222 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



many instances to destroy all organic matter and to prepare for the 

 further step of separating the diatoms from coarse sand, Radiolaria 

 etc. Often, however, a third treatment is necessary, espe(^ially where 

 tlie percentage of organic matter is high and where clay is present, 

 llie tlurd l)oilmg is m concentrated commercial sulphuric acid As 

 much water as possible is extracted from the mass })y careful decanta- 

 tion and removal of the last drops with a pipette. The acid is then 

 slowly added, the quantity being about ten times the volume of the 

 mass and the whole is boiled in a porcelain evaporating dish over a 

 sand bath for one-half hour. At the expiration of this time powdered 

 potassmm cldorate is slowly added to the boiling acid until the black 

 color gives place to a gray or yellow. Very thorough washing follows 

 this to remove the last trace of acids and salts. In those instances 

 where a hne siliceous flock is present, this can be removed bv brincino- 

 the washed residue to a boil in a solution of soap, made -by adding 

 about 5 per cent of a saturated alcoholic soap solution to distilled 

 water. _ The soap water holds the flocculent matter in suspensioii and 

 a lows Its removal by decantation. As, however, very delicate forms 

 hke Chaetoceros, Nitzschia, etc., are liable to be lost hj this method 

 It IS to be used only where unavoidable. ' 



The coarse sand, Radiolaria, and like impurities are now removed 

 by rotating the material in a glass evaporating dish. By quicklv 

 revolving the lowest point of the dish in a small circle of, say, one^ialf 

 inch a pecuhar motion is given to the contents, on account of which 



mound 



center while the diatoms are held in suspension. The liquid is quickly 

 poured off from the sand, the process being repeated until the sand 

 IS found under the microscope to be free from diatoms. The cleaned 

 diatoms are then preserved in bottles in a 40 per cent solution of 

 alcohol with tlistilled water. 



_ In the preparations accompanying this report the diatoms were 

 picked up separately with a mechanical finger from strewn masses of 

 the cleaned material an<l mounted singly in the proper medium, gen- 

 erally Canada balsam. They are attached to the cover glasses of the 

 preparations by a delicate film of acetic-acid gelatin, and so placed 



slide. 



mmii 



Ihis mounting each specimen separately as^i labeled prepara- 

 tion, al hough involving much labor, was the only satisfactory method 

 of rendering available for future examination the forms herein 



described 



H 



tomaccous matei 



Cleve and Moller, are valuable; but every student consulting these 

 for identification must have felt the great inconvenience and uncer-^ 



anion 



the exact appearance of which is, umler the circumstances, not 



