THE CONSTRUCTION OF PLANT HOUSES. 87 



per foot. The top of the sill is beveled so that it does not hold 

 water, aud is provided with a stop cast on solid for the ventilator 

 or sash to close against. 



The wrought iron rafter is formed of refined bar iron from ^ by 

 3 inches dimensions for small houses, twenty feet and less m 

 width, to ^ by 6 inches for houses having a fifty feet span. This 

 iron can be had in any lengths desired and can be bent to the 

 shape of the roof, cold, by means of a screw or hydraulic press. 

 No matter what the shape of the roof, this supporting rafter can 

 be bent or welded to conform to it, giving equal strength with a 

 simple straight line house. Purlins are placed laterally between the 

 rafters about four feet apart. These are made of wrought iron 

 bars or angles aud serve to brace the rafters sidewise ; also for 

 the support of the light sash bars and glass. In joining the 

 purlins to the rafters care must be taken to allow for the expansion 

 of the metal and some special provision must be made for it, as, 

 when the sun shines directly upon the iron, it has been known to 

 expand nearly ^ inch in an ordinary length of purlin. Such- an 

 expansion in each purlin in a house one hundred feet long would 

 amount to a total increase in the length of between one and two 

 inches, aud would cause certain destruction to the glazing and 

 other parts of the structure. In this connection the experience of 

 one of the proprietors of an important New England iron works 

 may be of interest. He stated that his father, who was an expert 

 engineer and had established the works many years before, had 

 built himself an iron framed greenhouse. The first season it was 

 ruined by contraction and expansion of the metal. "With this 

 experience as a guide he attempted to remedy the trouble, and 

 made extensive changes to cure the defects, when it was again 

 badly damaged. This time he gave it up and rebuilt it with wood, 

 saying that an iron frame was not adapted for greenhouse 

 purposes. This old wooden greenhouse, after standing many 

 years, was replaced by one of the modern iron constructions with 

 entirely satisfactory results. The amount of wood used in this 

 construction for sash bars, caps, sashes, doors, etc., is very small, 

 and as no weight or strain of the building depends on any piece of 

 it, and as each piece is itself supported by the iron frame, a very 

 long time must elapse before any repairs are needed ; but when 

 that time comes any part of it, or all, can be readily renewed. 



