8J 



NK FOK Uril.DIXi;. 



M'uNK WORKING. 



810 



tonefrakw harden by exposure to the weather ; and it may be observed 

 that thU indurating prooeai take* place the mart rapidly when the 

 water taken up by the sandstones may contain any lime in solution. 



The resistance of building stones to physical force* depends greatly 

 upon the homogeneous nature of their grain, and the direction of their 

 plane* of stratification and cleavage ; the resistance to disintegration 

 and decay depends also very much on the same causes, especially when 

 the stone* are employed in buildings. Thus the stones which have 

 been produced by the deposition of diluvial, or alluvial current*, 

 present distinct traces of bedding, in consequence of the inequalities in 

 the transporting powers of those current) at irt icular periods ; and if 

 those stones should be used in such a manner an to leave the planes of 

 bedding vertical, and parallel to the exposed face of the building, they 

 would be exposed to exfoliation of a very dangerous character. The 

 stones which have been produced by the deposition of substances in 

 suspension in former oceans, such as the oolites, the chalk, ami the 

 freshwater, or marine limestones of the tertiary series, often have 

 planes of bedding produced by the periodic abundance of the animal 

 remains they may contain ; or they may have distinct laminations in 

 consequence tf their mode of crystallisation. In either of these cases the 

 stones would be exposed to crush with greater ease in the direction of 

 the divisional planes, and the effects of the atmosphere would be most 

 energetically exercised when those planes were placed in a direction to 

 favour the absorption of moisture by capillary action, or to allow the 

 stone to exfoliate in a direction parallel to the face. In fact, the most 

 important rule to be observed in the practical use of stone is to place 

 it " in the natural way of the bed," as workmen say ; and though there 

 may be some stones in which it is very difficult to distinguish the bed, 

 and others in which there is less reason than visual for adhering to this 

 law, yet even in them it is preferable to place tho bed of the stones in 

 its natural position. 



A very elaborate report was drawn up in 1839, by a commission 

 named for the purpose of selecting the building-stone to be employed 

 iu the Houses of Parliament ; but in consequence of the marked failure 

 of the material then selected, the recommendations of that report have 

 lately been treated with neglect. This is unfortunate ; because there 

 is much information of value in the report, and the methods of exami- 

 nation it was based upon are substantially correct ; and, as it now 

 appears that the stone actually used in the Houses of Parliament, was 

 not the one recommended by Hie commissioners, the latter ought not to 

 be blamed for the failure which has occurred. The errors which, 

 however, do exist in the report consist in these points : 1. The resis- 

 tances to atmospheric action were appreciated by the state of the stone 

 in certain ancient buildings, which were mostly in the neighbourhood 

 of the quarries from whence those stones had been extracted. 2. In 

 the attempt to judge of the durability of both new and old stones by 

 what is known as Brard's test, or exposing them to the effects of the 

 efflorescence of a solution of the sulphate of soda. Now it is notorious 

 that the atmospheres of large towns contain many elements which do 

 not exist in the atmosphere of the couutry, and nothing but a long 

 exposure to the former would justify an absolute opinion as to its 

 possible effects; even the Caen stone itself resists tolerably well in 

 Lower Normandy, but it decays rapidly at Havre, and more rapidly 

 still in London. The objections raised by the French engineers to 

 Brard's test have already been referred to under ATMOSPHERIC IN- 

 FLUENCE ; and it may suffice here to observe that practically it has 

 been shown to be of very little use as on indication of the durability of 

 a building-stone. 



Before closing these remarks, it may be as well to state that some 

 classes of stones are known by the name of freestone, when they are 

 susceptible of being worked freely by the axe, or by the mallet and 

 chisel ; the ordinary sand and lime stones are of this description, but 

 the granites, whinstoues, slates, and basalts, cannot be worked in this 

 manner. Another technical distinction in the mode of conversion 

 arises from the description of saw used ; the softer stones are cut by 

 the toothed saw, the harder ones are cut by the plate saw and grit. 

 The marbles are susceptible of receiving a polish ; the ordinary sand 

 and limestones remain dull whatever labour may be expended on their 

 faces. The stones which strike fire (or the silicious ones) are usually 

 harder and more durable than the calcareous stones ; but the labour 

 upon them is much more expensive ; and it is almost always the case 

 that tho stones which present ou the surfaces of their fracture, a 

 number of asperities and sparkling focettea aro more difficultly worked 

 than are the stones which present even, dull faces. Of materials of 

 this description the lighter coloured ones are generally softer than the 

 darker ones, and it may be considered a safe rule in judging of new 

 atones, that if they absorb water easily they are not fitted to resist the 

 action of the atmosphere. If the stones should yield a clear ringing 

 sound, they may be considered to be of a fine uniform texture, and 

 free from Hints, earthy nodules, vents, or shakes ; and if in working 

 they should emit a sulphurous smell they would usually prove to be 

 durable. One of the simplest and best precautions to be observed in 

 the use of building-stones, is to quarry them some long time previously 

 to their application, and to expose them to the weather, in order that 

 they may lose gradually what workmen call their " quarry damp." In 

 building*, the denser and harder stone should be used in the lower 

 courses, the lighter ones in the superstructure; the non-absorbent 

 tones should be used in the ground and in plinths, cills, string courses, 



and weather beds of cornices, &c. ; the softer and more absorbent 

 stones may be used for ptiin walling. 



