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JUNE 1, 1811.
[5 of Vol. 31.
A> Ions it theft wbo write are ambitious of making Conrerrs, and of ching their Opinion* a Maximum of Influence and Celebrity, the raoft exter.fiveiy circulated Mii'ccliany will repay whh tbe grnteGt Xflcft th«j Curieftty of thole wbo read cither for Amulemenc or Intrusion. JOHNSON.
THE SUPPLEMENTARY NUMBER. Hilherta our Supplementary Number has been partly occupied with imperfect critical accounts o/'cut rent English literature, eonftssediy and necessarily compiled from
■ thou fallible, partial, and corrupt mediums, the periodical anonymous Reviews,
■ aided by occasional originality; in future, however, it is proposed to substitute in - place of those wholesale criticisms, interesting characteristic extracts from the principal works published within the half year, adapted at once to gratify our readers, .to qualify them to judgeofevery work for themselves, and to stimulate them to puv
■ chase those possessed of evident merit. The Supplement published on the first of August, will be compiled on ihiiplan; and, to assist our design, we shall feel ourselves obliged to authors and publishers, who will accommodate us with the loan of books published between Michaelmas and Lady-day last.
Pimlico, May U, 18J1.
For the Monthly Magazine. On the application of Mineralogical
and CHEMICAL SCIENCE to the SELECTION of Stone, for the purposes of DURABLE ARCHITECTURE.
r*¥^HE remains of ancient architecture, X which prove the greatness and splendour of states and governments that have long since ceased to exist, whilst they impress the mind with a melancholy conviction of the mutability of empire, excite also a kind of religious veneration for the edifices which have endured, amidst such y-eat and various changes in human affairs, and have seen a. long series of successive generations perish from the earth. When we compare these monuments of antiquity with the preudest structures of modern times, we are forced to acknowledge the superior skill, or science, with which the materials of the former were selected. Alany of the most splendid works of our celebrated architects are hastening to decay, in, what may be justly called, the very infancy of their existence, if compared with the date of public buildings which remain in Italy, in Greece, in Egypt, and the East. Ibis is remarkably the case with the three bridges of London, Westminster, and Blackfriars; the fdundations of which speedily and visibly began to perish in the very lifetime of their founders. Tire destruction of ancient architecture has been chiefly occasioned by the ravages of wars, and the desolating hands of superstitious barbarians; the decay of modern buildings, MoNiiLLY. Iuaq. No. ?13.
is owing to the want of mineralogical science in the selection of the materials, by which they were sentenced to perish at an early date. None of them will rival in duration the temples of antiquity, and remain two thousand years, or more, after the ruin of the state, the august monuments of its former greatness. This may with certainty be predicted from the perishable nature of the stones of which they are built; they are rapidly decaying, and require constant renovation and repair.
Perhaps the following remarks on the selection of materials, for the construction of public buildings, may not be undeserving attention at this time, when two new bridges are to be built from London and its vicinity, to the southern side of the Thames. The most important quality in stone, for purposes of architecture, is durability, or the property of resisting the action pf moisture, change of temperature, vegetation, air, and light. It is also required, that the materials of bridges, and many public works, should be capable of resisting the effects of vibration and impulse. The most careless observer can scarcely have avoided noticing, that many kinds of stone decay much s'loner than others. It is not only in' stones of different kinds, that iho power of resisting decay is variable; even in stones of the same kind, and brought from the same place, n considerable difference in this respect is found to exist; but the principles on which the proper selection of building-stoue, sriould be * F made made, hat been little understood or attended to. During a few months' residence in the metropolis, I was induced, by the nature of my minernlogicat pursuits, to pay some attention to the different stones of which the pavements and public edifices are constructed. On walking into the court of Somersethouse, after some weeks of dry weather, I was particularly struck with the appearance of the columns on the left band, facing the west. The stones, in three columns, were some of them entirely coated with soot, when the stones above and below were perfectly white. In other parts, n white stone was between two black ones, and the division of colour as distinct as if the one had been painted white and the other black. These stones were all equally exposed, and the variation of colour could not be explained by their situation. At first I conceived, that this difference of colour might be occasioned by some substance entering into the composition of the black stone, that had a chemical affinity for ammonia, which is contained in soot; but, on examining soma of the stones that were within my reach, I found that those which were covered with soot, had a hard, smooth, surface, and the white stones were evidently decaying. The particles on which the soot had fixed, were fnHen off, and had laid bare the natural colour of the stone, as perfectly as if they had been recently scraped with a chissel. In other parts of the building, I observed the visible decomposition of the stone, by moisture, particularly in the upper part of the alto relievo figures.
