146 METHODS OF MICROSCOPICAL RESEARCH. 



gathering each time and allowing the diatoms to 

 settle before pouring off the water ; in this way all 

 soluble impurities can be removed. When the 

 water remains clear, after shaking, pour it off, 

 leaving the diatoms as nearly as possible dry ; cover 

 them to about one inch in depth with absolute 

 alcohol, or the strongest ordinary alcohol, which will 

 gradually dissolve and extract all the endochrome 

 from the valves ; change the alcohol daily until it 

 ceases to be tinged with green. Wash away all 

 trace of alcohol, pour off all water, place the diatoms 

 in a platinum capsule and heat them to a dull red 

 over a "Bunsen" burner; this will separate the 

 frustules into single valves, and complete the clean- 

 ing of the diatoms, which may be now bottled up 

 in distilled water for future mounting. 



To clean Diatoms growing upon Algse or 

 Shells. Place the algas or shell debris in a large 

 basin (in order to allow space for effervescence), 

 cover them with water, add gradually, hydrochloric 

 acid, and stir until violent effervescence results ; 

 add acid little by little, until effervescence ceases 

 thoroughly stirring from time to time strain 

 through net of sufficiently fine texture to retain the 

 debris whilst the diatoms pass through it. When 

 the forms shall have thoroughly settled down, pour 

 off all water and place the strained deposit in a 

 large test-tube. Boil in pure hydrochloric acid for 

 twenty minutes ; add pure nitric acid, and boil again 

 for twenty minutes. Whilst boiling add crystals of 

 chlorate of potash until complete bleaching results ; 

 remove all trace of acids and alkali by repeated 

 washings, and examine the forms ; if perfectly clean 

 bottle them up for mounting; if, as is sometimes 



