1840.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



199 



As to the hardness or induration of the white limestone ; I gave 

 a kind of dynamic unit of the labour or ordinary force em]]loyed in 

 boring into it for the purposes of blasting, viz., that the force of two 

 men striking with hannners were able to sink into the white limestone 

 at the rate of one foot in depth in half an honr, fjampers 1^ of an inch 

 in diameter, hammers about three pounds weight) then the elements 

 employed were the momentum of the hammers, united to the power 

 of the arm, and the time; this is the common labour or force em- 

 ployed. It may be asked what is the amount of it ? But to answer 

 this is rather difficult, because one element cannot be perhaps exactly 

 determined, which is the force of the arm united to the momentum of 

 the hammer; but the induration of any rock may be reached or mea- 

 sured in a more exact form; in boring with heavy iron cylinders, and 

 merely working with the simple element of the descending force of 

 the gravitating mass of the iron bar ; and the amount of this force may 

 be estimated by the number and length of the descending strokes, using 

 the following formula. The momentum of a body falling is the mass 

 or weight multiplied by the square root of the height it has fallen 

 through and by s-0-21. 



The number and length of the strokes, and the time occupied would 

 be the measure of the force employed in sinking to any depth in any 

 kind of rock, and this indeed might be used as a standard of compari- 

 son to measure the amount of the manual labour employed in boring 

 through all the varieties of rock. 



Sir John Robison, the ingenious secretary of the Royal Society of 

 Edinburgh, observes with great truth that much depends on the shape 

 and condition of the cutting point of the bar employed in boring, and 

 also on the goodness of the steel and iron. In operations of this kind 

 approximate results can only be obtained, and tliese should never be 

 determined, regarding any particular rock, without numerous experi- 

 ments on all the varieties it would present. 



The hardness or induration of rock, as well as its strength to resist 

 crushing by weight are matters of high importance to the engineer ; 

 but has any scale yet appeared to measure the amount of these two 

 properties ? 



The weight which rock can s.ustain without crushing or fracture, 

 may I think be taken as the amount of its strength. And the measure 

 of its induration or hardness to resist perforation may be determined 

 by the momentum of the descending strokes of an iron bar, and the 

 ■ time employed. The law of the relation of strength compared to 

 hardness may be then traced from these results in all the various kind 

 of rock strata. 



What are the causes of the disentegration of the white limestone ? 

 i. e. the chemical agents which act so powerfully in decomposing its 

 structure? To what cause does it owe its great hardness ? If it be 

 ascribed to heat from its close vicinity to the trachyte formations, the 

 lava of the more ancient revolutions, and which I admit is a natural 

 inference ; but then on the other hand, I ask to what cause can be 

 ascribed the high induration of the secondary limestone which covers 

 so extensively the plains of Ireland, so far removed from any kind of 

 volcanic remains or formations? 



Indeed since' the discovery of the carbonic acid gas contained in 

 limestone by the illustrious Dr. Black, the science of chemistry has 

 achieved but little practically in unfolding the chemical properties 

 which give induration to the various strata of the older series, and 

 among which are to be seen the most beautiful, as well as the most 

 imperishable material for engineering works to be found on the globe. 

 Some of these rocks have been wrought at periods so extremely remote 

 that there is difficulty sometimes even to fix the epoch, yet some of 

 them carry on their surface the sharp unimpaired lines of the tool 

 after a lapse of more than three thousand years, and this is fully proved 

 and illustrated in glancing at the granites and sienites employed intlie 

 construction of those surprising monuments of Egyptian antiquity, 

 which have astonished all ancient and modern travellers. 



calcareous spars, consist almost entirely of liniR in chemical combination witli 

 carbonic acid or fixed air, the fonner constituting someH hat less than threc- 

 lifths, the latter somewhat more than two-fifths of their \\hole weight. 

 Hence in scientific language they are called earljonates of lime. The car- 

 bonic acid or fixed air may he expelled by heat, or Ijy the addition of any 

 other acid : in the latter case an effervescence takes place, and this elicc- 

 vescence is a very distinctive character of calcareous carbonates, (page 2.) 



■' Marbles and limestones are with respect to their chemical analysis the 

 same, they dilier only in their uses and external character. — (Page 3j, Kkld's 

 Mimratogy, 



Limestone chalk. 



