PREPARATION OF DIATOMS FOR STUDY 



The preparation of diatoms for study involves: 1) Washing sand 

 or mud, or macerating and flushing materials ( water weeds, moss- 

 es, etc. ); 2) separating diatoms from debris; 3) boiHng in acid 

 and potassium dichromate; 4) washing; 5) drying and mounting in 

 Hyrax. Various and modified techniques may be used. 



A simple procedure that is suitable for general purposes or 

 for casual study is to make a thin smear of diatomaceous material 

 on a microscope slide in copious water. This is held over a flame 

 and cooked' until dry and charred. The smear can then be stirred 

 in a drop of water or water and glycerine and remounted under a 

 cover glass 



The essentials of a more involved technique are as follows: 1. 

 Shake sand or other material vigorously. Allow the coarse material 

 to settle for a few seconds, and then the top water is poured off 

 while it is still swirling. Repeat several times. 2. Use small aH- 

 quots of the washed material and wash these again, collecting in 

 a clean evaporating dish or small jar. 3. Dry the washed material 

 in an evaporating dish. 4. After drying pour on nitric acid and 

 boil (carefully) until the acid ceases to fume. 5. Add 2 or 3 crystals 

 of potassium dichromate. 6. Boil this mixture again and cool. 

 7. Pour off acid into a waste acid jar (not water), saving the 

 material in the bottom, and cover with sulphuric acid. 8. Boil for 

 several minutes and again add two crystals of potassium dichromate. 

 In this boiling process it may be desirable to repeat or to add a 

 little fresh acid a time or two. 9. Cool and then pour off acid 

 into a waste jar. 10. Rinse the sediment in several waters, stirring 

 it and allowing it to settle. 11. Swirl vigorously and pour off the 

 top water so as to ehminate as much remaining sand as possible. 

 12. Collect several aliquots treated as above in a jar and repeat 

 the swirhng-rinsing-pouring until acid has been removed. 13. 

 Place the washed material in an evaporating dish of water and 

 bring to a boil. Then add a small piece of sodium hydroxide ( a 

 lump about 1/2-inch long is sufficient). 14. Continue to boil for 

 not more than 3 minutes. 15. Rinse and rewash two or three times 

 to remove all the hydroxide. 16. The material can then be rewashed 

 and poured into watch glasses or preserving vials, or spread on 

 slides where a smear is allowed to dry. A drop of Hyrax or other 

 mounting medium can now be added to the smear and a cover 

 glass put in place. 



[941] 



