times into large masses, reposing on the bottom. The great transparency of these rivers made the ice at the depth of fourteen feet quite evident. It had a greenish tinge, and looked not unlike moss. Sometimes it became detached from the bottom, and on rising to the surface it soon grew more compact by contact with the cold air, and floated away with the other flakes. It frequently happens that these pieces, in rising from the bottom, bring up with them sand and stones, which are thus transported by the current. Arrived at those parts of the river where, from the very little slope of the bed, the motion of the water is slow, and where the surface is sometimes frozen over, these floating masses collect, rub against each other, and get fixed; whence the inhabitants affirm that the river first freezes towards the lower part of the stream, and that from thence the congelation proceeds upwards till it reaches the higher and most rapid parts. Others assert that, where the water is shallow the ice begins to form at the bottom, and increases upwards by degrees till it gains the surface; thus forming a barrier to the ice-meers that come down, and contributing by this means to the congelation of the surface of the whole river. When the thaw sets in, the ice becoming rotten, lets fall the gravel and stones in places far distant from those whence they came. A striking example of the formation of ground-ice is mentioned by the Commander Steenk, of Pillau. On the 9th of February, 1806, during a strong south-east wind, and a temperature a little exceeding 34° Fahr., a long iron chain, to which the buoys of the fair-way are fastened, and which had been lost sight of at Schappelswrack in a depth of from fifteen to eighteen feet, suddenly made its appearance at the surface of the water, and swam there; it was, however, completely encrusted with ice to the thickness of several feet. Stones, also, of from three to six pounds' weight, rose to the surface; they were surrounded with a thick coat of ice. A cable, also, three and a half inches thick, and about thirty fathoms long, which had been lost the preceding summer in a depth of thirty feet, again made its appearance by swimming to the surface; but it was enveloped in ice to the thickness of two feet. On the same day it was necessary to warp the ship into harbour in face of an east wind; the anchor used for the purpose, after it had rested an hour at the bottom, became so encrusted with ice, that it required not more than half of the power to heave it up. usual On the 11th of February, 1816, the engineers of bridges and roads, residing at Strasburg, saw above the bridge of Kehl, that many parts of the bed of the Rhine were covered with ice. About ten o'clock, A.M. this ice became loose, rose to the surface, and floated. The thermometer in the open air stood at 10° Fahr.; the water in the river at every depth was at 32°. The ice at the bottom was only formed in places, however, where there were stones and angular projections. It was spongy, and formed of ice spicula. The overseers of the bridge stated that it never appeared on the surface until after ten or eleven o'clock in the morning. During the winter of 1823, Professor Merian carefully examined the bed of the canal of St. Alban, which conveys the waters of the Birse through the town of Bale. The stream is very limpid and flows rapidly. The bed is generally covered with pebbles. The Professor noticed that wherever the bottom exhibited any projections, there was a small piece of ice, which might have been supposed at a distance to be a re-uniting of This ice became disengaged from the bottom from time to time, and floated on the surface. It had all the appearance of the grund-eis of the Ger tufts of cotton. man watermen. M. Hugi, president of the Society of Natural History at Soleure, observed in February, 1827, a multitude of large icy tables on the river Aar. These were continu ally rising from the bottom, over a surface of four hundred and fifty square feet, and the phenomenon lasted for a couple of hours. Two years afterwards he witnessed a similar occurrence. On the 12th of February, 1829, at sun-rise, and after a sudden fall in the temperature, the river began to exhibit numerous pieces of floating ice, although there was no sign of freezing on the surface, either along the banks, or in shady places where the water was calm. Therefore it could not be said that the floating masses were detached from the banks. Nor could they have proceeded from any large sheet of ice farther up the river, because, higher up, the river exhibited hardly any ice. Besides, flakes of ice commenced soon to rise up above the bridge; towards mid-day, islands of ice were seen forming in the centre of the river; and by the next day these were twenty-three in number; the largest being upwards of two hundred feet in diameter. They were surrounded with open water, resisting a current which flowed at the rate of nearly two hundred feet in a minute, and extended over a