8 PROCEEDIISrGS OF THE NATIONAL MUSEUM. vol. GO. 



persistently resists separation by decanting. It can generally be 

 removed by boiling in some thin colloidal solution, like soap solution, 

 the flocculent matter being thereby held in suspension while the dia- 

 toms are settling. By one or two such boilings and careful de- 

 cantations this silicious floe will be largely or wholly removed. Very 

 careful washing is required after this soap treatment before the 

 diatoms are put away in 35 per cent alcohol. 



However the author may have tried to make plain the different 

 steps in preparing diatoms for study, he recognizes that some con- 

 fusion may exist in the minds of students in regard to some parts 

 of this technic. A letter of inquiry, directed to him at the United 

 States National Museum, Washington, District of Columbia, will 

 receive an answer, in which the points in question will be more care- 

 fully explained. 



