BUILDING MATEKIALS. 



205 



like bars of Portland stone broke at 750 Ibs. ; 

 of Caen stone, at 780 Ibs. The cohesion or 

 tensile strength of a bar, sectional surface 5 

 square inches, weights being suspended from it 

 and increased, was found equal to 1,980 Ibs. ; 

 while Caen stone broke at 768 Ibs., and Port- 

 land at 1,104 Ibs. A cube of 4 inches sustained 

 30 tons pressure before crushing. These stones, 

 however, were all recently made, and time 

 alone can determine the question of their dura- 

 bility. Dr. Frankland found that the finished 

 stone (of course after washing) still contained 

 chloride of sodium, but he judges that this 

 remnant is extractable without injury to the 

 tenacity of the mass ; and although it must ob- 

 viously leave the stone more porous in time 

 than at the first, he considers that this effect 

 will be more than offset by the well-known 

 tendency of the binding material, silicate of 

 lime, to become more crystalline and so harder 

 by age ; so that these artificial stones may yet 

 be found to surpass in durability any natural 

 ones, unless it be the material quarried from 

 the primary rocks. 



Prof. Jas. Thomson read before the British 

 Association a paper on the " Disintegration of 

 Stones exposed in Buildings and otherwise to 

 Atmospheric Influences," in which, setting out 

 with the declaration that he would not be un- 

 derstood as assigning any single cause for the 

 decay of building stones, he endeavored to show 

 the fact of an important mode of such decay, 

 hitherto overlooked. 1. He urges that certain 

 cases of disintegration frequently observed, are 

 not to be referred to the softening or weaken- 

 ing of the stone by dissolving away or chemi- 

 cal alterations of portions of it, but are in- 

 stances in which the crumbling is to be attrib- 

 uted to a disruptive force exerted by certain 

 crystalline matters in the act of solidifying in 

 the pores or cavities of the mass, and from 

 liquids permeating it. 2. That in such cases, 

 the crumbling away of the stones, when not 

 such as is caused by freezing of water in the 

 pores, usually occurs in the greatest degree at 

 places to which, by joint agencies of moisture 

 and evaporation, saline substances existing in 

 the stones are brought and left to crystallize. 

 3. That the solidifying of crystalline matters 

 in porous stones, whether it be of ice from 

 freezing of water, or of crystals of salts from 

 their solutions, usually produces disintegration, 

 not as commonly supposed, by expansion of 

 the total volume of the liquid and the crystals 

 jointly, occasioning a fluid pressure in the 

 pores, but on the contrary, as a consequence 

 of the natural and well known tendency of 

 crystals to increase in size when in contact with 

 a liquid that can still deposit in the solid state 

 the same substance as that composing them 

 this growth in size still going on, even though, 

 to allow of it, the crystals must push out of 

 their way the porous walls of the cavity they 

 are in, and even though it must be from liquids 

 permeating these walls that the crystals receive 

 the materials for their increase. 



A patent has been taken out by Mr. L. Stand- 

 fast, of London, for a composition of burnt 

 clay, iron dust, brick dust, gravel, lime, and 

 sand, mixed with hemp and hair, so as to form 

 a cement, to be laid up in a suitable frame to 

 constitute the walls of houses; such walls 

 when dry being solid, instead of being com- 

 posed of many small blocks. This application 

 of gravel cement for building is similar to the 

 concrete of gravel and mortar already in use for 

 constructing the walls of houses, in some parts 

 of the United States. 



Of a valuable series of papers on ' ; Hydraulic 

 Engineering," bv Mr. Samuel McElroy. C. E., 

 in the (> Jour, of the Franklin Institute," 1862, 

 those in the numbers for May, June, and July, 

 treat of " Reservoir Construction," its history 

 theory, and practice, including the subjects of 

 concretes, masonry, &c. ; those in Nos. for 

 September and October, of " Distribution." In 

 the same journal, March, 1862, will be found 

 an extract from a paper on the " Concrete used 

 in the late Extension of the London Docks," 

 by George Robertson, C. E. The highly spe- 

 cial character of the branch of construction 

 here involved, would render an abstract at 

 length inappropriate in this place. 



The factitious sorts of wood, as those pro- 

 duced by mixing fine saw dust of different nat- 

 ural woods with glue or other cementitious 

 matter, and which are therefore generally ob- 

 tained in a plastic state, and at once compacted 

 and shaped by compressing in moulds, have be- 

 come somewhat familiarly known ; and thus far 

 they have been employed rather for the manu- 

 facture of small articles than for building. 

 Among the best of these is, doubtless, that of 

 M. Ladry, formed by mixing sawdust with bul- 

 lock's blood, and compressing. Another pro- 

 duct of the sort, very recently invented in 

 France, appears to have attracted still more at- 

 tention : it is made of sawdust alone, heated to 

 a high temperature, and in such state subjected 

 to enormous pressure 600 tons, it appears, to 

 the square foot ; and while thus acquiring a 

 compactness and hardness exceeding those of 

 wood, it has a very fine texture, is readily 

 moulded in forming it, and is unchangeable by 

 the atmosphere. It is known as durable wood 

 (bois dure). 



The greatly diminished period of time during 

 which ships are now built being found to re- 

 sult in an injurious increase of the tendency 

 of their timbers to different forms of decay, in 

 consequence of their becoming less thoroughly 

 seasoned on the stocks, M. de Lapparent has 

 within little more than a year past proposed, as 

 a means of preserving the timbers, to carbonize 

 their surfaces to a very slight depth, usually 

 perhaps not exceeding about r T of an inch, 

 by directing upon the surface of the wood a 

 jet of some inflammable gas in the state of ig- 

 nition. A quite uniform carbonization of the 

 surface can thus be secured ; and the resulting 

 coating, it is anticipated, will prove quite im- 

 pervious to air and moisture. The process, the 



