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 ammoniac, 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 mùriate 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 information 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

was thrown about the shafts as a refuse article, he was enabled for some time to collect considerable quantities without exciting observation. What he thus collected, was sent privately to Liverpool, and from thence exported to Germany. This man was informed by the agent at Liverpool, that it was employed in the manufacture of Porcelain, and though any information on the subject which he was likely to procure, must be liable to considerable uncertainty and suspicion, yet this hint may deserve the attention of the manufacturers of this costly production, in our own country, if this earth does not already enter into the composition of their Biscuit ware. Mr. P. learned that the inhabitants of this sequestered district had found by experience, that this mineral was a poison to their cattle and poultry, probably long before its deleterious effects on the ani mal economy were known to physicians and physiologists.

The essay on sulphuric acid contains an interesting account of the progressive improvements by which the manufacture of this important chemical agent, has been brought to its present state of perfection and extent. The tedious and expensive mode of obtaining it by distillation from the sulphat of iron, or copperas of commerce, was first superseded in this country by the ingenious Dr. Ward, who formed the sulphuric acid by the direct combination of its constituent principles, though the process does not appear to have been his own invention. That gentleman, however, obtained a patent for this process, by which sulphur and nitre were burnt together in large glass globes, of the capacity of forty or fifty gallons each, each globe having a proper quantity of water introduced into it, to absorb the acid as it was formed during the combustion. By this means, he had for some time the monopoly of the manufacture of this acid, until the celebrated Dr. Roebuck, of Birmingham, introduced the capital improvement of conducting the combustion of the mixture of sulphur and nitre in chambers constructed of sheet lead. This plan at once removed the great source of expense in the breakage of the glass vessels, and speedily reduced the price of the acid to about one fourth of its former cost; and thus contributed in the most direct and essential manner to its extensive introduction into various processes of the arts, from which its former high price must have nearly excluded it.

The first establishment of the leaden apparatus was effected at Birmingham, by Dr. Roebuck in conjunction with the late Mr. Samuel Garbett; and this original work still continues to be carried on. The situation of this work however, and the difficulty and danger of transporting it at that period, (about 1746,) when our internal navigation was so incomplete, confined the consumption of the acid principally to the neigh