22 



MISC. PUBLICATION 679, U. S. DEPT. OF AGRICULTURE 



satisfactorily by placing the specimen layout in a drying box or cabinet 

 in which there is a suitable quantity of granular anhydrous calcium 

 chloride or a similarly effective desiccant (fig. 5). Best results are 

 obtained at room temperature, but moderate heat, up to 55° C. (about 

 130° F.), may be employed if desired to hasten the final stages. It 

 should be borne in mind, however, that if any appreciable amount of 

 moisture is present in a preserved specimen when it is heated, or if too 



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Figure 5. — Preserved specimens laid out on plastic sheets under temporary cover 

 films of cellulose acetate are dehydrated in a tightly closed box containing a suitable 

 desiccant. 



much heat is applied before all free moisture has been removed, dis- 

 coloration is likely to result. 



Three-stage drying. — It will be found convenient to use three drying 

 boxes and to transfer the specimen to each in succession as its dehydra- 

 tion progresses. The first-stage box, where it is allowed to remain 

 3 or 4 days, will contain partially hydrated desiccant material that 

 has been previously used, first in stage 3 and then in stage 2. Likewise 

 the second-stage box contains desiccant material that has been pre- 

 viously used in stage 3. A slightly longer period for the layout in this 

 box is usually desirable. The third-stage box will contain unused 

 anhydrous desiccant material. The layout should be left in this box 

 until practically all the free moisture has been removed from it. After 

 each lot of layouts has been transferred from one box to the next the 

 desiccant should be moved in the reverse direction and discarded after 

 use in stage 1 . 



