Proceedings of 

 the United States 

 National Museum ^^^^g^c^ 



SMITHSONIAN INSTITUTION • WASHINGTON, D.C. 



THE FREEZE-DRY PRESERVATION 

 OF BIOLOGICAL SPECIMENS 



By ROLLAND O. HOWER ^ 



Office of Exhibits 



Introduction 



Visitors today to the United States National Museum see specimens 

 of small animals that accurately represent the form and color they 

 possessed in life. This improved representation is the direct result of 

 the new method of specimen preservation that has been brought about 

 by the process of freeze-drying. By this process, the specimen 

 retains most of its original characteristics without further need for 

 preservation. 



This new technique is based upon sublimation of frozen fluids. 

 One of the earliest papers detailing the phenomenon of sublimation 

 was delivered to the Royal Society of London in 1813 by William 

 Hyde Wollaston, a physicist. Wollaston's commentary (1813) on 

 water passmg from the frozen to the gaseous state, apparently by- 

 passing the liquid phase, discussed what was already a well-known 

 phenomenon. It was not until the 1890's, however, that the removal 



1 As far as is known, Mr. Hower is the first to apply the freeze-dry process to 

 museum work. Developing more sophisticated apparatus and establishing time 

 schedules for the freezing of specimens, he is now investigating freeze-dry problems 

 of color retention, fat stabilization, and the freezing of larger specimens. 



1 



