NO. 3549 FREEZE-DRY PRESERVATION — HOWER 7 



per square inch. Sturdy construction is required if a chamber is to 

 withstand such force. 



At the Smithsonian, the structm-al requirements for the chambers 

 were met by the selection of a 60-gallon paint-spray pressure tank 

 for the specimen chamber and a 30-gallon tank for the condenser. 

 These tanks required modification but proved both satisfactory and 

 economical. 



The Smithsonian specimen chamber was mounted horizontally on 

 a base shaped to the contour of its walls, with allowance for the 

 thickness of an insulated outer plastic shell. The door on the Smith- 

 sonian chamber is two feet in diameter and withstands a total ex- 

 ternal pressure of 6780 pounds. The chamber itself, two feet in 

 diameter and 36 inches long, withstands a total external pressure 

 of a little more than 20 tons. 



Figure 4. — Detachable refrigeration assembly: A, outside view; B, inside view. 



The vapor line, a piece of steel tubmg with an inside diameter of 

 3^2 inches, was welded into a 3%-inch hole midway down the side of 

 the chamber. 



The inside of the chamber was lined with ^s-inch continuous copper 

 refrigeration tubing, filling one end and running the length of the 

 walls, where it was joined at alternate ends with 2-inch retiu-n bends. 

 The tubing was soldered to the steel wall of the chamber, and a 

 fillet of metaUic plastic compound was added to improve heat con- 

 duction between wall and tubing (fig. 3). 



