GLASS AND GLAZING. 



537 



Corroboranted glass. — This glass was 

 brought into notice a few years ago by- 

 Mr Apsley Pellatt, who describes it to be 

 both stronger and better calculated to 

 prevent the drip by reason of the rain 

 entering between the laps, and, at the 

 same time, lessen, if not wholly remedy, 

 the formation of globules from condensed 

 steam on the under side of the roof, 

 which is known to form lenses, and to 

 cause serious injury to the leaves of the 

 plants. This glass is of an arched form, 

 7 inches broad and 20 inches long. A 

 roof glazed with this arched or cor- 

 roboranted glass would have a very 

 novel appearance, somewhat resembling 

 a roof of corrugated iron. This glass 

 being of moderate and uniform thick- 

 ness, and being periscopic, has no ten- 

 dency to burn the plants placed under 

 it, nor to reject the sun's rays at any 

 angle of impingement. A roof glazed 

 with it to a certain extent becomes a 

 modification of a ridge-and-furrow one. 

 This form of glass requires the sashes 

 to be made expressly on purpose, at 

 least the astragals must be of a different 

 form from those in ordinary use. 



Polished thick plate glass, we appre- 

 hend, will be found inapplicable to the 

 roofs, at least of horticultural erections, 

 for reasons apart from the enormous ex- 

 pense. It is an established law that light 

 is transmitted through glass in exact 

 proportion to the angle at which it falls 

 on the surface. At 45° it is found that 

 exactly half the light passes through, and 

 the other half is reflected off at the same 

 angle into the air. We apprehend that 

 heat follows the same law ; and when we 

 come to very acute angles, total reflection 

 takes place, and this occurs with thick 

 glass at a larger angle than it does with 

 the glass commonly used. 



Russell's patent glass tile. — The follow- 

 ing description and illustration will ex- 

 plain this invention. About half an inch 

 of the opposite sides of a flat sheet of 

 glass, of any dimension that may be de- 

 sired, are bent upwards until they form 

 a flange nearly at right angles to the 

 plane of the glass, and about half an 

 inch deep of the section. The ends are 

 made of unequal breadths between the 

 flanges, so that the narrow end of one 

 tile may go easily within the flanges of 

 the broad end of another, as shown in 



VOL. I. 



fig. 758. The tiles are placed in rows 

 along the roof, the narrow 

 lg ' ' end downwards, the wide end 

 upwards, resting on a purlin 

 of small dimensions, between 

 the principal rafters : the 

 lower ends of the second row 



i of tiles are placed within and 



above the upper and wide 

 ends of the first row, with a 

 lap of half an inch : the ad- 

 jacent flanges of each pair 

 of tiles, which are from a 

 quarter to half an inch apart, 

 are then covered with a metal hollow 

 bead, screwed down at one end to the 

 purlin below, the crown of the bead being 

 filled with putty before it is put on. 



The saving effected in the first con- 

 struction of the roofs of hothouses or 

 conservatories, by using this tile in place 

 of the usual sashes, is from 10 to 15 per 

 cent, taking glass of similar strength in 

 both cases. The sashes, as in ordinary 

 construction, are entirely dispensed with, 

 and the rafters need not be placed nearer 

 each other than 6 feet, rendering the 

 roof more open and light. 



The purlin or small cross-rafter, upon 

 which the ends of the tiles rest, affords 

 an excellent means of catching the mois- 

 ture, condensed upon the inner surface 

 of the glass, into a rone or groove cut out 

 of the upper side of the rafter, and lined 

 with thin marine metal, and which falls 

 into a pipe trained down one of the 

 rafters. Dripping of moisture from the 

 roof is thus prevented. 



Keeping out of view the saving effected 

 in the first cost of roofs for horticul- 

 tural purposes by using these tiles, the 

 following very desirable objects are at- 

 tained : — 



First, No timber on the roof, with the 

 exception of part of the cope of the ridge 

 beam, is exposed to the weather. 



Second, No putty is exposed : the putty 

 used is covered by the metal bead. 



Third, No paint is required, and 

 consequently the continually recurring 

 repairs or renewal which putty and 

 paint need every second or third year 

 are altogether avoided. 



Fourth, The roof is nearly air-tight, 

 and must therefore render the heating 

 more effective, and consequently econo- 

 mical, as no part of it is wasted by escape. 



3 Y 