This edifice, (ike most of the modern buildings in the metropolis, is constructed of Portland-stone; a peculiar kind of lime-stone, which I shall afterwards more particularly notice. It is evident, how. ever, that this stone which is considered of the same kind, and comes from the same place, varies much in its property of durability.
When the same' stone is constantly exposed to the action of water, the difference in its qualities of resisting decay is more apparent, as is evident from an inspection of London, Blackfriars, and Westminster, bridges, at low water.*
* The stones of Westminster bridge appear to have been selected with more knowJedge, as they are much lest decayed than thme of Blacjcjjws j th* architect wit • YrSRcbman.
The best kind of Portland stone is ill suited to resist the decomposing effects of water, the two former of these magnificent bridges, constructed at so much expence, are perishable monuments of the neglect of mineralogical science.
In stones of the argillaceous genus, more striking instances of rapid decay occur. I have seen stones of this kind, in their native beds, or quarries, some 'hundred feet under the sarl'ace of the earth, so extremely hard, that they resisted the point of the pick-axe, and could, only be removed by blasting with gunpowder; yet, when the same stone was exposed to the air for a few months, it became soft and shivered into small pieces. The cause of this sudden decay, I shall afterwards explain. It rarely happens that builders or architects have any acquaintance with mineralogical and chemical science, to enable them to anticipate the changes «liich will be effected in the materials they select, by the action of the agents to which they are to be exposed. The loss and disappointment which this ignorance has occasioned in the construction of many public works, is well known.—A remarkable instance of this kind lately took place at Paris. A gentleman was walking with an eminent mineralogist in one of the newly-erected public edifices; they were pleased with the appearance of some large columns in the interior; when the latter had examined them more closely, he predicted, from the nature of the stones, that they would perish in less than three years, About ten months after, the gentleman happened to pass the same place, and observed the stones of these columns were shivering so rapidly, that workmen were then engaged in replacing them; which had become necessary to secure the roof. In forming the tunnel of the Huddersfield canal, which is three miles in length, the workmen in one part bad to cut through a bed of stone of considerable extent, so hard that they were obliged to remove it by blasting. It appeared so compact and firm, that it was thought unnecessary to wall and arch the passage; but, in a few months after the access of nir to it, it shivered and fell in; and the removal and repair occasioned much delay and expense. It was :\ dark compact argillaceous stone, containing oxyd of iron, and resembling some kinds of basalt; but its shistose or slnty structure was soon apparent, ann*' it became as soft as the bituminous shale which accompanies coal. Some kinds of
stone become harder, by exposure to the atmosphere. An inquiry into the causes of decay in different kiinf) of atone, and also1 in stones considered of the same kind, may not be undeserving the attention of the public.
To ascertain these causes with precision, it will be necessary to attend, first to the external character of stones, and _4T the qualities and proportions of the earths of which they are composed; and, secondly, to the decomposing or disintegrating effects of the agents to which they are to be exposed.
The four earths which form the principal juafct of all building-stones are silex/oT the earth of flint, clay, lime, and magnesia. The substances which sometimes enter into their composition, and alter their quality, are oxyd of iron, water, and carbonic ncid: the other earths, or metals, are generally in too small quantities to deserve the attention of the architect. The qualities which these (our earths communicate I shall afterwards state. The most important external characteristics uf stone for building are, compactness of texture, hardness, degrees of frangibility, and specific gravity. Compact texture, or closeness of grain, is always an advantage in stones of the same kind; for it is evident, that a porous stone will be more exposed to the action of air, or moisture, than a denser one of the same kind: but compactness of texture is no test of excellence m stones of different kinds, for chalk is frequently more compact than many kinds of durable sand-stone. Hardness is also an important character in comparing varieties of the same species of stone, but it will not serve as a test of durability in stones of a different genus, mi account of the different effects which different agents have upon them. The hardness of natural or artificial substances i* no direct proof of their strength; glass, which is harder than iron, is more frangible than soft limeatone. In compound stones, which have a crystallized texture, we frequently find the parts extremely hard, but the adhesion of the parts to each other very slight, as in some kinds of sand-stone.
Great specific gravity, or weight, is a proof of excellence in stones of the same kiiid, unless it arise from a combination with water, or the presence of iron, which is a circumstance deserving great attention; as iron, when in combination with •tones, is acted upon by air and water, which occasions their decay, Some
basalts, which are extremely compact, ponderous, and hard, striking fire with steel, contain more than 35 per cent, of iron, and are soon decomposed at the surface, when exposed to the atmosphere. In general, specific gravity, where it does not arise from the absorption of water, and the presence of iron, or other :n«. tallic earths, may be considered as a quality indicating excellence for purposes of architecture. No stones, except those which contain the earth of stroutian, or harytes, weigh three times as heavy as an equal bulk of water, unless they are combined with some metallic substance, which is generally iron. The specific gravity of few stones, except foreign marbles, exceeds 3.80, unless some iron be present.