space of one-eighth of a league. M. Hugi visited them in a small boat. He landed, examined them in every direction, and discovered that there was a layer of compact ice on their surface a few inches in thickness, resting on a mass having the shape of an inverted cone, of a vertical height of twelve or thirteen feet, and fixed to the bed of the river. These cones consisted of half-melted ice, gelatinous, and much like the spawn of a frog. It was softer at the bottom than at the top, and was easily pierced in all directions with poles. Exposed to the open air, the substance of the cones became quickly granulated, like the ice that is formed at the bottom of rivers. In the same year the pebbles in a creek of shallow water near a very rapid current of the Rhine, were observed to be covered with a sort of transparent mass, an inch or two in thickness, and which, on examination, was found to consist of icy spicula, crossing each other in every direction. Large masses of spongy ice were also seen in the bed of the stream, at a depth of between six or seven feet. The watermen's poles entered these with ease, and often bore them to the surface. This kind of ice forms most quickly in rivers whose bed is impeded with stones and other foreign bodies. It is unnecessary to give further instances of the recurrence of ground-ice; but it is time that we inquire concerning the cause of its formation. It may first be desirable to have a clear idea of the process of freezing, under the ordinary circumstances, and where the surface of still water becomes ice. Every one knows that if liquids of different densities be poured into a vessel, the heavy will sink to the bottom, and the light will remain at the top. This applies equally to different kinds of liquids, and also to one and the same liquid under varying temperatures. Liquids, like all other bodies, become more dense as their temperature diminishes. But there is a certain point in the temperature of water which presents a very singular exception to this rule. If water is taken at 50° Fahr. and gradually cooled, it becomes successively denser and heavier, until it reaches a temperature of about 3910, when it attains its greatest amount of contraction by cold. After this point it is a very curious fact that any further increase of cold causes it to expand, and consequently to become lighter, until it attains the freezing point, i. e., 32°, when a further and sudden expansion takes place, and it becomes ice. Were it not for this beautiful provision in the case of water, our lakes and rivers, instead of freezing gradually, would become almost in a moment a solid mass of ice, from which it is evident that the most serious evils would result. under the law which thus providentially regulates the congelation of water, the freezing of a lake or pond, or other body of still water, proceeds as follows. The first effect of the diminishing temperature of the air is to But cool the particles of water on the surface, and thus make them denser and heavier than the particles below. It naturally follows that the upper particles sink, and the lower rise to take their place. These in their turn become cooler and heavier, and sink likewise, being replaced by others. This successive cooling of the different layers of water goes on until the whole mass has attained the point spoken of above, i. e., about 3910, when it is at its greatest condensation. The continuance of the cold after this point, therefore, does not, as before, make the upper layer of water heavier, and cause it to sink, but on the contrary it makes it lighter, and thus keeps it at the surface. The expansion and consequent lightness of this upper portion of the water thus increases as the cold becomes greater, until it reaches the temperature of 32°, or freezing-point, when under ordinary circumstances, a layer of ice is formed. This coat of ice is in some measure a barrier to the effect of the atmosphere on the water beneath, so as to make it remain longer in a liquid state. But if the condensation of water went on regularly increasing up to freezing-point, the continual sinking of the colder portions would so affect the whole mass, that the whole would become, as we have already observed, a solid mass of ice. Surely there is ground for admiration and thankfulness in this exception to the rule by which all other liquids are governed; an exception which bears the stamp of beneficence, and affects in a very high degree the well-being of men and animals. Such is the process of freezing as regards still water: let us now consider the modifications which the motion of the water is likely to produce. The effect of this motion when it is rather rapid, when it forms eddies and flows over a rocky or unequal channel, is perpetually to mix all the layers. The law which regulates the congelation of still water, no longer applies. The water which is lightest does not always float on the surface. The currents are precipitated into the general mass, which is thereby