153 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[May, 



tlie want of a necessary proportion of oxygen in the mixture, — which the 

 following experienci' will go far tu prove. 



The tint of green is always minus when the lead in the glass mixture is in 

 the highest state of oxygenation — that is, when red-lead is used; and lowest 

 when litharge is employed in the mixture. When an excess of earhonate of 

 jjotash is used, the green tint is deep, hut may be entirely overcome hy the 

 use of the nitrate of potash, and superseded hy a purple tint when no metal 

 but lead is present. 



Oxygen being the agent by which these changes in the colour of the glass 

 are effected, the glassmaker, in order to overcome the green tint always 

 present when oxygen is minus, uses the oxide of manganese, which has the 

 property of giving off its oxygen very slowly. An excess of manganese 

 gives to glass a purple tint, and where altogether absent the glass is always 

 green. 



Having thus called attention to the peculiar composition and mode of 

 manufacturing flint glass, he proceeded to describe the changes which take 

 place in the colour or tint of glass, and the methods employed by the glass 

 manufacturer to convert the mass from a green, purple, amber, or other tint, 

 to a pure or colourless metal ; and brought forward examples tending to 

 jirove that the changes in the colour of glass are due to the presence or 

 absence of a given proportion of oxygen. Manganese, as a metal, gives no 

 colour to glass, although hy the oxygen it yields to the lead in the mixture 

 a purple colour is produced, because by reducing the quantity of oxygen, 

 either by polling or subjecting the glass to a long continued heat, or by sub- 

 iiiitting it to the action of carbon, the purple colour is removed, though the 

 manganese still remains. Iron and copper also assume different colours 

 ■when combined with different proportions of oxygen. If this be true, may 

 not all colours of the oxygen of other metals, such as iron, copper, and lead, 

 be due to the combination of certain proportions of oxygen with the metal 

 or metals present, so as to induce a particular molecular arrangement, from 

 which the glass has the power of absorbing a particular colour ? 



A lengthened discussion followed the reading of the paper, in which 

 Mr. A. Pellatt, Mr. Christie, Mr. Wilson, Mr. Palmer, and other gentlemen 

 connected with the manufacture, took part, at the close of which the thanks 

 of the meeting were presented to Mr. F. Pellatt for bis commuuication. 



ROYAL INSTITUTE OF BRITISH ARCHITECTS. 



March 19. — Ambrose Poyn',t3B, Esq., V.P., in the Chair. 



A letter was read from Mr. B. Ferrey, containing a sketch of the life of 

 the late Mr. Miles, an associate of the Institute, who died recently at the 

 early age of thirty-two yenrs. 



Mr. Geoghegan exhibited a rubbing from the frieze of an Elizabethan 

 mantelpiece, discovered lately during the alterations to Wiarton House, near 

 Staplehurst, Kent. In the original, which is elegantly executed in the Kent- 

 ish rag-stone, the pattern is very slightly incised in the stone. 



Mr. Std.n'ey Smirke, V.P., read 8 paper "On the contents of a work by 

 Sir Balthazar Gerbier, written in the 17th century, and entitled 'Comiset and 

 Advice tu all Builders,' together with some remarks suggested thereby." (See 

 Journal, p. 153.) 



Tlie Chairman observed that, although Gerbier's work was undoubtedly 

 one of the earliest on the suhjett in our language, it was not the first. Wal- 

 pule mentions a treatise hy John Shute, a copy of which had recently been 

 recovered hy Professor Willis. 



Mr. Taylor, jun., described his patent method of facing walls with stone. 

 It was mentioned, in connection with the subject, that the tower of Chelsea 

 new church was faced after the brickwork of it was finished, and that the 

 masons began at the top and worked downwards. Projecting courses bad 

 lieen worked in.* 



y^jirit 10. — Sydney Smirke, Esq., V.P., in the Chair. 



The Chairman announced that the Royal Gold Medal of the Institute for 

 the year 1848 was awarded to the Signor Cavaliere Canina, of Rome, as 

 the Historian of Architecture from the earliest period, and for bis antiquarian 

 researches,- — he having published a series of important works on the various 

 ttyles of art, and likewise on the Tombs of Etruria, the cities of Latium, 

 and other antique remains. 



The Report of the Council relative to the competition for the "Soane 

 Medallion" and the "Medal of the Institute," was read and adopted; when 

 the author of the successful Essay on Palladian Art was announced tu be 

 Mr. Wyatt Papwortii. 



A paper was read "On the Hollow Brick Ceiling recently turned over 

 St. George's Hall, Liverpool." By Robert Rawlinson, Esq. 



Having stated that it had been the intention of the late Mr. Harvey L. 

 Elnies, the architect of this building, to construct the ceiling with patent 

 compressed bricks, Mr. Rawlinson observed that he in using the hollow 

 bricks bad only adopted a mode of construction known to the ancients, and 

 also applied to some of the early Christian churches in Italy — and in build- 

 ings of a more recent date. He stated that, although not much in use of 

 late years, these hollow bricks are now likely to be more generally applied; 

 as, owing to a relaxation of the excise laws and the application of m.ichinery, 



* Facing the brickwork with sloue after the liqilding is erected is not Dew: it was 

 jiflnpled by Sir Robert Sniiriie, in the Temple, to the new Chanib^rs, and ulBO at the 

 1. litisU iMuaeum.— i-.d. C'.E. ft; A. Jou.nal. 



they can be manufactured at a less cost than solid bricks — while they pos- 

 sess the advantage of being lighter. It has been suggested, too, that tlie 

 hollow bricks may be econdmically applied in the construction of the parti- 

 tion and external walls of cottages and other buildings, with the advantage 

 of combining dryness with facility of ventilation. 



