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between Europe and America, Britain should become the magazine of the universe.
• Let all foreign grain, then, be allowed importation at all times under the King's lock, upon the principle of an entrepôt, there let it lay the pleasure of the owner for a market. We are better fituated for it than Holland was ; if any demand should be made from the southern markets, our own ships can be got out from our ports at all seasons of the year,
which is not the case in Holland. • We speak from fact and our own knowledge, that, was such a principle adopted, the corn-dealers in the north of Europe, and those who have long been in the trade in other quarters, would cheerfully avail themselves of it. But it is not only from the Baltic that considerable supplies of grain would be sent to such an entrepôt, but from America ; their conscious security of the country, although they were seeking for markets, would always induce them, as they now often do, to touch at Ark or Falmouth, to learn the state of the European markets, or call for orders. Great numbers of the American merchants, and they are mostly bold and enterprizing, would at once send their produce here for a market, and take our manufactures in return.
• From foreign grain being stored in this manner, would arise a certain advantage to the country. If, whilst our wafte lands are getting into cultivation, any failure of our crops should take place, the stock in hand might be brought into the market by the regulations of the present, or some more judicious act. Monopoly, which is so much cried down, would not exist in the face of a large unknown stock; and if the price advanced under these circumstances, it would rise from an actual defici. ency in the country, to supply which we should then always have a stock in ftore : for want of such a Itock, prices rapidly advance here, and the advance is anticipated abroad ; so that it colts us enormous prices unne. ceffarily created.' P. 511, 512.
The short view which we have given of the contents of this book, leaves us but little to add upon its general merits. The author is never profound or philosophical in his views ; nor does he seem to have powers for clear or comprehensive reasoning. He is often vague, redundant, desultory, and inconsistent; and his diction is mean and clumsy. But he is a man of great experience, and no small practical sagacity; and has produced a book more suited to the wants and to the capacity of ordinary traders, than the
greater part of those which are founded upon juster maxims
J. Murray ART. X. Essays, chiefly on Chemical Subjects. By William Irvine,
M. D. F. R. S. Ed., Lecturer in Materia Medica and Chemistry in the University of Glasgow ; and by his son W. Irvine, M. D. 8vo. pp. 490. London, 1805.
It has often been regretted by those who have paid attention to
that interesting part of chemical science, which relates to the more abstruse doctrines of heat, that the theory proposed by the late Dr Irvine was never fully brought before the public. He himself gave no account of it, but in the chemical lectures which he delivered in the University of Glasgow ; and although the heads of it have been stated by Dr Crawford, who was well qualified to do it justice, the statement was only incidental, subordinate to his own views, and, of course, unaccompanied by those details and illustrations which its author could have best given it, and which were necessary on'a subject in some measure obscure. From this cause, although the outline of the theory has been generally known, its real merits have scarcely ever been fairly appreciated; it has often been misunderstood, nor has it ġet had that rank assigned to it in chemical science to which it appears to us to be entitled.
Having long been accustomed to consider this theory of the distribution of heat in bodies, and of its absorption during liquefaction and vaporization, as the most philosophical that has yet been suggested, we turned to the perusal of this work with much curiosity and expectation. We have still to regret, however, that we have not the author's own statement and illustration of his peculiar views, or have them only in a very imperfect manner. In the preface, we are informed that Dr Irvine's manuscripts, at least in what relates to this subject, were in no respect fit for publication, and were even in such a state, that no satisfactory account of the experiments and theory could have been compiled from them. To Dr Irvine, junior, the editor of this publication, there only remained the alternative of availing himself of them as far as possible, in explaining and illustrating what he knew from other sources of his father's opinions ; and although this is not precisely what those interested in the discussion would have wished, nor what we are persuaded it would have been the wish of the editor to present to the public, it is but justice to him to acknowledge, that he appears to be intimately acquainted with the subject, that he has bestowed on it much attention; and has conveyed to us some interesting information on his father's experiments. If some tincture of enthusiasm may, as he remarks, be expected in a son, who treats
of his father's labours, we have not observed any want of candour, or any undue partiality to the doctrines he defends.
Dr Black was the discoverer of the important truth, that when a body is heated to the point at which it begins to melt, it is not sufficient to communicate to it merely a little more heat to produce an entire change in its form ; but that, as the change proceeds, it absorbs a large quantity of caloric, which has no effect in increasing the temperature of the fluid, and which exists therefore in the body in this new form, in a state not discoverable by the thermometer ; and again, that when the liquid is heated to the point at which it passes into vapour, a similar absorption of caloric, unaccompanied with any augmentation of temperature, takes place. The heat existing in this state Dr Black termed latent, to distinguish it from sensible heat, or that by which the temperature of the body is raised,
In speculating on this important truth, Dr Black supposed that the caloric which thus disappears is the cause of the change of form ; that the latent heat existing in a fluid or vapour, is that which
preserves it in these states; and that the vapour cannot be condensed, nor the liquid congealed, without this latent heat being withdrawn.
Dr Irvine viewed these phenomena in a different light; he regarded the absorption of caloric, not as producing, but as arising from the change of form. Dr Black had established, from an experiment related by Boerhaave, the important general conclusion, that in different bodies the same temperature is not, as we might perhaps be disposed to imagine à priori, produced by the same quantity of heat or caloric, but that one body will require a very different quantity from that required by another; and that, therefore, at any given point in the scale of the thermometer, different bodies, in equal quantities, whether estimated by weight or volume, contain very different quantities of this principle; a fact which came to be expressed by saying, that different bodies have different capacities for heat.