cooled, and the temperature therefore soon becomes equal throughout. In a deep mass of still water the temperature of the lowest part can never descend below 39°; but when this mass is in a state of agitation, the surface, the middle, and the bottom, may be found at the freezing-point, or 32°, simultaneously. It becomes therefore necessary to inquire, why when this uniformity of temperature exists, and when the entire mass of liquid is at the freezing-point, congelation commences at the bottom, and not at the surface. In the first place, crystals are known to form more easily on unequal or pointed surfaces, than on any other, and therefore when the whole body of water has arrived at the freezing-point, it is not to be wondered at that the crystals begin first to form on the stones or other projections at the bottom of a river. Again, it is to be recollected that the motion of the waters has much to do in modifying the effect. At the surface this motion is very rapid and irregular in all those rivers in which ground-ice has been formed; while at the bottom of the river the motion is at least considerably diminished, so that although it may be sufficient to prevent the formation of compact ice, such as we see at the surface of still water, yet it may not prevent the gradual accumulation of that spongy kind of ice described in some of the foregoing examples, which could be easily pierced by the watermen's poles. This appears to afford the true solution of the difficulty respecting ground-ice; but there have been other theories on the subject which must not be withheld. That of Mr. Eisdale was founded on information which he had received from country people and others, whose operations depended on water-wheels, and whose interests forced them to attend to appearances, which might pass unheeded by others. The sum of their information was that the ground-ice was never formed except after a heavy rime, or hoar-frost. Hence Mr. Eisdale is disposed to offer the following explanation. The hoar-frost, which is congealed moisture precipitated from the atmosphere, and falling into the river when the water is cooled down to the freezing-point, cannot be dissolved. It retains in the water the very shape in which it descends from the air. When these small crystals fall on a deep unfrozen pool, the water being above the freezingpoint, the particles melt and are incorporated with the water; but in a shallow and agitated stream, almost the whole water is brought in succession into contract with the intense frost, and may thus be cooled down to the freezing-point to the very bottom of the stream, before even a pellicle of ice is formed on the stagnant pool. All the particles of hoar-frost, then, or frozen vapour, which fall on such a stream, will remain unmelted; and being tossed in all directions by the agitations of the current, will be brought into contact with the rocks or other substances projecting from the bottom, to which they will readily adhere, and form a nucleus for the ground-ice. Mr. Weitz conceives that the intensity and long continuance of the cold may freeze the soil to the depth of the bottom of the river, particularly where it is not deep, and that there the diminished velocity of the water permits of its congelation, particularly if there be any hollows where the water remains stagnant. So long as the congealed masses continue small with regard to the volume of water immediately above them, they adhere as if rooted to the bottom, and they rise bringing with them such gravel and stones as are found attached to them; whence Mr. Weitz concludes that not only does the current occasion a change in the bed of the river, by its erosion of the looser soil which it carries from one place to another, but that the ice which forms at the bottom of rapid rivers, in very cold countries, tends also to affect a change in the beds of those rivers. Mr. Farquharson has also a theory which is founded on the principle of the radiation of heat. Those parts of the bed of the stream which radiate most freely, become cooled most rapidly to freezing temperature, and hence ice is deposited in a manner somewhat similar to the deposition of dew, viz., the earth by radiation becoming colder than the atmosphere, condenses the vapour into drops of water; and so by the free radiation of some portions of the bed of the stream the water may become converted into particles of ice. In concluding our notice of this interesting subject, we may remark that although the theory of the forma tion of ground-ice is yet involved in much obscurity, the reader will be repaid the trouble of perusing the large number of facts which we have thus brought together from various sources; and should he be able to contribute any observations of his own they will be valuable, and still more so if given entirely free from theory. In their great designs men show themselves as they would wish to be; in small affairs they appear in their real characters. THE fruits of toil are the sweetest pleasures. WE should learn to think on principles in an age which cares only to remember facts. Ir is cheaper to educate two children than to feed a single vice. THE tricks of involuntary actions, as twitchings of the face, restless gesticulations of the limbs, biting the nails, &c., are generally at first occasioned by the want of sufficient bodily exercise to expend the superfluous animal power, but are also acquired by imitation. Hence long continued quiet, so often imposed in schools, should be avoided.