The construction of the arch in question was of some importance from its 

 size, the span being sixty-eight feet and its thickness one foot. The hrii ks 

 used by Mr. Rawlinson were twelve inches in length and four inches square, 

 with a longitudinal perforation two inches in diameter. The weight and 

 cost of the arch thus constructed was one-fourth less than they would have 

 been had solid bricks been used. The work was set in mortar (formed of 

 Halkin lime used fresh and made in a steam-mill), with the exception of five 

 feet on each side of the key, which is set in cement. The spandril walls are 

 similarly constructed, at distances of four feet six inches, with circular open, 

 ings which afford a passage along the sides. On removing the centerings, 

 the arch was found to have deflected only three-eighths of an inch. 



ROYAL SCOTTISH SOCIETY OF ARTS. 

 March 12. — George Lees, Esq., A.M., V.P., in the Chair. 



The following communications were made: — 



" On the Warming and Ventilation of Dwelling Houses." By Captai.v 

 John H. Hall. 



A communication on the economical warming and ventilation of dwelling- 

 houses by means independent of open fires in the several rooms — consisting, 

 first, of general observations on the inefficiencv and wasteful character of 

 the existing method of warming houses ; and, secondly, describing cer- 

 tain arrangements for insuring an uninterrupted supply of warmed fresh air 

 to any one or more, at pleasure, of the several apartments of a house, by the 

 use of one stove or warming apparatus. 



"Description of a Tubular Raihray Bridge of a new construction.^* By 

 Daniel .Miller, Esq., C.E. 



In this design it is intended to form a construction of malleable and cast 

 iron, so as to apply their respective properties in the most advantageous 

 manner to resist the opposing strains of tension and compression which are 

 brought into action in a structure of this nature. A drawing shown repre- 

 sented a design on this principle for a railway bridge to cross the Clyde at 

 Glasgow Harbour in two spans of 200 feet each. Each span consists of three 

 girders, each 18 feet deep, which divide the bridge into two lines of rails. The 

 upper part of each girder is formed of a circular tube of cast-iron, 2 ft. 9 in. 

 diameter, which is of the best form and material for resisting compression. 

 The upper side of the tube is thicker than the lower, as the inner circumfer- 

 ence is eccentric to the outer. The lower part of the girder consists of a 

 rectangular tube, 3 feet deep by 2 ft. 9 in. broad, formed of plates of mal- 

 leable iron chain, rivetted and strengthened at the corners by angle-iron. 

 This is considered the best form for resisting the tensile strain and preserving 

 the necessary rigidity. These two tubes, forming the upper and lower sides 

 of the girder, are united by frames of toughened cast-iron, which are cast of 

 an open trussed form, so as to secure lightness and strength. At intervals of 

 15 feet, brackets are attached on each side of the centre of these frames, 

 from the extreiuities of which proceed wrougbt-iron rods to the top and 

 bottom, for the purpose of increasing the lateral strength and rigidity of the 

 frames. The girders are united to each other transversely, both at top and 

 bottom, by an arrangement of braces and struts of wrought and cast iron. 

 All the cast-iron in the structure is proposed to be of Mr. Stirling's tough- 

 ened cast-iron, which, by the recent government experiments, is proved to 

 possess remarkable advantages in elastic resistance, and in resisting compres- 

 sion and tension; and removes the objection hitherto prevailing again^t 

 employing cast-iron for railway bridges of large span, or where exposed to 

 vibratory action. 



The author considers that this combination of malleable and toughened 

 cast-iron will fulfil the principal conilitions required in such a structure, iu 

 economy, rigidity, elastic resistance, and ornamental appearance. 



" On a new Electro-Magnetic Coil-Machine." Bv Dr. Thomas Wright, 

 F.K.C.P. 



Dr. Wright stated that his machine consists of a bundle of thin iron wires, 

 seven inches long by six-tenths of an inch in diameter, wound with thirty 

 yards of No. 16 copper wire. It is fixed by half its length in a frame of 

 wood, the other half being free, to permit a thick brass tube to slide over it. 

 It is furnished with a self-acting adjustment for interrupting contact wiih 

 the battery, an account of which was published by the author in Sturgeon's 

 "Annals of Electricity" for March 1840, and which is, the author believes, 

 used in all electro-magnetic coil-machines. The great power of this instru- 

 ment was stated to depend upon the accuracy of the construction of the 

 electro-magnet. A great number of experiments were instituted by Dr. 

 Wright, for the purpose of determining the proportion to he observed be- 

 tween the coil wire, the iron to be magnetised, and the battery; this differs 

 with the kind of battery used, but for general purposes the arrangement 

 above described appears to be the best. Dr. Wright stated that it is most 

 essential that the coil wire be brought as close as possible to the iron ; and 

 that to effect this, the coil wire is simply insulated by a single layer of the 

 thinnest tissue paper, instead of the coverings of worsted or cotton which 

 are generally used. Dr. Wright stated that an instrument thus constructed. 



