50 



GLAZING. 



perfect; for if they be injured, it is difficult to repair them without 

 taking them out of the brick work, which is attended with considerable 

 expense, and cannot be done when the fires are in constant use." 



GLAZING. 



Glazing is a veiy important matter in hot house building. The glass 

 should be cut so as to fit the rabbet exactly, but not too tight ; it should 

 be cut upon the curvihnear principle, and well bedded, not only in the 

 rabbet, but also in the overlaps, which latter should not be broader than 

 one eighth of an inch, and laid in coloured putty, that of a black colour 

 has the best effect. It is the utmost extravagance to talk of plate glass 

 only being used for greenhouses. Some theorists also assert, that 

 puttying the laps darkens the house and excludes the sun's rays. No 

 doubt this is to some extent true ; but were they left open when first 

 finished, many weeks would not elapse before that they would become 

 filled with dust and filth, which would exclude the same proportion of 

 light, and instead of excluding the water, would rather tend to attract it 

 into the house. The gi'eat advantage of puttying the laps is to prevent 

 the breakage of glass, by leaving room for expansion in time of frost, and 

 also by the glass having three soHd bases to rest upon instead of two. 



If economy be an object of consideration, the glass used may be cut 

 under the size subject to duty, which will make a considerable difference 

 in the expense, and will in all ordinary cases answer every useful purpose. 

 In using the smaller sized glass, the laps may be left unputtj-ed, but their 

 breadth should not exceed the eighth of an inch, which will carry off 

 the water better than a lap of an inch and a half in breadth. 



Green glass was formerly used in this country for hot house roofe, and 

 such is generally used to this day on the Continent, but it is of all sorts the 

 worst ; for if, as Bouguer has shewn, one fortieth part of the hght which 

 falls perpendicularly on the purest crystal is reflected off, or does not 

 pass through it, it may safely be asserted that green glass reflects off more 

 than three fourths. Economy, as to the quahty of glass, therefore, is 

 defeating the intention of bmlding hot houses, which is to imitate a 

 a natural chmate in all the qualities of light, heat, air, water, and earth, 

 as perfectly as possible. The best crown glass only should be used, and, 

 as we have already stated, it should be cut upon the curvihnear prin- 

 ciple, and bedded and fastened in with soft putty, formed of well wrought 

 paste of flower, mixed -svith whitening and raw Unseed oil, which is 

 most durable, but requires a much longer time to dry. The hard sorts 



