GO MAI^MA' 



proceed thus, and if it has stood for some days perfectly undis- 

 turbed so much the better. The bottle is twirled rapidly, and 

 the lighter material rising up in the axis will soon diffuse itself 

 throughout the water. Allowing it to settle for two or three 

 seconds, until to the eye the grosser portions have just been 

 deposited, all that remains floating is now poured off into 

 another phial, and it is from this stock that we are to separate 

 the diatoms and sand from the clay and organic matter. The 

 material poured into this second bottle is allowed to settle 

 until the water simply appears milky or cloudy; the time will 

 vary according to the minuteness of the diatoms, and can only 

 be judged of from experience, say one minute, when all that 

 remains floating must be poured off, and thrown away, unless 

 there are very minute forms which it may be desirable to 

 separate. The phial is again to be filled with rain, or distilled 

 water (hard or lime water should be strictly eschewed), and 

 again shaken up. As soon as the heaviest deposit touches bot- 

 tom, the rest should be poured off into a third phial, leaving 

 say about one-fourth the amount behind in the second phial. 

 This third phial will now consist mainly of sand and diatoms, 

 with lighter organic matter and pure clay; the last two can be 

 removed by elutriation; for this purpose', fill the phial No. 3 

 with water, and after well shaking allow it to settle two to five 

 minutes, pour off and throw away the slightly milky water, and 

 repeat the operation, allowing it to settle a soniewdiat longer 

 time; the operation may be repeated a third time, wdien parti- 

 cles, suspended after an interval of eight or ten minutes, may 

 be poured off. Often, after the first settling of bottle No. 2, 

 the diatoms will rise more pure in the mass by twirling the 

 bottle than by shaking it up. A little practice and care will 

 enable any one to separate certain diatoms according to size. 

 1 had a gathering of J^eurosic/ma Spencerii from Scioto River, 

 O., sent to me, but although it had been chlorated, still, when 

 a mounting was made, not more than one or two frustules 

 would be in the field of view, the great mass being either 

 smaller forms, or fine fragments of silex; by careful watching 

 and testing the time when the different sizes would remain sus- 

 pended, I have made from this a preparation, which will show 

 hundreds where before were scarcely any, and which would 



