THE CONSTRUCTION OF PLANT HOUSES. 95 



greenhouse is its attacliment to the potting house, and if this is 

 made fireproof insurance is unnecessary. The size of the potting 

 room depends on the extent of the glass. A very good way to 

 determine the size is first to ascertain the cellar space required for 

 the heaters and a winter's supply of coal, and this area will be 

 found in most cases to approximate a convenient size for the work 

 room. 



The cheapest way to construct a work room is to extend the 

 frame of the greenhouse over it, either covering it with glass or 

 substituting iu its place shingles or tin. The most common building 

 for this purpose is a one story frame structure, with shingle roof, 

 beveled or novelty siding, narrow matched beaded ceiling inside, 

 and Georgia pine or spruce floor, and provided with ample windows 

 for light, and potting bench and soil bins. In buildings which 

 have an area of two thousand feet or more a small office and seed 

 room partitioned off from the potting room are desirable. 



Discussion. 



Francis H. Appletou inquired as to the durability of iron posts 

 under the sills of greenhouses. 



Mr. Buruham replied that iron posts have been in common use 

 during the past five years ; and many have been used in this way 

 for ten years or more. These show some slight corrosion, but the 

 actual loss or waste is not appreciable. From observation of 

 similar uses of iron supports during longer terms, it is fair to say 

 that cast iron used for such supports is practically indestructible. 



In answer to another inquiry he said that the purposes of ven- 

 tilation are, to regulate the temperature, to get rid of deleterious 

 gases, and to introduce fresh air. 



To a question as to the feasibility of combining steam and hot- 

 water heating, Mr. Burnham replied that various machines are 

 found in factories which are supposed to do many things. But 

 experienced manufacturers always avoid such machines, as they 

 are generally unreliable in use for either purpose. The same 

 principle is involved in trying to heat a building with both steam 

 and hot water from one apparatus. The pipes cannot be fitted to 

 serve the double purpose as satisfactorily as for either alone. 



In regard to overhead heating, Mr. Burnham cited an instance 

 of a large building sixty feet high. When artificially heated by 

 steam coils on the floor at the sides of building there was but one 

 degree's difference in temperature at the floor and at the ridge ;, 



