Collection and Preparation of Diatom Material 



The Water Pollution Surveillance System plankton samples 

 used for diatom analyses are obtained from water plant intakes 

 or directly from rivers or lakes at one hundred and thirty stations 

 across the United States. The algae in the samples are concentrated 

 by centrifuging twenty minutes at 1000 x G. Several drops of 

 plankton concentrate are placed on a #1 coverglass, the coverglass 

 is dried cautiously to avoid splattering, and incinerated thirty 

 minutes on a hot plate at 1000 F. This treatment drives off most 

 of the organic matter present, leaving only the siliceous diatom 

 cell walls (thin-walled forms such as Rhizosolenia eriensis and 

 Melosira crenulata may be difficult to observe). A drop of Hyrax 

 mounting medium is placed in the center of a 75 nan x 25 mm glass 

 slide heated to approximately 200 F. When the solvent has evapor- 

 ated (the solvent-free Hyrax is hard and brittle at room temperature), 

 the coverglass bearing the incinerated diatoms is inverted and placed 

 on the drop of Hyrax, the slide is removed from the heat, and pressure 

 is applied to the coverglass until the Hyrax cools and hardens 

 (10 - 15 sec). The finished slide is examined at 970X. 



