290 PRACTICAL MICROSCOPY. 



residue around the edge, leaving a clean slide of diatoms. 

 Never use hard water, for the lime in it will cause all 

 flocculent matter to cohere in masses. 



The methods given are all that is required for a large 

 proportion of diatomaceous material so far as disposing of 

 organic matter is concerned. The sand and other inde- 

 structible matter must be eliminated by gravity. 



Guano, Monterey stone, material containing lime, &c., 

 require harsher treatment and much more time. 



Guano should be boiled at least two hours in soft water, 

 or as long as any colouring matter can be turned off; then 

 proceed as in fossil earths. 



Stonelike masses must be broken down by boiling in a 

 strong solution of soda crystals. After disintegration wash 

 and boil for twenty to thirty minutes in strong nitric acid* 

 and while yet boiling add about an equal quantity of 

 muriatic acid, continuing the boiling for from twenty to 

 thirty minutes longer. After washing out the acids boil in 

 pure sulphuric acid until the mass becomes inky black, then 

 throw in fragments of bichromate of potash, and continue 

 the boiling until it becomes clean. If, on examination with 

 the microscope, it is found there is much flocculent matter 

 besides the diatoms and sand, it can be removed by boiling 

 for a few seconds in caustic potash, and then turning almost 

 instantly into plenty of soft water to destroy the action of the 

 potash. The diatoms are now chemically free from all organic 

 matter, and they may be dried and kept in small phials in 

 powder, or be put into equal parts of alcohol and water, 

 and kept for future separation from sand and other inorganic 

 matter, or we can proceed at once to isolate the diatoms, 

 also to separate into sizes. To do this, put the cleaned 

 diatoms into a small bottle, fill with soft water, filtered, and 

 after shaking thoroughly turn off all that floats after five 

 seconds into a larger bottle. Repeat the process, and after 



