6 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 119 



Instrumentation of the Freeze -dry System 



The basic equipment necessary to establish a freeze-dry apparatus 

 consists of a specimen chamber, a condenser chamber, and a vacuum 

 pump. The Smithsonian system also incorporates refrigeration con- 

 trol components that are very desirable for maintaining the depend- 

 abihty of the system. 



Figure 3. — Continuous copper tubing (% in.) connected at alternate ends by return bends 

 within tlie specimen chamber. 



Specimen chamber. — The basic requirements for the specimen 

 chamber are that (1) it must be vacuum tight; (2) it must be refrig- 

 erated; and (3) it must have a large access opening. 



The ultimate vacuum within the chamber can be as low as 10 

 microns (1X10"^ mm. Hg.) of pressure, producing a differential 

 between internal and external pressure of approximately 15 pounds 



