<52 PREPARATION AND MOUNTING 



place), they may be placed in a small phial with a little 

 Distilled water. 



There are many cases in which the above method will not 

 effect a perfect cleansing, as certain substances with which 

 diatoms are frequently mixed are not soluble in nitric acid. 

 For this reason the following method is resorted to : Take 

 a, quantity of the matter containing the DiatomaceaB and 

 wash first with pure water, to get rid of all the impurities 

 possible. Allow this to settle perfectly and decant the 

 water. Add hydrochloric acid gradually, and when all 

 effervescence has subsided, boil for some minutes by aid of 

 the lamp. When cool and the particles have subsided, 

 decant the hydrochloric and add nitric acid. The boiling 

 must then be repeated until a drop of the liquid when 

 placed under the microscope shows the valves or " frustules " 

 clean. After allowing the diatoms to settle, the acid must 

 be decanted, and pure water substituted. The washing 

 must be repeated as in the former process . until all the 

 remains of crystals or acid are removed, when the specimens 

 may be preserved in small phials. 



Such are the usual modes of treating the Diatomaceae, 

 but there are certain cases in which particular methods are 

 required to give anything like perfect results. Persons of 

 great experience combine a variety of treatments, and thus 

 obtain better and more uniform specimens. Perhaps it will 

 be advantageous to give the young student the process 

 adopted by one of the most successful preparers of these 

 objects; but I will first state the different methods of 

 mounting the cleaned diatoms dry : how to employ Canada 

 balsam and fluid in their preservation will be elsewhere 

 described. 



It was before stated that diatoms when cleansed might 

 be preserved in small phials of distilled water. When re- 

 quired for mounting, shake the phial, and with a thin glass 

 tube or rod take up a drop of the fluid and spread it upon 

 the surface of the slide in the desired position. This must 

 be allowed to dry gradually, or by the aid of the lamp 