Mr. Hixlgkinson found that the resistance of stone columns to crush- 

 ing weights was nearly uniform when their heights were less than 

 IS times the dimension of their sides; when their heights were 15 

 times their sides, the resistance was manifestly diminished ; ln-n 

 their heights were 24 times their sides, the resistance diminished in 

 the ratio of 188 to 96 nearly ; when they were 30 times the side, ihe 

 resistance became reduced from 138 to 15 ; and when they were 40 

 tunes their side, the resistance was reduced from 138 to 62. Stone 

 columns are considered by Mr. Hodgkinson to yield first at the ends, 

 in consequence of the tendency of rigid bodies to split into wedges, 

 with sharp points at their apices, under the action of superincumln >nt 

 weights. The weight* stone-columns can bear depend at all times on 

 their smallest section. 



Mr. Adie published in the ' Transactions of the British Association 

 for the Advancement of Science,' 1834, some interesting obser. 

 on the expansion of stone under the influence of heat. From these it 

 would appear that within a range of 180 Fahr., the expansion of the 

 Croigleith stone is 0-0011758 of its length, or the same as the expan- 

 sion of glass, and very nearly the same as the ex[>ansion of cast-iron, 

 as ascertained by Lavoisier. The expansion of the black Ualway 

 marble was found to be 0-00043855 of its length ; that of white m:irl>le 

 seems to have been rather less. [HEAT ; RESISTANCE OP MATKKI OS. | 



(Consult Rondelet, VArtde lidtir ; Claudel, Formula d Cns< 

 Inylnieurt; Dumanet, Conn de Construction ; De la Heche's Genl 

 Obtervcr; Report rm Huildlny Stones, 1839; let Annala det Mines, and 

 Its Annala det Fonts ct Chaustfa, passim; let Annala da Ti 

 I'uMiijuts de la Bdyique ; Transaction! of Ae Jiritish Association ; 

 (journal ), passim ; Trantactions of the Society of Arts, 1860.) 



STONKWAKK. [IvuiTiiKNWAHK; POTTKUV AND Poitcr.i.AiN.J 



STONK WORKING. UndtT Ol-AKUY AND QlTAIIHYlMi a i'i. 



tion is given of the mode of detaching and shaping blocks of stone at 

 the quarries. A few lines will suffice to convey an idea of the subse- 

 quent operations. 



Until within a comparatively recent period, few other tools than the 

 saw and chisel were employed in this work ; but now macliiiu ry, 

 moved by steam-power, is extensively adopted. The working of , 

 for ornamental purposes was the chief cause of this change ; seeing 

 that the highly- wrought surfaces might suitably be produced by labour- 

 saving expedients. The sawing by hand of blocks of stone for build- 

 ings, or slabs for pavements, is familiar to every one. The workman 

 employs a kind of blunt knife, which is converted into a species of saw 

 by the presence of sand and water; the action of this blade, by a pro- 

 cess something between cutting and grinding, severs the block of stone 

 into two. The shaping by hand of blocks of stone is equally familiar ; 

 chisels, of various shapes, urged by a mallet, do the whole work. But 

 it is of more elaborate contrivances that we here treat. 



Some of the marble-sawing machines are of the kind shown in the 

 annexed cut. Several saws are fixed parallel iu a frame, at any distance 



Fig. 1. Marble Sawine Machine. 



apart according to the thickness of the slab to be cut. The frame 

 slides in vertical grooves ; and it is so balanced that the saws aiv kept 

 at a height corresponding to the part of the block which is being out. 

 and descend as the cut deepens. These so-called saws atv M 

 soft iron, used with sand and water; the sand being varied in quality 

 according to the kind of stone to be cut. An apparatus is plaivd < .vet- 

 the frame, whereby a little stream of sand and water is made to flow- 

 continuously into each saw-cut. Not only does the use of such a 

 machine save much labour, it saves material also; for in hand sawing 

 the workmen never succeed in keeping the saw in a true plane ; and, 

 as a necessary result, great waste is occasioned in subsequent grinding. 

 Mr. Stewart has recently invented a machine for cutting large mosses 

 of stone ; a series of chisel-cutters follow each other in the same cut, 

 and ore fixed to a frame travelling on a kind of railway. The action of 



