LIFTING DEVICES 



91 



by side. The side of the tray rests on the projecting portion 

 above s. One line of the dogs is raised by the head -block and the 

 tray is lifted with it, the side of the tray as it rises forcing in the 

 dog above it. As the tray passes the dog, the latter falls out by 

 its own weight and the tray rests upon it, whilst the head -block is 



Fig. 18. Topping portable evaporator. 



let go, and the movable line of dogs falls back to its place. This 

 is not the form of catch or dog which was used in the original 

 Cassidy apparatus, for in that the catches evidently worked by 

 springs and not by gravity. The brief of the original specification 

 called for f the combination of stationary posts provided with 

 spring- catches, with vertically -movable posts carrying drying- 

 frames and provided with ^similar spring- catches, and with mech- 

 anism for operating the same.' (See U. S. Gazette of Patents, 

 ix. 165, 166.) 