The quality of the three earths, silex, clay, and lime, is essentially distinct; but there are scarcely any stones that can be employed in architecture, in which they are not more or less combined together; communicating their character according to the proportion in which they combine. Hardness is a distinctive character of stones, into which silex enters in a very large proportion. Silex being insoluble in water, and all the acids, except one of rare occurrence, silicious stones are, of all others, the most durable, and best suited for tha foundation of bridges, piers, and docks. Silicious stones are frequently com. j, pounds, containing two, three, or more, substances, united together in a granular or crystallized form.
Granite is composed of quartz, felspar, and mica. The quartz contains mora than ninety parts of silex, the felspar sixty, and the mica, which is generally in the smallest proportion, about forty. The grains, or crystals, though distinct, are as firmly imbedded and united to each other, as if they had been melted together, Granite is not only extremely hard, but is also very infrangible, resisting the effects of violent percussion. Some kinds of porphyry, which contain crystals of felspar, imbedded in a silicious base, are as hard, and still less frangible than granite. Many of the edge-stones of the foot pavements in London, are of porphyry, which appears to he of a very durable kind, and might probably be used to great advantage in forming the foundation and base of the arches of the two new bridges, to be erected over the Thames. Granite is found chiefly on the western side of our island; there is, how. ever, a range af low granite mountains, at Charnwond forest, in Leicestershire. The granite is chiefly used for paving in the neighbourhood; it is small-grained, or what some mineralogists would call, secondary granite; and others sunite as it contains small crystals of hornhlendp. Its specific gravity I found 2.77. It is extremely hard, and is worked by blasting. If it can he raised in blocks of sufficient magnitude, it might be employed with great advantage in constructing the foundation of the new bridges; as it is only one hundred miles distant from London, from whence there is direct carriage by water. It is,.! believe, the most durable •tone that can be found in any great quantity at the same distance from the metropolis. At the same place is procured another stone, resting upon the granite; it is a species of greenstone, and hornblende porphyry, containing small crystals of felspar, in a basis chiefly of hornblende. The workmen informed me, it is broken with more difficulty than granite; it is not so hard, but is very infrangible. Its specific gravity I found S.U8. It contains some osyd of iron, like other stones of this species, which may perhaps render it improper to be used, where it can be acted upon by water; but it has every appearance of being a very durable stone, and might deserve the attention of builders, where great strength of materials is required. In silicious sand-stones, the coarseness or fineness of the grains is of less importance than the substance in which they are imbedded. Those which have a Lasis of ferruginous clay, are soft and perishable; but when the basis itself is of a silicious kind, the stones are almost equally durable with granite. The upper strata of many of the highest hills in Yorkshire and Derbyshire, are of this kind, which Mr. VVhitshurst calls a millstone grit. It is of a finer-grained stone, of the same kind that Kirkstall Abbey, near Leeds, is built. Though tlje Abbey is a ruin, the stones which remain are little decayed. After tiie lapse of six hundred years, they preserve their angular sharpness, and the impression of the chissel, as fresh as if they had been recently worked. There is n quarry of. this stone in the neighbourhood; and I have observed some of the stones in the London docks, are of a similar kind. Some silicious sand-stones appear to be of alluvial formation, and have their parts so imperfectly cemented, that they are unfit for the purposes of architecture; of this kind are the rocks on which the town
of Nottingham is built; and the red-sand rock of Cheshire. The former may be considered.more properly as indurated gravel, intermixed with rounded quartz pebbles; but, though it is too loose to be applied to purposes of architecture, it may be excavated to a considerable extent, without the necessity of supporting the sides and roof. The granite of Charnwnod forest, and the loose sandrock of Nottingham, are not more than twenty miles distant, but tl.ey may be considered as forming the two extremities of the scale of aggregate silicious stones, from ,the very hardest to the softest kind. Argill, or clav, is never found pure in any kind of building-stone. It is soft, smooth, and unctuous to the touch, and will absorb more then 2J times its own weight of water; and, as Mr. Kit-wan has observed, it communicates, in some degree, these properties to stones, if it is combined in a proportion of from 30 to 30 per cent. In a greater proportion it destroys the qualities of silicious stones. Many argillaceous stones contain a considerable quantity of iron, not perfectly oxydated. When exposed to the atmosphere, they speedily decay. It is in stones of the argillaceous kind, that the greatest caution and mineralogical knowledge are required, in the selection for purposes of durable architecture. I have seen a hillock at the mouth of a lead-mine, supporting a luxuriant vegetation, which a respectable miner informed me he had twenty years before blasted from a compact bed of toadstone, or basalt, that resisted the pickaxe, and no soil had been since thrown Upon it. An instance of this kind was the occasion of an action at the last York assizes, between the proprietots of the Barnsley canal, and the e/igineer. On the part of the proprietors it was contended, that the hill through which he had to cut a tunnel, was a soft marble. On the part of Mr. Piukerton it was stated, that, though the part exposed was now soft, it was, when first opened, a very hard and compact rock, extremely expensive and difficult to work; and the truih of this statement he offered to prove, by perforating any part of the hill where .the stone had not before been laid hare lo the action of the atmosphere. The argillaceous sand-stone which accompanies or lies over coal, is used for buildings in coal countries, as in some parts of the West Riding of Yorkshire; but it is not suited for public buildings, or works intended to be durable. Stones
