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®n tbe Collection anb preparation of 



tbe ©iatomacea^* 



By Alfred W. Griffin. 



Part II. — Preparation. 



HAVING accumulated a number of gatherings and rough 

 material which contain specimens of Diatomaceae, the next 

 step is to clean and preserve the Diatoms for future use 

 and study. If any microscopist wishes to mount a few slides, the 

 process of cleansing by Nitric Acid is certainly the easiest, and 

 there is no necessity to refer further to it here ; but I would add 

 that whilst occasionally very clean specimens may be obtained, 

 yet, in the majority of cases, they are far from satisfying the critical 

 eye of the experienced mounter. A few of the most approved 

 and satisfactory methods I will now mention, remembering that 

 even these will have to be modified according to the nature of the 

 materials to be operated upon. These materials, for convenience 

 sake, I will divide into the following series :^ recent gatherings ; 

 muds ; guanos ; lacustrine, marine, and fossil deposits. 



In recent gatherings, there will, in all probability, be a large 

 quantity of sand or other earthy admixture which it will be as well 

 to remove before commencing to use the acid. This is best ac- 

 complished by pouring clean water upon the gathering, and then 

 decanting off the supernatant fluid ; the siliceous particles being 

 the heavier, will have fallen to the bottom of the glass, which should 

 be of a conical shape. After an interval of about two hours the 

 water containing the diatoms should be examined, and when it is 

 found that they have subsided to the bottom of the glass, so much 

 as is possible of the fluid should be poured off from the sediment, 

 leaving it nearly dry. The Diatoms must now be transferred to 

 a strong test tube, and covered with Nitric Acid to the height of 

 an inch. Effervescence usually takes place in a few minutes, and 

 it will be well to wait until this subsides. The test tube is then to 



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