BY A. BCBAD EDWABD0. 31 



it can be laid upon an ordinary glass Blide, and examined I 



if it is worth preserving, which may be done in one or two 



ways: first, the glass cover is wanned, and a drop of 

 spirits of turpentine let fall upon it, covering the diatoms. 

 Just before the spirits evaporate, a small drop of thin Canada 

 balsam is added, and a slide taken, warmed, and a drop of bal- 

 sam placed upon the centre part of it. Then the cover is 

 brought down upon the slide, the two balsam-covered 

 together, in such a way, by tilting the cover slightly, that no 

 air is allowed to come between them, and the cover permitted 

 to fall gradually into place, driving a wave of balsam before it. 

 In this way we have the filamentous diatoms arranged as they 

 grow, but with endochrome removed, which would obscure the 

 markings, and in balsam, which renders them transparent. 

 Some forms, as some of the Fragillarice, become too transparent 

 if put up in this way, and therefore another method of mount- 

 ing must be adopted with them. They are burned upon the 

 cover, as just described, but mounted dry in air; that is to say, 

 a cell of gold size is made, the glass cover slightly warmed, and 

 then placed upon the cell, with the side upon which the diatoms 

 are fixed, downwards. The warmth slightly softens the gold 

 size, and the cover becomes fixed. 



Other forms besides the filamentous species may be mounted 

 in fluid, or burned upon the cover and subsequently put up in 

 balsam, or dry. But the commonest way of treating such 

 forms is to clean them by means of chemicals, as already de- 

 scribed, and then previous to mounting them divide the clean 

 gathering, consisting of a white sediment of Large and small 



diatoms along with fine sand, all mixed up together, into densi- 

 ties. 01 course, it* some of this sediment were to be mounted 

 in this condition, extremely unsightly slides would be procured; 

 so it is best to separate the liner from the coarser diatoms, and 

 these in turn from the sand. This is accomplished by what is 

 known as elutriation, or, separating into densities after the 



manner already described. Then slides may be mounted from 

 each of the densities in the following manner: A slide is thor- 

 oughly cleaned, and a g >od -i < d drop ^<i water plaoed upon the 



6 portion. A little of the diatom sediment IS then taken 

 up in a dip-tube, and tic I the tube brought just into 



