334 The Microscope. 



material. An occasional wet test under the microscope will show 

 whether the indications of diatoms are good; if so, the material is 

 then transferred to a small holder with a s];^ierical bottom, so that it 

 may quickly settle, and with a rubber bulb pipette, all water is care- 

 fully removed. Should there appear to be about a half -inch deep of 

 the material as the result of all previous manipulation, add to it an 

 equal bulk of sulphuric acid, intimately mix, and by the aid of the 

 pipette, transfer it to a half or three-quarter inch diameter glass test 

 tube of about six inches length, boil it for fifteen minutes over a 

 candle, or a spirit-lamp flame; in that length of time it is probable 

 that all organic matter therein will be reduced, or carbonized. At 

 this juncture, add carefully, a drop at a time, several drops of nitric 

 acid, and boil continuously for ten minutes longer, when it will soon 

 be noted that the blackness is discharged, restoring transparency to 

 the boiling fluid, a partial or complete bleaching of the material 

 and a remarkable reduction in volume. If there has not been a com- 

 plete reduction of all vegetable or other organic matter, it may be 

 necessary to add a few drops more of sulphuric acid and boil it a 

 while longer. Should the preparation at any time not yield satis- 

 factorily to the bleaching process, pour out the contents in a spheri- 

 cal bottom vessel, and allow time to settle, pipette off the acid, and 

 add a fresh quantity of sulphuric acid, and boil a few moments, 

 and finally add a few more drops of nitric acid to oxidize the remain- 

 der of the carlionized substances. 



All acid-boiling processes should be conducted in an open fire- 

 place if practicable, so that the irritating gases may pass up the 

 chimney and not vitiate the air of the room, or fill it with an unpleas- 

 ant odor. The above apparently long or double boiling process is 

 rarely required, but must be resorted to if the organic material to 

 be reduced is refractory. AYhere boiling first in sulphuric acid, and 

 later adding nitric acid is api^lied to the cleaning of all diatom gath- 

 erings not badly mixed with sand or vegetable debris, or, as applied 

 to the cleaning of pure gatherings, it acts very rapidly, giving 

 promptly a snowy white cleaning of the diatoms. In the case of the 

 marine or fresh water diatoms, a final bleaching may be accomplished 

 by pom'ing the diatoms while still in acid into a shallow and con- 

 tracted china or glass saucer, and adding thereto a few drops of 

 Darby's prophylactic fluid, which actively effervesces and liberates the 

 bleaching gas. While the boiling alone, first in sulphuric acid, and 

 later adding some nitric acid, will be sufficient, yet a greater white 

 ness is produced by the addition of the prophylactic fluid as a bleach- 



