286 How to p-epare Specimens of Diatomacese. 



Fragillarise, become too transparent if put up in this way, and 

 therefore another method of mounting 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 described, 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 densities. Of course, if some of this 

 sediment were to be mounted in this condition, extremely unsightly 

 slides would be procured ; so it is best to separate the finer 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 thoroughly cleaned, and a good-sized drop of water placed 

 upon the centre portion. A little of the diatom sediment is then 

 taken up in a dip-tube, and the point of the tube brought just into 

 contact with the drop. As soon as a few diatoms have run out of 

 the dip-tube, it is removed. Then a small splinter of wood or stiff 

 bristle is used to disseminate the diatoms through the drop of water 

 in such a way that they will be pretty evenly distributed and not 

 overlie each other. The water is then driven off by heat, a drop of 

 thin Canada balsam placed upon the dry diatoms, and a cover 

 placed on them in the usual manner. In many cases, especially 

 when dealing with the smaller forms, it will be found desirable to 

 mount them upon the cover in this same way, instead of upon the 

 slide, as they will then be brought as near as possible to the 

 objective of the microscope. Single or remarkable specimens of 

 diatoms may be picked out and mounted by themselves ; but the 

 manner of accomplishing this would occupy more space than it has 

 been thought desirable to devote to this portion of our subject, and 

 the reader is referred to the books on mounting microscopic objects 

 for the particulars of the process. 



The main principles of preparing and mounting Diatomaceae 

 for preservation and study have been given, and the intending 

 student will be able to devise modifications and improvements for 

 himself, so that he will be able to put up specimens in as finished 

 a manner as any to be procured from the dealers. — From the 

 Beport of the Geological Survey of New Hampshire, vol. i. 



