations on the capital and ingenuity of one part of the Empire, which are open and free in others.

We have pointed out these instances of carelessness and inaccuracy, not in the spirit of uncandid severity, but because the last is especially too important to be passed over without notice, and because we are persuaded Mr. P. would be himself the first to wish for their correction. The more pleasing part

of our duty remains, to point out by a reference to a few of the essays, the species of information, which Mr. P. has selected for the gratification and instruction of his readers. The essay on barytes contains a good deal of curious and useful informa tion on the native salts of that earth, more especially its carbonat. It is well known, that if the carbonat of this earth could be procured in sufficient quantity at a cheap rate, it might be introduced into the arts with great advantage, especially for the purpose of obtaining soda by the decomposition of common salt. Mr. P. a few years ago, visited the principal mines from which it has been obtained, situated near Chorley, in Lancashire; and he gives an interesting detail of the information which this visit enabled him to produce. A century ago it seems these mines were worked with success for the lead ore with which they abound. The carbonat of barytes being the matrix in which it was imbedded, was left in the mine as a useless production. The late Sir F. Standish, however, the proprietor, discontinued the working of these mines about five and twenty years ago, from no other cause as it would seem, than that he was defrauded by the persons in his employment, and from that time they have been abandoned entirely. About that period the nature and properties of the barytic carbonat, were investigated and made known; and our present knowledge of the useful purposes to which it may be applied, would now augment the value of the produce very considerably. It is on this account much to be regretted, that the present proprietor is not induced by these considerations to have them worked again; for it does not appear from the information obtained by Mr. P. that any deficiency of lead ore had been felt before the working was given up.

It would seem, however, that even at that period, the carbonat was known to be applicable to some useful purposes in the arts. Mr. P. was informed that about thirty years ago, these mines were visited by two Frenchmen, who collected and carried away a pretty considerable quantity of this mineral; and that subsequently a man who occupied a small farm on the estate, had been engaged in a clandestine commerce with it, for, as it