156 



COMMERCIAL POULTRY RAISING 



of a light spring "B." The trigger "C," made from a piece of 

 metal, preferably brass, since that material will not rust, engages 

 a trip or cleat "D," when the platform is set. This cleat is also 

 made of metal and is screwed to the door proper. It is not neces- 

 sary for this part to be of brass, particularly if the trigger "C" 



"p" 



"c- 











"Fi-nTTOTiri-fl 



rzr 



^ 



^ T"l.oot=< 



■i-^^BSi.'.iJ^'^ 



STTilNSI HIINgE-/ 







SECTION "TH-ROUc^H 



T=i_^-rTOT^r-l 



M 



Fig. 109. — Details of a self-rising door. 



is composition, since brass against steel makes a good bearing 

 surface. 



If a swinging door is used, it should be hinged on the outside 

 of the building, using spring hinges similar to those commonly 

 found on screen doors; but, of course, the hinges must be reversed 

 so that the action of the door is to open outward instead of in- 