Now, it occurred to Dr Irvine, that the absorption of heat which attends both the melting of a body, and its transition into the elastic state, might be owing to an alteration in its capacity. When a solid becomes liquid, or a liquid is converted into vapour, he supposed that its capacity or power of containing heat may be enlarged ; and if this happen, the necessary consequence must be the absorption of a quantity of caloric to keep up its temperature to the point in the scale of heat at which the change takes place. By saying that the capacity of a body is enlarged, nothing more is meant, than that, at a given temperature, it is capable of containing more caloric than formerly. "If such an enlargement happen,
therefore, a quantity of caloric must be absorbed, by which the temperature will not be raised : this portion of caloric will disappear, or will not be discovered by the thermometer, and the phenomena of what Dr Black termed 'Latent heat, will be produced,
Dr Irvine“ was not disposed to consider the entrance of what is called latent heat into bodies as happening upon different principles from those which always, direct the operations of caloric upon matter. Though ready to admit the discoveries of Dr Black, in all their extent and importance, and no man thought more highly of them, as none more fully appreciated their value, he imagined that latent heat was only a case of what occurred in every affection of bodies by heat, and that the caloric existed there precisely in the same way as at other times, and could be discovered by the same tests which at any time give notice of its presence. Not willing to descend to a dispute concerning a term, he was ready to admit the phrase, latent heat, as the expression of a new and curious fact, though not without some modification in the exact sense to be attached to it. He was accustomed to observe, that the latent heat followed as a mere consequence of his peculiar view of the operations of caloric; by this affertion, not claiming any share in the honour of discovering the existence of latent heat, but expressing that his theory being granted, the previous discovery of Dr Black fell into it as a part of a whole.
p. 50. 51. The question then to be decided was, does this enlargement of capacity happen during these changes of form ? To ascertain this, Dr Irvine made a number of experiments; and one of the most valuable parts of the present work is the account that is given of the manner in which these experiments were performed, as, with regard to this, chemists had hitherto no precise informacion. It had even been supposed that they had been made in a manner which would have rendered them altogether inconclusive, by mixing ice and water together at different temperatures. The ice would thus be melted, and a quantity of caloric would disappear. This might be owing to a change of capacity; but it might also be owing to the caloric entering into a more intimate combination. To say that it was owing to the former cause, would have been merely taking for granted the point in dispute. It was necessary, therefore, to render the experiment conclusive, that the capacity of the solid should be ascertained while it remained folid, and that of the fluid while it was fluid, and that in the progress of the experiment neither should change its form. The difficulty of executing such an experiment with accuracy must be obvious; and with regard to ice it could be performed only when the temperature of the atmosphere is very considerably below 32° of Fahrenheit; a cold which in our climate does not often occur ; and when it does, is not of long duration. The subject, it ap
pears, had engaged the attention of Dr Irvine for a number of years ; and it would have been much to be regretted, had all record of his experiments been lost. A general account, however, sufficiently satisfactory, has fortunately
been preserved. The method employed, was to determine the respective capacities of ice and water by the medium of a third substance, which could first be mixed with the one at temperatures below 32°, and afterwards with the other at temperatures above this, and thus afford indications which would not be ambiguous from any change of form.
• He found the capacities of some suitable bodies, as river fand, or iron filings, and compared them with that of water in the usual manner. This being done, he used the same body to examine the capacity of pounded ice formed from distilled water, or of snow. The temperature of the room and vessel was, in his experiments, always either 32° or below it ; most commonly confiderably under 32°. He then took a known weight of snow or ice of a known temperature, in a vessel of which the capacity was determined by experiment. Upon this he poured a certain quantity of river fand washed, or iron filings of a certain temperature, with as much rapidity as poslible; the new temperature was observed after stirring, and allowance was made for the heat gained or loft : the temperature of the mixture was frequently 19", 20°, 25°, 16', &c. So that in a room where the air was below the freezing point, the accuracy of the result could not be affected by the formation of any water : till there are many sources of inaccuracy remaining. But in Dr Irvine's hands, the capacity of ice always turned out to be less than that of water. In all his experiments, which were very numerous, and repeated with care for many succeeding years, he arrived at results approximating to each other, and concluded, to use his own words, that from the mean of all his trials, the capacity or relative heat of water to that of ice is not in a ratio greater than 5 to 4 or 10 to 8.
• In like manner, Dr Irvine extended his theory to all other bodies whatever, and in some cases determined, and in all inferred, that it is a general law of nature, that the capacity of all solids for heat is increased by fufion, and that of all fluids by vaporisation. This law, the exiftence of which was not before even suspected, must be considered as a highly important observation, as all generalisations of facts are to be regarded, and that whether the theory which is attempted to be deduced from it be ultimately established or overthrown.' P: 55-57.
Do these experiments then prove the truth of Dr Irvine's theory? Of this, we conceive, no just doubt can be entertained. Did the absorption of heat, which attends the melting of a body, arise from that heat entering into any peculiar state of combination-were the peculiarity in the relation of the body to caloric limited, as Dr Black in his speculations conceived it to be, to the actual liquefaction, it is obvious that the liquid, after it was