VII. QUICK-FREEZING AND FREEZING-DRYING 



219 



ago might have seemed fantastic. There are some commercial plants 

 capable of removing water from the frozen state in terms of thousands 

 of liters per day. During the war, all the plasma prepared from 

 blood collected by the American Red Cross for oin- armed forces was 

 dried from the frozen state for distribution. Some of the fractions 

 prepared from plasma by the Cohn procedure are freeze-dried. 

 Convalescent human serum, antitoxins and other antisera, bacterial 

 and viral vaccines, penicillin, streptomycin, parenteral vitamin prepa- 

 rations, and other products are dried by this process and are available 

 commercially. The principles involved in large scale freeze-drying 

 are the same as on a laboratory scale discussed in this chapter but, 

 of course, the manner of application varies considerably. This is be- 

 yond the scope of the present book and fuller discussion may be found 

 elsewhere (2). 



D. EQUIPMENT FOR FREEZING AND DEHYDRATING 



1. Sources of Low Temperature 



For quick-freezing, Dry Ice (solid carbon dioxide) suspended in a 

 bath of organic solvent such as ethanol, acetone, or the like is the 

 simplest and most readily available refrigerant for low temperature. 



Fig. 1. Freezing-drying equipment employing solid carbon dioxide (Dry Ice) 

 for general research. (Courtesy F. J. Stokrs Machine Co.) 



