10 



SCIENTIFIC AND APPLIED PHARMACOGNOSY 



decolorizing and clarification value of different specimens depending 

 on the various forms of diatoms present and their condition. 



The forms of diatoms present may be readily studied in mounts 

 made with water or solutions of hydrated chloral. In special cases 

 the material may be cleared for microscopical examination by first 

 thoroughly mixing it with nitric acid and then adding a crystal of 



FIG. 3. jSome common forms of diatoms found in Diatomacequs earth. A, a 

 species of Cymbella; B, Tabellaria floccolsa ; C, another species of Tabellaria; 

 D, two views of Navicula viridis; E, Navicula Phoenecenteron ; F , Navicula 

 lacustris; G, Synedra Ulna; H, several frustules of a Navicula; J, Gom- 

 phonema geminatum; K, a species of Stauroneis; L, Epithemia Hynd- 

 mannii; M, some frustules of Epithemia; N, Pinnularia Brebessonii; 0, 

 Eunotia diodon; /, fragments of broken diatoms. Identified by Chas. 

 Boyer, drawn by W. F. Haase. 



potassium bichromate. The mixture is then gently heated and the 

 reaction allowed to continue for ten or fifteen minutes. The acid 

 solution is then carefully decanted and the residue washed repeatedly 

 with distilled water until practically free from acid. In some cases 

 the diatomaceous material is boiled with solutions of potassium 



