D. B. WARD, M. D. 81 



the weeds are particularly rich in diatoms some of them 

 may be put iu the bottom of the pail and carried home. 

 Wherever there is tide- water, as in the river here, col- 

 lections should be made at low water ; scrapings from the 

 dock timbers and stones which are covered at high water 

 often yield immense numbers of fine specimens. The 

 mud in the coves along the river too often has an abund- 

 ance of living and dead diatoms. This latter (the mud) 

 is hard to clean or rather the x^i'ocess is a very tedious 

 one and is conducted as follows : A portion of the mud — 

 say about an ounce — is put into a wash basin, which is 

 then filled with water and allowed to stand for about a half 

 hour, when the water is carefully decanted close to the 

 surface of the mud, the basin refilled with water and the 

 process repeated until the water will settle clear in one- 

 half hour. Now this will take from two days to a week. 

 Then the remaining mud being transferred to a glass 

 beaker after the water has been poured off close, sulphuric 

 acid in equal or greater bulk is added, after which bi- 

 chromate of potash is added until all action ceases. As 

 this action is very energetic if much organic matter be 

 present, the bichromate is added a little at a time. The 

 beaker is allowed to stand an hour or two, when the wash- 

 ing is resumed and continued until the acid is all washed 

 out. There should be, if the process has been thoroughly 

 done, only diatoms and sand left — too often a few dia- 

 toms and a great deal of sand. The diatoms are sepa- 

 rated by putting a small quantity with water in a two- 

 ounce beaker or a thin liquor glass and allowing it to 

 settle. When the water is perfectly clear a very slight 

 rotary motion is given to the beaker and the diatoms 

 come up in a little cloud and the sand remains on the 

 bottom. They are then removed with a large pipette, 

 more water is added and the process repeated until noth- 

 ing but sand is left in the beaker. This looks easy but ic 

 is not, and requires a good deal of judgment, as the heavy 



18 