— Encyclopædia. JOHN W. PARKER, PUBLISHER WEST STRAND, LONDON. The house itselfe doth showe the owner's wit, THE magnificent Palace of Theobalds, which owed its extent and importance to the progresses of Queen Elizabeth, stood in the parish of Cheshunt, at the distance of twelve miles from London, and a little to the north of the road to Ware. The first mention of the manor of "Thebaudes," as it was anciently called, was in 1441, when it was granted by the crown to the hospital of St. Anthony, in London. The origin of the name of Theobalds is not known; but it was probably given after some former owner, and the manor may have reverted to the crown at the suppression of religious foundations. Subsequently it passed through various hands until it was purchased, on the 10th of June, 1563, by Sir William Cecil, afterwards Lord Burghley. The original manor-house is supposed to have been on a small moated site still visible; but the building erected by Lord Burghley was on a much grander scale, and was in a state to receive the queen in 1571, when her majesty visited Theobalds, and was presented with a "portrait of the house." Lord Burghley was a builder on a magnificent scale, and his three dwellings are thus noticed by the author of his contemporary biography. He buylt three houses; one in London for necessity; another at Burghley, of competency for the mansion of his barony; and another at Waltham [this of Theobalds], for his younger sonne; which at the first he meant but for a little pile, as I have hard him saie, but after he came to enterteyne the quene so often there, he was inforced to enlarge it, rather for the quene and her greate traine, and to sett poore on worke, than for pompe or glory; for he ever VOL. XXIV. said it would be to big for the small living he cold leave his sonne. The other two are but convenient, and no bigges than will serve for a nobleman; all of them perfected, convenient, and to better purpose for habitation then manie others buylt by great noblemen; being all beautiful, uniform, necessary, and well seated: which are greate arguments of his wisdome and judgment. He greatlie delighted in making gardens, fountains, and walks; which at Theobalds were perfected most costly, bewtyfully, and pleasantly; where one might walk twoe myle in the walks before he came to their ends. The accuracy of this account is proved by a letter written by Lord Burghley to an intimate friend, in which he complains that some persons consider his therefore by saying that as to his old house in Westextensive building as a folly. He justifies himself minster, many had lately been built larger by far, both in city and country. Yet, he says, the building thereof cost him the sale of lands in Staffordshire, which he had from the good King Edward, and which had yielded him one hundred pounds yearly income. Then of his house of Burghley he declares that it is his mother's inheritance, who lives and is the owner of it, he being nothing more than the farmer or steward of it. Also that in that house he had set his walls upon the old foundation, and left one side of the walls just as he found it; and that doubtless his son would be able to maintain that house, considering that there were in that shire a dozen larger, of men under his degree. Yet in his house at Theobalds he is disposed to confess his folly in the expenses, " because," says he, "some of my houses are to come, if God so please, to them that shall not have land to mayntayne them: I mean my house at Theobalds; which was begun by me with a mean mesure, but 747 increast by occasions of her majesty's often coming; whom to please I never would omit to strain myself to more charges than building is. And yet not without some speciall direction of her majesty. Upon fault found with the small mesure of her chamber, (which was in good mesure for me,) I was forced to enlarge a room, for a larger chamber, which need not be envied of any for riches in it, more than the show of old oaks, and such trees, with painted leaves and fruit." The tourist Hentzner visited the palace of Theobalds when it was in its full beauty, and though he did not get a view of the apartments, his description gives some idea of the fashion of the grounds in those days. He speaks of the garden as being encompassed with water large enough for one to have the pleasure of going in a boat, and rowing between the shrubs." In this garden were labyrinths constructed with a vast deal of labour, trees and plants in great