CHAPTER X. 



DETAILS OF CONSTRUCTION. 



§ 1. — GLASS AND GLAZING. 



Until the repeal of the duty on glass we 

 had few varieties, and, if we except crown 

 glass, still fewer fit for horticultural pur- 

 poses. Now we have many, of which the 

 following may be considered the best, — 

 viz., British plate, patent plate, rough 

 plate, patent rolled rough plate, crown in 

 various qualities, British sheet, Belgian 

 sheet, &c. &c. 



In regard to the respective merits of 

 these glasses, opinions are still as much at 

 variance as they have long been ; and 

 they are likely so to continue. Crown, 

 British sheet, and Hartley's patent rough 

 plate are amongst the principal now in 

 use. Inferior sorts of crown and sheet 

 glass are manufactured, and find their 

 way into the market under the denomi- 

 nation of cheap horticultural glass. As 

 an instance of this we may state, that 

 there are no less than five qualities of 

 ordinary crown glass, varying in price 

 from £2, 6s. to £6, 15s. per crate of 

 eighteen tables ; and in the case of sheet 

 glass, 1 6 oz. to the foot, even when taken 

 in crates, the difference in price is from 

 Is. to 3Jd. per foot ; of 21 oz., from Is. 3d. 

 to 5d. ; of 26 oz., from Is. 6d. to 6Jd. ; 

 and of 32 oz., from Is. 9d. to 9d. per 

 superficial foot. We presume the quality 

 in each class differs in a like proportion. 

 This requires to be guarded against. 

 Opinions regarding the merits of British 

 sheet, and other modern improved kinds, 

 have been, and still are, very conflicting. 

 Notwithstanding all their presumed evils 

 we would be sorry to lose them, both on 

 account of their elegance in appearance 

 and their economy in use. There can be 

 little doubt that insufficient ventilation 



is the principal cause of the accidents 

 that have arisen from the use of these 

 when of a large size ; for we believe the 

 same effects have occurred in glass of all 

 descriptions when used beyond the old 

 dimensions ; and this opinion is confirmed 

 by the circumstance, that where they have 

 been used of small dimensions, the scorch- 

 ing and burning complained of have been 

 scarcely recognisable — at least to a greater 

 degree than in the glass formerly used. 

 The best quality of crown or sheet glass 

 will produce disastrous effects where ven- 

 tilation is neglected ; and of course this 

 will be more evident when glass of infe- 

 rior quality is used — arising chiefly from 

 unequal thickness, undulated surface, and 

 specks and nebules existing in it. These 

 defects are daily disappearing as the 

 manufacture is improved — the more so 

 as cultivators are now aware of the neces- 

 sity of a more abundant ventilation. It 

 should be borne in mind, that for a hot- 

 house roof, glazed with glass of whatever 

 quality, in pieces 1 foot in breadth, and 

 possibly 3 or 4 feet in length — more 

 especially if the laps be cross-puttied — 

 a much greater amount of artificial venti- 

 lation will be required, than in the case of 

 another roof glazed with the same quality 

 of glass 6 inches by 4 inches ; — as in the lat- 

 ter, however thoroughly it may be kept in 

 repair, air is admitted through the laps to 

 an extent greater than is generally sup- 

 posed. The same cause produces another 

 effect, namely, condensation — and this 

 often to excess — from the same amount of 

 evaporation from within. In roofs glazed 

 with small glass, and with innumerable 

 laps, this condensation is allowed to 

 escape to the exterior surface ; whereas, 

 in the case of large panes being used, the 



