James R. Kuppers
Pfeiffer College Misenheimer, North Carolina
1 . liah Capacity Vapor Traps
I
Vapor traps used in vacuum systems are uwally designed for efficient freezing out of traces of vapor. Less common applications are encountered in solid-vapor-solid distillation processes such as the "freeze-drying" of solutes or suspenoids. Conventional traps, when built to convenient dimensions with glass, have insufficientcapacities for this purpose. A "cold-finger" type trap is compact and easy to make. The conventional "cold linger" will clog within the t,ip of the central core if the radius of the core is very much smaller than that of the outer cylinder. If the radius of the central core is made progressively larger, a situation will ultimately prevail in which an ice mass between the outer cylinder and the central core clogs the trap. In either case the total volume of solvent which may he distilled prior to clogging is severely limited. This work was done while the author was a Summer Research Participant in the Chemistry Department of the University of BuR'slo, sponsored by the National Science Foundation G-15159. Mr. Joseph West fabricated the trap prototype and contributed valuable suggestions for the basic design.
242
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Journal of Chemical Education
The modified cold-finger diagrammed in the drawing has a core made of three concentric cylinders with porte connecting the space between each cylinder. The outside diameter of the trap is 6 cm. The ports are located near the top of the core so that the heat flux from the atmosphere keeps them free of condensate. There are three alternate paths for the vapor. The trap cannot clog until all three paths have been completely block~d. Futhermore there is a large ice collecting area over which the vapor intake is distributed. The capacity of the trap is about 165 ml of water prior to clogging. The trap construction cost was $18, a small fraction of the cost of commercially available freeze-drying trap? made from stainless steel.