Lime S3 



Carbonic acid 42 



Silex and alumine .... 2 



Water .••.•#.. 3 



100 Kirwan. 



In concluding, I find that Mr. Pkiyfair, who ranks so high in the 

 annals of science, has alluded to the black veins which traverse the 

 white granular marble of Carrara having a resemblance to the sutures 

 in the human scull: — are those very remarkable fissures confined alone 

 to the calcareous strata ? 



It appears that Herm granite is effectually crushed by a pressure of 

 6"G4 tons on the superficial inch; and that a cube of it containing G4 

 inches weighed Gibs. G oz., consequently a cubic foot weighs 172"125 

 lbs., and that there is 13"U13 cubic feet to the ton; then it takes 6*G4 

 tons, or SG-il cubic feet of its own mass to crush one superficial inch, 

 consequently a column an inch square of Herm granite containing SG'41 

 cubic feet would reach to an elevation of 12,443 feet, or 2 miles and 

 G28 yards high, or 3G times higher than St. Paul's Steeple,* before it 

 would reach its maximum elevation of crushing by its own weight at 

 the base. 



Craigleith stone is crushed by about 3 tons weight on the superficial 

 inch, — 137-V cubic inches weighed 11 lbs. lUoz., a cubic foot than 

 14G-094 lbs., being 15-34 cubic feet to the ton, or 4G-02 cubic feet of 

 its own mass to crush a superficial inch. A column of Craigleith stone 

 containing 4G'U2 cubic feet and one inch square would crush at its base 

 by its own weight at the height of GG24 feet, or one mile and 448 

 yards, being more than 19 times the height of St. Paul's steeple. 



A four sided pyramid of Herm granite whose side at the base would 

 be one inch and containing 8G"41 cubic feet, would reach an elevation 

 of 37,329 feet, or 7 miles and 123 yards before it would be crushed by 

 its own weight at the base, equal to 1U9 times the height of St. Paul's 

 steeple. 



And a four sided pyramid of Craigleith stone whose side at the 

 base would be one inch, and containing 4G'02 cubic feet, would reach 

 an elevation of 19,S72 feet, or 3 miles and 1344 yards, before it would 

 be crushed bv its own weight at the base, equal to more than 5S times 

 the height of St. Paul's. 



PUBLIC BUILDINGS IN LONDON, 



A Critical Review of the Public Buildings, Statues and Ornaments in 

 and about London and JVestminster — 1734. 



By R.vlph. 



[In consequence of this pamphlet being out of print and very scarce, 

 we have deemed it advisable to rejnint such portions as relate to 

 those buildings that still remain undisturbed. Ever since its first 

 appearance, it has always been read by the architect with considerable 

 interest. It was printed anonymously, but it was well known to be by 

 an eminent critic of the .day, Ralph, the progenitor of Ralph Redi- 

 vivus, whose eft'usions have occupied several numbers of our Journal, 

 and created considerable interest in many of our architectural readers ; 

 but since the latter has deserted us, we hope only for a short period, 

 we shall occupy oooasionally our pages with some extracts from the 

 above work.] 



As nothing contributes more to the grandeur and magnificence of a 

 city, than noble and elegant buildings, so nothing produces a heavier 

 censure on a nation's taste than those which arc otherwise ; it is for 

 this reason highly laudable to stir up the public to an attention, to such 

 elegant and proper decorations as these, not only in regard to the 

 fame of the people in general, but their interest too. One of the 

 chief re.isons why Italy is so generally visited by all foreigners of 

 genius and distinction, is owing to the magnificence of their structures, 

 and their number and variety ; they are a continual bait to invite 

 their neighbours to lay out their money amongst them, and one may 

 reasonably assert, that the sums which have been expended for the 

 bare sight of those elegant piles, have more than paid the original 

 charge of their building. "Tliis Louis XIV. was sufficiently apprized 

 of when he undertook Versailles, and the company that single fabric 

 only has drawn into France, has made that crown ample amends for 

 the expence of erecting it; and they have both the use and reputation 

 of it still into the bargain. 



It is high time, therefore, for us to look about us too, and endeavour 

 to vie with our neighbours in politeness, as well as power and empire. 

 Towards the end of King James I.'s reign, and in the beginning of his 

 son's, taste made a bold step from Italy to England at once, and scarce 

 staid a moment to visit France by the way. From the most profound 

 ignorance in architecture, the most consummate night of knowledge, 

 Inigo Jones started up a prodigy of art, and vied even with his master 

 Palladio himself. From so glorious an out-set, there was not any ex- 

 cellency that we might not have hoped to obtain , Britain had a rea- 



* lakiBs the steeple at 340 feet, 



