H. MOELAND ON MOUNTING SELECTED DIATOMS. / 



I have lately been turning my attention to tlie employment 

 of thin aluminium in lieu of copper as being free from the risk 

 of tingeing the balsam through becoming oxidized. I find that, 

 this metal can be obtained rolled in thin strips about three 

 inches wide, toVu i^i^h in thickness and upwards. This metal 

 as purchased is hard and elastic, and therefore requires to be 

 annealed, as otherwise it would be difficult to properly flatten 

 the cupped discs after they leave the die. I find it can be 

 annealed and rendered very similar to thin copper to the touch 

 by simply moving the thin metal to and fro in the flame of a 

 spirit lamp, taking care not to burn the metal by overheating. 

 It will be known when this process is complete by the behaviour 

 of the aluminium when handled by being passed between the 

 fingers. For general use I consider that discs of from '002" to 

 •003" are amply thin enough, but I have prepared some as thin 

 as Y2V0" ^^^^ ^^ thickness. These latter, however, I could only 

 use in very exceptional cases. 



In lieu of metal discs thin glass squares can be employed, but 

 it is difficult to obtain sufficiently thin glass. To cut very small 

 squares, viz., of -^^ inch, or even as small as ^Jy inch, fasten a 

 piece of thin glass on a square piece of brass by means of tallow ; 

 then, if this piece of brass be fixed just below the surface of a 

 planed board, the glass can be cut up as desired by means of a 

 writing diamond and a marquois scale and square. Remove 

 the cut-up glass by heat, and boil the small glass squares in 

 soda and water to get rid of the tallow. 



As the surface of glass slips is very often far from being all 

 that could be desired, it is as well sometimes to first mount a 

 cover on the slip, and arrange and fix the diatoms on the upper 

 surface of this cover-glass, finishing up with a smaller cover. 



It must by no means be supposed that I have given up 

 mounting on the underside of cover- glass. 'I still continue to 

 do so in the majority of cases, only adopting the method now 

 described when thought advisable. 



