206 Modern Microscopy 



LESSON XII. 



CLEANING AND MOUNTING DIATOMS, 

 POLYCYSTINA, AND FORAMINIFERA. 



To Clean Diatoms growing upon Algae or Shells. — 



Place the Algae or shells in a basin, cover them with water, 

 add hydrochloric acid, and stir until effervescence results ; 

 add more acid little by little, until effervescence ceases, 

 stirring from time to time. Now strain through net of 

 sufficiently fine texture to allow the diatoms to pass, but to 

 retain the debris. Allow the strained fluid to settle down, 

 pour off the acid water, and place the deposit in a large 

 test-tube. Add pure hydrochloric acid, and boil for twenty 

 minutes ; add some pure nitric acid, and boil again for 

 twenty minutes, and, while boiling, add some crystals of 

 chlorate of potash until complete bleaching results. Ee- 

 move all trace of acid or alkali by washing in water, and 

 examine the forms under the microscope. If clean, bottle 

 them up in distilled water for future mounting. If, as is 

 sometimes the case, there has been animal matter present 

 which has not been removed, boil in pure sulphuric acid 

 for a few minutes. Wash away all trace of acid before 

 bottling the diatoms in distilled water. 



To Clean Fossil Diatomaceous Deposits. — Break the 

 deposit up into small pieces, and place them in a large test- 

 tube in a moderately strong solution of bicarbonate of soda, 

 and boil gently for two hours, the disintegrated portions 

 being from time to time poured off into a beaker and the 

 boiling in soda continued until all the deposit has broken 

 up. The alkaline solution must then be washed away, 

 and the diatoms boiled for a short time in nitric acid, and 

 when sufficiently clean wash away the acid in repeated 

 changes of water, and bottle up the diatoms in distilled 

 water. 



To Clean Living Diatoms. — Eemove all dirt or salt by 

 washing well in water ; shake well, and allow the diatoms 