variety, a jet d'eau, with a basin of white marble, and columns and pyramids of wood. There was also a summer-house, in which were twelve figures in white marble, of the Roman Emperors, and in the middle a table of touchstone. In the upper part of this summer-house were large cisterns of lead, into which water was conveyed through pipes, so that fish might be kept in them. In summer time these reservoirs were used for bathing. Near this summerhouse was a second, joined to it by a little bridge, in which there was a noble table of red marble. Lord Burghley died in 1598, and Theobalds and the neighbouring estates fell into the possession of his son Sir Robert Cecil, who became Earl of Salisbury soon after the accession of King James. The king was sumptuously entertained at this palace on several occasions, and so great was his satisfaction, that he desired to become possessed of this noble residence, and to make it his principal place of abode. It was therefore agreed that Salisbury should give up his inheritance to the king, and should receive in exchange the palace of Hatfield, where in fact he soon built a mansion of still greater splendour, which has remained to our own times. The preamble to the act of parliament by which this exchange was ratified runs thus: "Whereas the mansion-house of Theobalds, in the county of Hertford, being the inheritance of Robert Earl of Salisbury, as well for situation in a good and open aire, and for the large and goodlie buildings and delight of the gardens, walkes, and park replenished with redd fallowe deere, as also for the neereness to the citie of London northward, and to his majestie's forest of Waltham Chase, and Parke of Enfield, with the commoditie of a navigable river falling into the Thames, is a place soe convenient for his majestie's princely sportes and recreation, and so commodious for the residence of his highnes court and entertaynment of forrayne princes, or their ambassadors, upon all occasions, as his majesty hath taken great likinge thereunto, of which the said earl having taken particular knowledge, although it be the only dwelling-house left unto him by his father, most willinglie and dutifullie made offer thereof unto his highness, with any such other his manors and lands thereunto as should be thought fit for his majesty's use, preferring therein his majesty's health and contentation before any private respect of his owne; which offer his majesty hath gratiously forborne to accept, without a full and princely recompense to the said earl," &c. Accordingly, on the 22nd of May, 1607, the possession of Theobalds was given up to the king, who afterwards made it his principal country residence. Windsor, Richmond, and Hampton Court were occasionally visited, but the monarch was evidently much attached to Theobalds throughout the course of his reign, and there at length he breathed his last on the 27th of March, 1625. Charles the First also made the palace of Theobalds his chief residence, and an interesting picture is still extant which represents the interior of the gallery at Theobalds, into which the King and Henrietta Maria are entering at a door, ushered by the brother Earls of Pembroke and Montgomery, each with his wand of office, the former as lord steward, the latter as lord chamberlain of the king's household. Waiting in the gallery stands the dwarf Jeffery Hudson, with three of the king's favourite spaniels; and a parroquet is perched on a balustrade. When the sale of the crown lands was determined on, Theobalds was at first excepted, yet afterwards its doom was fixed. The surveyors employed by Parliament to estimate its condition and value, reported that it was an excellent building, in very good repair, and by no means fit to be demolished; yet supposing the Parliament should decide on taking it down, their estimate of the value of the materials was 82751. 11s. This was too tempting a sum to be resisted, and therefore the greater part of this fine palace was taken down, and the materials sold to defray the expenses of the army. The survey made on this occasion affords a valuable and circumstantial account of the several buildings of the palace. It consisted of two principal quadrangles, besides the Dial-court, the Buttery-court, and the Dovehouse court, in which the offices were situated. The Fountain-court, so called from a fountain of black and white marble in the centre, was a quadrangle of eightysix feet square, on the east side of which was a cloister eight feet wide, with seven arches. On the ground floor of this quadrangle was a spacious hall, paved with Purbeck marble, the roof" arched over the top with carved timbers of curious workmanship, and of great worth, being a goodlie ornament to the same;" at the upper end was "a very large picture of the bignesse of a pair of stagges hornes seen in France." On the same floor were the Lord of Holland's, the Marquis of Hamilton's, and the chamber for the king's waiters. The king's presence chamber was a fine room