36 



Glass. 

 The glass most largely used in the construction of greenhouses 

 is No. 2, or selected, double thick, for roof and southern walls, 

 while No. 3, double thick, may be used for north walls, partitions, 

 etc. The sizes used vary very much, but with the growing ten- 

 dency to increase the size. That most used is 16 x 24 to 20 x 30. 



Glazing. 

 All glass is put upon the sash bars bedded in soft putty that 

 shall allow the glass to press down upon tlie sash bars, filling up 

 every possible space with the least possible amount of putty. 

 Putty containing one-fourth to one-third white lead is, perhaps, 

 the best. All glass must be solidly fastened in with large zinc 

 points, small brads or other nails made for the special purpose. 

 The glass may be lapped from one-tenth to one-eighth of an inch 

 or it may be fitted together with or without the zinc strip. If 

 fitted without the zinc strip, glass should be square, and the lowest 

 edge of each light be thicker than the upper, as in Fig. 13, that 

 the water may run readily down the roof and not run into the 

 house. The use of the zinc strip (Fig. 14) makes a very close, 

 warm house, but with one with a low pitch of roof some water will 

 work under, and the condensed moisture on the inside will drip 

 more than when the glass is lapped or simply fitted together. The 

 frame should be thoroughly painted before the glass is set, again 

 after the glazing is done, and every second or third year, if it is 

 desired to preserve it the greatest length of time. 



Heating Greenhouses. 



This is by far the greatest problem in greenhouse construction 

 and there are many varying ideas in regard to it. The one thing 

 that must be secured is an abundance of heat for the crop grown 

 in the coldest weather, for nothing checks plants that are growing 

 rapidly so quickly as to have them chilled, — and even plants that 

 naturally grow at a low temperature may be seriously injured if 

 suddenly chilled after a period of very rapid growth at a high 

 temperature. 



Steam and hot water are about equally used in greenhouse heating, 

 the former being perhaps more largely used in heating large plants 

 while hot water is more used for small houses. The main advan- 

 tage of steam is that high heat can be gotten up more quickly 

 with it than with hot water, and much less heating surface of pipe 

 is required than with hot water, thus making the first cost of steam 

 equipment a little less than that of hot water. The advantages of 



