ON MOUNTING. 149 



of the cover ; when this is hard, " ring " the cell 

 with two coats of white zinc cement, letting the first 

 coat dry thoroughly before applying the second. 

 To mount Diatoms in Canada Balsam, 



&C. Canada balsam has been, hitherto, universally 

 employed as the best medium in which to mount 

 diatoms. It has stood the test of time, and proved 

 fairly permanent and reliable. For the mounting 

 of diatoms, however, hardened balsam re-dissolved 

 in benzol or xylol is by no means so satisfactory in 

 its results as ordinary balsam, since it does not 

 admit of being submitted to the application of direct 

 heat, after the slide is mounted ; any attempt so to 

 harden the balsam resulting in the production of 

 air-bubbles, which carry away the forms in the 

 ebullition caused by the endeavour to drive out the 

 air, and without heat, applied directly, the balsam 

 never " sets " hard. Diatoms should therefore be 

 mounted in chemically pure, filtered balsam, diluted 

 to the consistency of cream with turpentine. The 

 diatoms in " strewed " slides should be allowed to 

 fall upon the cover from a " pipette" held at a 

 height of three or four inches above it the sudden 

 fall of the drop causing the diatoms to spread 

 evenly upon the surface of the cover. 1 The drop 

 upon the cover should then be dried, very slowly, by 

 means of a " Bunsen" burner placed underneath the 

 brass table upon which the cover (lying upon a 3 in. 

 by 1 in. slip) has been placed. When it is desired to 

 mount many slides of the same gathering of diatoms 



1 The even spreading of the diatoms on the cover will be 

 further ensured by breathing upon it before allowing the drop 

 to fall, whilst in selecting diatoms, if the cover upon which 

 they are to be placed is breathed upon, the forms will adhere 

 to it. 