on the second floor, "wainscotted with carved oak, painted of a liver colour, and richly gilded with antick pictures over the same, the seelinge full of gilded pendants hanging down, setting forth the room with great splendor; as alsoe with very large windowes, and severall coates of arms sett in the same." On the same floor were several other apartments, and likewise the gallery, one hundred and twentythree feet in length by twenty-one in width, richly ornamented with paintings. On an upper floor were the Lord Chamberlain's apartments, and near them were two walks on the leads of the building, each sixty-two feet in length, and eleven in width, which commanded a fine view. The queen's chapel and apartments were to the south of the central quadrangle. The prince's apartments were to the north. The with six lodges, at 15457. 15s. 4d. per annum. The park contained 2508 acres, valued, together 70007., exclusive of that marked for the use of the navy; deer were valued at 10007., the timber at more than the materials of the barns and wails were valued at 15707. 16s. 3d. After the Restoration the manor was granted to George, duke of Albemarle. The park and ruins remained with the crown until granted to William, duke of Portland, and his heirs. In 1763 they were sold to George Prescott, Esq., the ancestor of the present proprietor. The room in which James the First died, and a parlour beneath it, were standing in 1765, when the site was cleared for the present building. The only traces of ancient grandeur now remaining are, according to Gough, "a walk of abeles between two walls, a circular summer-house, and the traces of a park wall, nine or ten miles round, built by James the First.' The particulars thus given were diligently collected by a writer in the Gentleman's Magazine a few years ago, from whose account we have abridged as much as was necessary for our purpose. THE flattery of others would not injure us if we did not flatter ourselves. THE passions which the world praises and inspires are followed by its contempt; the virtue that the world censures and opposes attracts its homage.-MASSILLON. ON THE DURABILITY OF STONE BUILDINGS. II. AN EASY METHOD OF A DETERMINING WHETHER STONE WILL RESIST THE ACTION OF FROST. In the choice of a stone for building purposes it is of the utmost importance to be able to determine by a few prompt and easy experiments whether the proposed stone is capable of resisting the destructive action of moisture and frost. The means of ascertaining this were difficult and uncertain until M. Brard several years ago communicated his method to the Royal Academy of Sciences at Paris. This learned body having appointed a committee of their own members to inquire into the merits of M. Brard's process, and to make a report thereon, the united testimony of engineers, architects, masons, and builders from different parts of France was received, and proved so favourable as to its merits and simplicity, that the committee recommended the plan to public notice and general adoption. From their report we select a few details which hitherto, we believe, have not appeared in English. When water is converted into ice an increase in bulk suddenly takes place with such amazing force that it appears to be almost irresistible. This is the force which cracks our water bottles and ewers; splits asunder the trees of our forests; and destroys some of the stones of our buildings. But the action of frost upon stone is very gradual; it is confined to the surface, and when we see a layer of stone separated from the rock or the building, we see the result of the action of the frost during several successive winters, whereby the fragment is gradually thrust out of its perpendicular position, and at length falls. This natural process is repeated in our buildings: we rarely see squared stones split into large fragments by the action of frost except there be a cavity of some considerable size, in which a quantity of water can be collected. The usual action of the frost is at the surface, which is destroyed by the chipping off of small fragments in consequence of the adhesion of the materials of the stone being partially destroyed. All stones absorb water in greater or less quantities, and there is no rock that does not contain some humidity. The great difference between stones which is now to be considered is in their power of resisting frost. Stones of the same kind, nay stones from different parts of the same quarry, are acted upon very differently by frost; for while one stone soon begins to show the destructive effects of its action, another remains uninjured during many centuries. It will therefore be convenient in this article to call those stones, of whatever kind, which withstand the action of frost, resistant, and those which yield to its action, non-resistant. M. Brard's first idea in order to test these resistant properties in building stones was to saturate the stone with water, and then expose it to cold artificially produced; but