CONSTRUCTION AND HEATING OF GLASS HOUSES. 71 



the surfaces of the metal, and iu the case of galvanized sheet iron 

 destroj's the galvanized surface, and exposes the iron to the rapid 

 and destructive action of rust. 



There are many metal glazing bars in the market, made of zinc 

 and other so-called non-corrosive materials, for which it is claimed 

 that there is sufficient spring to prevent this above-described 

 friction, and while to a certain degree this may be true, in the 

 direction of one bar from another, yet this friction and consequent 

 destruction and displacement is equally as prominent as in some 

 bars without this spring, and in many cases more so, in consequence 

 of the expansion of the bar in the direction of its length. 



Another serious difficulty connected with metal glazing is the 

 great loss of heat in the building, caused by the rapid radiation of 

 heat through the metal surfaces exposed to the inner and outer 

 air. No part of the metal frame of a greenhouse, excepting a 

 small portion of the gutter should be exposed to the outer air. 



For the glazing of houses having curvilinear roofs, I would 

 advise having the glass bent to fit the curves. This allows the use 

 of lights of glass twenty-four inches long, and insures a much 

 neater and tighter roof than can by produced by using man}' short 

 lights around the curves, as was done in times gone by. Many 

 think that the curved glass is very liable to breakage during hail- 

 storms, but experience has taught us the reverse, and this is 

 easil}' explained, as in the bending the glass becomes annealed or 

 toughened. 



Painting. We will now consider the painting of greenhouses. 

 This feature should receive close attention, as upon its use or 

 neglect rest in a great measure the durability and weather-proof 

 qualities of the structure. All parts should be well primed before 

 erection, the iron being scraped, or brushed witli stiff steel 

 brushes, to remove all scale, sand, or grease, and then coated 

 with a good quality of anti-corrosive paint and pure linseed oil, 

 using as little dryer or turpentine as possible. The wood, which 

 of course we assume to be perfecth' dry and clean, should be well 

 saturated with white lead of good quality and pure linseed oil, either 

 by dipping or by careful laying on with the brush. 



After erecting and glazing, the whole house, both iron and wood, 

 should receive two more coats of pure linseed oil and good white 

 lead, thinned with a little turpentine, one coat being perfectly (by 

 before the other is laid on. After the expiration of one full year, 

 the entire outside of the roof and glazed portions of the house 



