114 



THE AMEEICAN MONTHLY 



[June, 



material is freed of all the flocculent 

 matter. It is surprising, sometimes, 

 to see the quantity of this. 



We now have the diatoms mixed 

 with fine sand. How are we to get 

 rid of the latter ? If there happens 

 to be coarse sand in the fresh material, 

 we may get rid of it by repeated 

 settlings and decantations before 

 boiling ; and should some remain at 

 the last washings after the boilings, 

 it may be disposed of in the same 

 way. But it is different with the fine 

 sand. Graduated settlings and de- 

 cantations have been advised ; but 

 these are insufficient, as, despite all 

 care, more or less of light silt will 

 float with the light forms of diatoms, 

 and the heavy diatoms will fall to the 

 bottom with the heavy sand. Whirl- 

 ing in an evaporating dish, has been 

 advised, but this is insufficient. I 

 have found no method better than 

 the one I have used for several years, 

 and which I have never seen des- 

 cribed or hinted, except in regard to 

 whirling. A few years ago, Mr. E. 

 Samuels of Boston, Mass., told me 

 he had used a method similar in some 

 respects. 



If the material contains the lighter 

 forms only, I first use whirling force 

 as follows : I take an evaporating 

 dish of a size according to the quan- 

 tity of material, and fasten it on the 

 wheel of my turn-table by means of 

 a narrow rubber band passed over it 

 and under the wheel. The material 

 is diffused in five or six times its 

 bulk of water. An empty, wide-mouth 

 bottle is near the turn-table and 

 should have a capacity of two or 

 three times the quantity of diffused 

 material. Shaking the material well, 

 I fill the evaporating dish about two- 

 thirds, and then whirl it with con- 

 siderable rapidity till I think the sand 

 has mostly settled at the bottom of 

 the dish, for the whirling motion 

 causes it to fall. I then pour off the 

 unsettled portion into the empty bot- 

 tle and add more of the material to 

 the sand and diatoms remaining in 

 the dish, and stir with a narrow strip 



of glass, the whirling is repeated ; 

 and so on with all the material. 

 When this has been done, water is 

 added to the portion in the dish and 

 the process continued till no diatoms 

 remain in the sand. To ascertain 

 this, the dipping-tube, again comes 

 into use. The material is treated in 

 this way several times, till no sand 

 can be obtained by it. If the material 

 contains heavy diatoms like the large 

 pinnularias, Triceratium favtis, and 

 heavy disk-forms, the whirling pro- 

 cess cannot well be used, for these 

 heavy forms fall to the bottom of the 

 dish with the sand. 



After the above process is ended, 

 I proceed as follows, and this is, in 

 most cases, the only method used 

 after the boiling and washings. I 

 have a slide of polished glass 3)^ 

 inches by 4j^ inches ; a smooth block 

 of wood 4 inches by 5 or 6 inches, 

 and 3 inches thick ; two wide-mouth 

 bottles of four to six ounces capacity, 

 with thin, projecting lips, one empty, 

 the other filled with the material thinly 

 diffused in water ; several pieces of 

 considerable size of old worn cotton 

 cloth, and, for I like it best, a clean 

 linen pocket-handkerchief, and a 

 small table. The table I place beside 

 my wash-bowl which is supplied with 

 water — not filtered in this instance — 

 through a pipe and faucet, and on it 

 are arranged my bottles, block and 

 cloths. I place the glass slide on the 

 block, taking care that the latter is 

 level, and, well shaking the material, 

 pour a little of it on the slide, and 

 then quickly pour it off, tipping the 

 slide so that the material will flow off 

 from a corner of it into the empty 

 bottle. The diatoms float off into 

 the bottle, and the sand adheres to 

 the slide. The slide is then washed 

 by letting water upon it from the 

 faucet, then wiped as well as may be 

 with one of the large pieces of cloth, 

 and then the surface to be used is 

 wiped with the linen handkerchief. 

 This last wiping dries the surface 

 thoroughly, and removes any little 

 shreds of cotton, which may have 



