148 METHODS OP MICROSCOPICAL RESEARCH. 



bicarbonate of soda the disintegrated portions 

 being, from time to time, poured oft* into a beaker 

 and the boiling in bicarbonate of soda repeated 

 until all the deposit has broken up, when the 

 alkaline solution should be washed away and the 

 diatoms boiled for a short time in nitric acid all 

 traces of which are to be removed by repeated 

 washings and the forms kept in distilled water for 

 future use. 



To mount Diatoms " dry." All "dry" 

 mounts of diatoms, whether " strewed " or 

 " selected," are liable to destruction or deteriora- 

 tion from an accumulation of moisture upon the 

 under side of the cover, which moisture, sooner 

 or later, and in defiance of all precautions, always 

 makes its appearance. " Dry mounts " are there- 

 fore always more or less unsatisfactory and un- 

 reliable and to be avoided as much as possible. 

 The best method of mounting diatoms " dry " 

 whether for "test" or as "arranged" slides is 

 to make a cell of the best asphalt, of the necessary 

 thickness, by adding coat upon coat of the asphalt, 

 not by making the cell of sufficient depth at one 

 operation. Spread tbe diatoms upon the cover, if 

 necessary " burn " them, upon the cover, i.e., place the 

 cover upon a piece of thick platinum foil and raise 

 it, slowly and carefully, to a dull red heat over the 

 flame of a " Bunsen " burner; thoroughly heat the 

 slip with the asphalt cell upon it ; whilst it is hot 

 (and therefore certainly free from all damp or 

 moisture) place the, equally hot, cover carefully 

 upon the cell, pressing down the cover and making 

 sure that it adheres thoroughly and evenly to the 

 cell all round run a ring of asphalt round the edge 