this was found to be impracticable on a large scale, and the freezing mixtures and other means of producing cold were liable to act chemically upon the stone, and thus produce other effects than those of cold. M. Brard was then led to compare water with those numerous solutions of the chemist, which, under certain modes of treatment, crystallize. The expansive force of salts in crystallizing is very great, and he saw no reason why water should not be regarded as a crystalline salt similar in its nature to those saline bodies which effloresce at the surfaces of stones, and in time destroy them and even reduce them to powder. He therefore tried, in a very large number of experiments, the action upon building stones of solutions of nitre, of common salt, of Epsom salts, of carbonate and sulphate of soda, of alum and of sulphate of iron, and found that the stones cracked and chipped, and in many cases behaved precisely in the same way as when under the influence of freezing water. In the course of these trials sulphate of soda (Glauber's salts) was found to be the most energetic and active; and to be the best exponent of the action of freezing water. In order therefore to determine promptly if a stone be resistant or non-resistant, the following process was adopted. A saturated solution of sulphate of soda was made in cold water: the solution being put into a convenient vessel, the stone was immersed, and the solution boiled during half an hour: the stone was then taken out and placed in a plate containing a little of the solution. It was then left in a cool apartment, in order to facilitate the efflorescence of the salt with which the stone was now impregnated. At the end of about twenty-four hours the stone was covered with a snowy efflorescence, and the liquid had disappeared either by evaporation or by absorption. The stone was then sprinkled gently with cold water until all the saline particles disappeared from the surface. After this first washing the surfaces of the stone were covered with detached grains, scales, and angular fragments, and the stone being one that was easily attacked by frost, the splitting of the surfaces was very marked. But the experiment was not yet terminated: the efflorescence was allowed to form, and the washing was repeated, many times during five or six days, at the end of which time the bad qualities of the stone became fully established. The stone was finally washed in pure water; all the detached parts were collected, and by these the ultimate action of the frost upon the stone was estimated. The behaviour of various non-resistant stones under this process was remarkable. Some were found to have deteriorated in the course of the third day; others to have entirely fallen to pieces; those of which the power of resistance was somewhat greater, held out till the fifth or sixth day; but few stones except the hard granites, compact limestones, and white marbles, were able to stand the trial during thirty consecutive days. For all useful purposes, however, eight days suffice to test the resistant qualities of any building stone. Pure The explanation of this process is very easy. The boiling solution dilates the stone and penetrates it to a certain depth, nearly in the same way that rain water by long-continued action introduces itself into stones exposed to the severity of our changeable climate. water when frozen occupies a greater bulk than when fluid, and the pores or cellules of the stone not being able to accommodate themselves to the increased bulk of the water, great pressure is exerted between and among them, whereby a portion of the water is driven to the surface, and in doing so rends and detaches small portions of the stone. The same action takes place with the saline solution; it is introduced into the stone in a fluid state, from which passing into the solid it occupies a greater bulk, and a portion of it appears at the surface. The repeated washings have no other object than to allow the salt to exert its greatest amount of destructive action upon the stone. There is a striking analogy between the effect of congealed water and that of the efflorescence of salts, in the disintegration of non-resistant stones; namely, that pure water acts on the stones destructively only in a state of snowy efflorescence, which evidently proceeds from the interior to the exterior like the saline efflorescence; whilst water at the surface of the stones may freeze into hard ice without injuring them, just in the same way as salts, which may crystallize upon stones without exerting any injurious action. The experience of several engineers, extending as it does over several years, fully proves of a large variety of stones whose qualities were well known, that the action of M. Brard's process and that of long-continued frost exactly coincide. It is not the least interesting part of the inquiry to know that this process may be applied with perfect success to ascertain the solidity and resistant power of 747-2. |