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i ini'.r 1 -ii'Ns i'i:«»M nil. NATIONAL HERBARIUM 



many instances to destroy all organic matter and to prepare f<>r the 

 further step of separating the diatoms From coarse Band, Radiolaria, 

 etc. Often, however, a third treatment la necessary, especially where 

 the percentage of organic matter la high and where clay ia present. 



The third boiling ia in concentrated commercial Bulphuric acid. A- 



much water as possible ia extracted from the ma— by careful decanta- 

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

 -and hath for one-half hour. At the expiration of this time powdered 

 potassium chlorate i- -lowly 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 iA' acid- anil -alts. In those instances 

 where a line siliceous Hock is present . t hi- can he removed by bringing 

 the washed residue to a boil in a solution of soap, made 1)\ adding 

 about 5 per cent o{ a saturated alcoholic soap Bolution to distilled 

 water. The soap water holds the lloccnlent matter in suspension and 

 allow- its removal by decantation. As. however, very delicate forms 

 like Chaetoceros, Nitzschia, etc., are liable to he lost by this method, 

 it i- to he used only where unavoidable. 



The coarse -and. Radiolaria, and like impurities are now removed 

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

 revolving the lowest point of the dish in a -mall circle of. -ay. one-half 

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

 the large sand and other coarse ingredients collect in a mound at the 

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

 poured oil" from the sand, the process being repeated until the sand 

 i- found under the microscope to be fi'cc from diatoms. The cleaned 

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

 alcohol with distilled water. 



In the preparations accompanying this report the diatom- were 

 picked up separately with a mechanical finger from strewn masses <>f 

 the cleaned material and mounted singly in the proper medium, gen- 

 erally Canada balsam. They are attached to the cover glasses <>f the 

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

 a- to occupy the center of a minute ring <>f india ink spun on the glasa 

 slide. This mounting each specimen separately aa a labeled prepara- 

 tion, although involving much labor, was the only -at isfactory method 

 of rendering available for future examination the forms herein 

 described. Strewn slides of diatomaceoua material containing cer- 

 tain .species, like the II. L. Smith type slides and most of those of 

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

 for identification must have felt the great inconvenience and uncer- 

 tainty of hunt ing among a mass of mixed diatoms for a certain specie-. 

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



