2i8 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[June, 



" Description of the Antiquities of Deles,"' -gave a representation of a portal 

 or gateway on the ascent of ilount Cynthus, formed to support the wall of 

 the ancient fortifications. The entrance was constructed with ten large 

 stones inclined to each other, like those at the aperture into the great Egyp- 

 tian pyramid. It was perhaps the earliest specimen of Pelasgic architecture 

 in Greece, displaying the first step towards the principle of the arch. That 

 it was known hy the Etruscans seeuied evident, from the remains of arches 

 and hridges, now existing in the country of the Volsci in Italy ; and the re- 

 searches of travellers in that country, within the last few years, had brought 

 to light many curious examples, anterior to the period of the Cloaca; of 

 Rome, and the tunnel of Albano by Ancus Martius. Mr. Rennie was of 

 opinion, from his examination of the subject, that there existed no sufficient 

 evidence, to establish the knowledge, or use of the arch among the Greeks. 



Mr. Page presented two sketches made by him of two arches at Cape Crio 

 (Cnidus, Rhodes). These arches were semicircular, built of large stones re- 

 gularly radiating from a centre, without any mortar in the joints, and stood 

 among Cyclopaean remains, of which they apparently formed a part. He 

 was of opinion, that the Greeks were aware of the properties of the arch. 

 They evidently appreciated its form, for it must have been noticed by all 

 travellers, how frequently the flat lintels were cut out on the under side ; 

 several specimens of this existed in the sepulchral remains now in the British 

 Museum. At Athens, he had noticed a very considerable excavation of a 

 regular arched form through solid marble. 



Mr. Rennie obseived, that as more useful lessons were given by failures in 

 construction, than by records of successful undertakings, he had caused a 

 large drawing to be made, of the bridge of Boverie at Liege, showing its 

 state at the time of the report upon it, by the commissioners appointed by 

 the Belgian Government, when it was condemned, and was ordered to be 

 reconstructed, at the cost of the contractor, which however had not yet been 

 done. The bridge, which was built of hard, compact, niagnesian limestone, 

 consisted of five arches of 78 feet span each, with a versed sine of 8 feet, 

 which was between ith and ^oth of the span. The form of the arch was 

 that of a segment of a circle of 100 feet radius, the angle of the springing 

 was therefore 46° 45'. The abutments at either extremity were of rubble 

 masonry, and were very deficient in weight and dimensions. The obvious con- 

 sequnce of this want of due proportion was, that the abutments gave way, all 

 the arches sunk at their centres, many of the stones nearly falling out, several 

 of them were fractured in both directions, serious dislocations occurred in each 

 pier, above the springings of the arches, and also down upon the cutwaters, 

 and in spite of all attempts to remedy the defects, the bridge was condemned 

 and was taken down, although it had cost upwards of £25,000. It was evi- 

 dent that these flat arches were not well proportioned, and that the abut- 

 ments were insufficient to support their thrust. It appeared also, from the 

 report of the Commission (of which he presented an abstract, No. 672), that 

 sufficient attention had not been paid to the quality of the workmanship, or 

 in the selection of the materials employed. 



ROYAL INSTITUTE OF BRITISH ARCHITECTS. 



June 3. — T. B. Papworth, V.P., in the Chair. — Mr. C. II. Smith resumed 

 the subject commenced on the 29th April, (see Journal, p. 200), " On the 

 Magnesinn Limestones, especially u-itk reference to those employed in the New 

 [ Houses of Parliament." — Previously to the Commission appointed to investi- 



U gate the choice of a material for the Houses of Parliament, the proper selec- 

 tion of stone for building purposes with regard to its quality had been strangely 

 neglected. Public attention was first called to this subject by Sir H. De la 

 I Beche in 1835, and the inquiries, originated by that gentleman, resulted in 



'! tlie establishment of the Museum of Economic Geology and the Commission, 



of which Mr. Smith was a member. On the first preparations for rebuilding 

 the Houses of Parliament, efforts were made by our neighbours in Normandy 

 for the introduction of Caen stone, and a great number of specimens were 

 sent, comprising stone of every quality, from the best to the worst, all pass- 

 ing under the same name. In selecting the stone for the Houses of Parlia- 

 ment, the Commissioners had to take into consideration a variety of circum- 

 stances, independent of the mere quality ; as the situation of the quarries, 

 the facility of water-carriage, and the assurance that the supply of stone 

 would not fail during the progress of the work, and that the cost of labour 

 upon it should not greatly differ from that upon the building stones in gene- 

 ral use. Upon comparing the produce of many quarries, the Bolsover Moor 

 stone appeared to the Commission to be the best adapted ; and as beds of 

 stone of nearly the same quality extend over a tract of about fifteen miles 

 from nortli to south, the quarries of North Anston were finally selected, as 

 uniting in the greatest degree all the conditions demanded. In this locality 

 an ample supply of stone lies at a depth of from ten to fifteen feet. Eight 

 beds of stone of the best quality, are found lying nearly level, the uppermost 

 affording blocks of four feet thick, and the remainder from two feet and a 

 half to eighteen inches. The quantity of stone supplied from the Norfol 

 Quarry at North Anston, between February 1840 and April 1844, amounted 

 to 726,893 cubic feet. Mr. Smith made some remarks on the effect of lichen 

 on the surface of stone, which has been supposed favourable to its preserva- 

 tion. His own observation had led him to a different conclusion, as he had 



12 •' Antiquities of Atli«ns,"&c, Stewart and Kevett, Supplement. Folio, Lon- 

 don, 1830. 



found stone covered with lichen reduced to powder to the depth of a six- 

 teenth of an inch on its removal ; and he suggested that the lichen had had 

 the effect of absorbing some of the elements of the stone. In some speci- 

 mens of magnesian limestone the lichen appeared to have taken up the lime 

 and left the magnesian. 



