542 



DETAILS OF CONSTRUCTION. 



noticed in connection with his glass walls, 

 vide page 91, and fig. 80. By subsequent 

 information received from the intelligent 

 inventor, we find that strips of india- 

 rubber are placed on top of the sash-bars 

 for the glass to lie upon, as well as over 

 it, on which the beading rests. Se- 

 curing the glass in all hothouse roofs 

 by means of portable beading, as here re- 

 commended, will shortly, we have no 

 doubt, become the general practice in all 

 new erections, because it has reason in its 

 favour ; the only difficulty at present 

 being in the construction of the screws, 

 which are apt to become difficult of ex- 

 traction. This, however, could be reme- 

 died by forging their heads like square 

 nuts, sufficiently thick to admit of a turn- 

 screw wrench, instead of a screw-driver 

 being applied. Another improvement 

 would be making the beading of glass, 

 instead of wood or metal. By this means 

 we would have the entire surface composed 

 of two imperishable materials, viz., glass 

 and copper. In the manufacture of glass 

 beading there would be no difficulty in 

 forming perforations for the screws at 12 

 inches apart. The greatest improvement 

 that can take place in glazing is the total 

 disuse of putty and paint, which such a 

 mode as this would completely realise. 



Jeffrey's marine glue has been recom- 

 mended as a substitute for putty, and 

 when laid on the astragal to the thickness 

 of a quarter of an inch, and over the glass 

 about 3-eighths of an inch, has been found 

 to stand both frost and heat. Its elasti- 

 city prevents the breaking of the glass 

 when the sash is shaken or carelessly let 

 fall, which is no slight recommendation to 

 its adoption. It is more expensive than 

 common putty ; but as it is almost impe- 

 rishable, and requires no paint, this is a 

 matter of less consequence. It should be 

 thoroughly melted in a common glue-pot, 

 using oil instead of water in the outer 

 vessel, and applied quickly by using an 

 iron spoon. Any of the glue that runs 

 over the glass maybe easily removed with 

 a knife or chisel. 



One of the principal causes of the 

 breakage of glass is too tight glazing, 

 more especially in metallic roofs, when 

 expansion and contraction are going on 

 upon all sudden changes of the tempera- 

 ture, and the evil practice adopted by 

 some tradesmen of sprigging down — that 



is, putting small sprig nails into the astra- 

 gals of wooden roofs, at the corners of the 

 panes, when they happen to be a little 

 crooked or of uneven surface ; for on a 

 sudden blow being given to the sash, the 

 glass is sure to crack, beginning at the 

 point where it comes in contact with the 

 resistance of the sprigs. But the greatest 

 of all causes of breakage is open over- 

 laps, and this is increased in proportion 

 to their breadth. The water that finds 

 its way between the laps, whether from 

 capillary attraction, the dashing of rain 

 against the roof, or otherwise, becomes 

 frozen unless the temperature within be 

 kept sufficiently high to prevent it ; and 

 as water, when converted into ice, be- 

 comes much enlarged in volume, the 

 breakage of the glass by expansion natu- 

 rally follows. All roofs should be cross 

 puttied — that is, the overlaps filled in with 

 some material that will exclude water, if 

 the preservation of the glass be a consi- 

 deration. The lap need not be more than 

 one quarter of an inch in breadth, even 

 where the panes are large ; and where 

 they are small, (say 6 inches by 4,) one- 

 eighth of an inch is quite sufficient. 



The best system of glazing sashes 

 of the ordinary construction, in our 

 opinion, is to cut the lower ends of the 

 panes on the curvilinear principle ; — to 

 bed them evenly on a putty bed ; bring the 

 two surfaces as close together as possible 

 at the overlaps, and, keeping these about 

 two-eighths of an inch in breadth, putty- 

 ing them, or introducing a copper or lead 

 lap between them— leaving, however, al- 

 ways an open space in the centre of the 

 lap, of about a quarter of an inch, to allow 

 the condensed steam from within a free 

 passage to the outer side of the roof ; — to 

 draw the paint-brush along the sides of 

 the squares to the breadth of the shoulder 

 of the rebate, and, when this is dry, to 

 put on the fore putty ; — then, when suffi- 

 ciently dry and quite hard, but not till 

 then, give the whole three coats of white- 

 lead colour reduced to a stone shade. 



A very great deal of the durability 

 of glazing depends on old putty of the 

 best quality being used, and that it gets 

 perfectly dry before painting. It is need- 

 less to observe that the sashes should be 

 quite dry before the glazing commences, 

 and that they should be primed and knot- 

 ted also. In repairing glass roofs, which 