of the calcareous genus, comprise nil the various marbles and limestones. These ore generally more free from a (mixture with oilier earths, than stones of the si. licious, or argillaceous kind; anrl their relative degrees of excellence for purposes of architecture are more easily ascertained by their external character. Besides pure lime, they contain from 45 to 50 per cent, of carbonic acid and wafer. Lime when pure is soluble in five hundred times its weight of water; and, even when united with carbonic acid, it is in a les< certain degree soluble in river waters, owing to the minute portion of difleient acids, which is generally contamed in them. On this account they are ill suited to form the foundations and piers of bridges, or t > be employed in the construction of works exposed to the action of the water. The durability of marbles and lime-stones might, I believe, with some certainty he determined by their relative degrees of hardness, and by observing the time required to dissolve on equal cube of each kind of stone in marine acid, of the name strength, diluted with five times the quantity of water at the same temperature. The sediment remaining will also determine the quantity of silex or clay with which the lime js combined. Magnesia enters into the composition of some lime-stones in the proportion of two-fifths, and renders the softest stones of this kind less soluble, in acids than the hardest marbles, on which account it will be necessary to ascertain by.chemical experiments, whether the slowness with which lime-stone is soluble, proceeds from the presence of magnesia; but I believe it will also be found that a mixture of this earth, where it occurs in lime-stone, not only renders it less soluble in acids, but communicates to it a degree of durability which is not to be found in other lime-stones of the same degree of hardness. The high comparative degree of preservation observable in the exterior pf York Minster, and other public edifices which are built of this stone, may serve to prove its excellence for purposes of architecture.
Portland Stone is a peculiar kind of lime-stone, which some mineralogists call roe-stone. When examined with a magnifying lens, it will be found to contain a number of small round globules, resembling in appearance the roes of fishes, imbedded in a calcareous basis, from whence it derives its name. It also contains fragments of shells, and minute calcareous crystals. It varies in its opa
lines of hardness and compactness, and in its properties of durability, as may be observed in many of the public edifices in London, which are built of this stone. In the construction of St. Paul's, some attention appears to have been paid to the selection of the stones for the exterior; which are more perfect than those in many buildings of a recent date; but they are evidently perishing in the upper part of this magnificent structure.
Portland-stone contains carbonate of lime, united with a small portion of sites and clay. Its solution in diluted muriatic acid gives a dark-blue precipitate, with the Prussian alkali, indicating the presence of oxyd of iron, to which itowes its brownish tint; but the quantity of iron is too small to affect its quality for the use of the architect. It burns to a white lime, losing more than eight parts in twenty of its weight, during calcination. According to Professor Jameson, roestone is never used for architecture, on account of its speedy disintegration; but his observations appear to have bijen confined to the varieties of this stone in Germany, and inapplicable to those in our own island. Two stones culled by the same name, from different situations, are seldom exactly similar in ull their properties; which indeed rarely happens with stones from different layers of the same bed. And where strata of calcareous stone are separated by other kinds of stone, the upper and lower strata, almost invariably differ in hardness and specific gravitv; on which account it would be very desirable, that a mineralogical examination of stones should be made in their native quarries, and that those which arc intended tor the external part of buildings, should be judiciously selected from the others. Of nil stones of the calcareous genus, there cannot be a doubt that compact marbles, which run receive the higl*sr. degree of polish, would be the most beautiful ami duinhle for the exterior of buildings,; but I heir scarcity in ibis country prevents their application to this purpose. Alabaster, which is composed of lime, united with sulphuric acid, from its beauiy and the facility with which it c.vn be worked, le used for ornamental, architecture and sculpture; but the solubility of this stone renders it ill-suited to resist the agency of water.
Dr. Watson relates, that he suspended two ounces of this stone in a pud of water for forty-eight hours, changing the water several times, and found that it