June 7. — Right Hon. StukGes Bourne, V.P. in the Chair, Mr. Faraday 

 " On recent Improvements in the Manufacture and Silvering of Mirrors,'^ — 

 Mr. Faraday's subjects were : 1 . The manufacture of plate-glass. 2. The 

 ordinary mode of silvering mirrors. 3. The new method of producing this 

 result, lately invented and patented by Mr. Drayton. — 1. Mirrors are made 

 with plate glass. Mr. Faraday described glass generally as being essentially 

 a combination of silica with an alkaline oxide. The combination, however, 

 presents the character of a solution rather than of a definite chemical com- 

 pound, only it is difficult to affirm whether it is the silica or the oxide which 

 is the solvent or the body dissolved. From this mutual condition of the in- 

 gredients, it follows that their product is held together by very feeble affini- 

 ties, and hence, as was afterwards shown, chemical reagents will act upon 

 these ingredients with a power which they would not have were glass a de- 

 finite compound. Mr. Faraday noticed, that as glass is not the result of de- 

 finite proportionals, there are many combinations of materials capable of 

 producing a more or less perfect result. Each manufacturer, therefore, has 

 his own recipe and process, which he considers the most valuable secret of 

 his trade. It is, however, well known, that the flint-glass maker uses the 

 oxides 'of lead and of sodium, the bottle-glass maker lime, (an oxide of cal- 

 cium) and the plate-glass maker, in addition to soda, has recourse to arsenic. 

 Mr. Faraday then adverted to the corrosions which take place in tlie inferior 

 qualities of glass, owing to the feeble affinity with which tlieir ingredients are 

 held together. He stated, that from the surface of flint glass a very thin film 

 of soluble alkali was washed off' by tlie first contact of liquid, leaving a fine 

 lamina of silica, the hard dissoluble quality of which protected the substance 

 which it covered. If, however, this crust of silica chanced to be mechani- 

 cally removed, the whole of the glass became liable to corrosion, as in ancient 

 lachrymatories and other glass vessels. Mr. Faraday illustrated this hy the 

 corroded surfaces of two bottles, one obtained from a cellar in Threadneedle 

 Street, where it had probably remained from the period of the great fire of 

 London, another from the wreck of the Royal George. A still more striking 

 instance of the instability of glass as a compound was exhibited by forma- 

 tions in the interior of a champagne bottle, which had been filled with di- 

 luted sulphuric acid. In this case the acid had separated the silica from the 

 inner surface of the glass, and formed a sulphate with its ingredient, lime. 

 The result was, that the bottle became incrusted internally \»itli cones of 

 silica and sulphate of lime, the bases of which, extending from within out- 

 wards, had perforated the sides of the bottle so as to cause the escape of the 

 liquor it contained. Mr. Faraday referred to the long period of annealing 

 (gradual cooling) whicli glass had to undergo as a necessary consequence of 

 glass wanting the fixity of a definite compound. He concluded this part of 

 his subject by describing the mode of casting plates, and the successive pro- 

 cesses which gradually produce the perfect polish of their surface. 2. Mr. 

 Faraday next exhibited to the audience the mode of silvering glass plates as 

 commonly practised. He bade them observe that a surface of tinfoil was 

 first bathed with mercury, and then flooded with it. That on this tinfoil Ihe 

 plate of glass, having been previously cleansed with extreme care, was so 

 floated as to exclude all dust or dirt ; that this was accompUshed hy the in- 

 tervention of 4 in. of mercury (afterwards pressed out by heavy weights) be- 

 tween the reflecting surface of the amalgam of the mercury and the glass ; 

 and that when the glass and amalgam are closely brought together by the 

 exclusion of the intervening fluid metal, the operation is completed. 3. The 

 great subject of the evening was the invention of Mr. Drayton, which entirely 

 dispenses with the mercury and the tin. (See last month's Journal, p. 206). 

 By that gentleman's process, the mirror is, for the first time, literally speak- 

 ing, silvered, inasmuch as silver is precipitated on it from its nitrate (lunar 

 caustic) in the form of a brilliant lamina. The process is this : on a plate of 

 glass, surrounded with an edge of putty, is poured a solution of nitrate of 

 silver in water and spirit, mixed with ammonia and the oils of cassia and of 

 cloves. 'Fhese oils precipitate the metal in somewhat the same manner as 

 vegetable fibre does in the case of marking ink — the quantity of oil influencing 

 the rapidity "f the precipitation. Mr. Faraday here referred to Dr. Wollas- 

 ton's method of precipitating the phosphate of ammonia and magnesia on 

 the surface of a vessel containing its solution, in order to make intelligible 

 how the deposit of silver was determined on the surface of clean glass, not 

 (as in Dr. W.'s experiment) by mechanical causes, but by a sort of electric 

 affinity. This part of Mr. Faraday's discourse was illustrated by three highly 

 striking adaptations of Mr. Drayton's process. He first silvered a glass plate, 

 the surface of which was cut in a ray-Uke pattern. 2nd. A bottle was filled 

 with Mr. Drayton's transparent solution, which afterwards exhibited a cylin- 

 drical reflecting surface. And 3rd. A large cell, made of two glass plates, 

 was placed erect on the table, and filled with the same clear solution. This, 

 though perfectly translucent in the first instance, gradually became opaque 

 and reflecting ; so that, before Mr. Faraday concluded, those of bis auditors 

 who were placed within view of it, saw tlieir own faces, or that of their near 

 neighbours, gradually substituted for the faces of those who were seated 

 opposite to them. 



The INSTITUTE have resolved to award the following medals next year, 

 to the Authors of the best Essays on the following subjects i — 

 1. On the system and principles pursued by th« Gothic architects from the 



