OF THE DIATOMACE^. 285 



When the cover-glass has become quite cool, place on the margin of 

 its edge a mere speck of Canada Balsam, the object of which is to 

 keep the cover^ with its surface covered with diatoms, face down- 

 wards, in the centre of the glass slip. By means of a pipette, 

 take a few drops of the solution of Phosphorus, and place them 

 on the edge of the circle, and by capillary attraction they will be 

 immediately drawn under, displacing the air in their progress. 



Having ascertained that the diatoms are completely immersed 

 in the medium, remove all superfluous particles of Phosphorus 

 with a piece of blotting-paper damped with Bisulphide of Carbon, 

 and consign it also to a basin of water. Finally, place the slide 

 on the turn-table, and with a brush dipped in Walton's Glucine or 

 Kay's Coaguline (the former we think the best) draw a ring round 

 the edge of the cover-glass. In all probability, this will be dry in 

 the course of about six hours, when if necessary another ring of 

 the cement may be added, covering this with a further application 

 of shellac varnish, or asphalt, and, as a last layer, any coloured 

 cement that the fancy of the operator may dictate. 



Diatoms that are almost indistinguishable in balsam show quite 

 clearly in this medium. The structure of Heliopelta and Ompha- 

 lopelta are brought out in a remarkable manner, and the same may 

 be said of many of the varieties of Naviaila, Pleiirosigma., and 

 Nitzschia. I am quite aware that the odour of Bisulphide of 

 Carbon and Phosphorus is by no means pleasing, but this the 

 operator must learn to disregard, as, since it " cannot be cured, it 

 must, therefore, be endured." 



As a precaution against burns from the Phosphorus getting 

 beneath the finger-nails, it will be well to anoint the hands with oil 

 or vaseHne. 



In closing this paper, I would make a slight reference to the 

 mounting of Diatoms in lines and patterns, which may be 

 done in two or three ways ; one of which is that a thin solution 

 of isinglass is made in hot water, and lightly brushed over the 

 centre of the slide, and when nearly dry the Diatoms are 

 arranged u],)on it, according to desire, the cover-glass is placed 

 upon it, and a drop of Canada Balsam in Benzole, or Styrax 

 in Chloroform is placed on the outer edge, when the air is 

 displaced by the incoming fluid, and the isinglass also dissolved 



