792 PKEPAKATION OF DIATOMS. 



others, as Synedra, Fragilaria, Melosira, Meridion, etc., if one wishes 

 to have a few frustules cohering together to show their habit, then 

 burning must be adopted, as the acid separates them joint by joint, and 

 valve from valve. This is accomplished by arranging the specimens 

 in the centre of a glass slide, and lajring them on a thin iron slide, and 

 placing the whole within a little iron tray, closed in the form of a 

 slipper, to exclude ashes. This is exposed to the fire tiU the slide is 

 red hot. The slide is now allowed to cool, and the specimen is ready 



Eig. 966. 



for being covered either with or without the intervention of balsam. 

 The latter is called dry mounting, and is best accomplished by making 

 a ring of asphalte, and following the same process as for liquid mount- 

 ing, but without liquid. When nitric acid is to be used, the cleaned 

 Diatoms are put into a large-sized test tube of German glass, with as 

 little water as possible, and about one part of nitric acid to four of 

 water. After being boUed for two or three minutes over a spirit-lamp, 

 the Diatoms must be allowed to subside, and as much liquor as possible 

 poured ofij with any fragments of vegetable matter floating in it. This 



Fig. 956. A case for containing slides after being prepared. There are three divisions, 

 each containing twelve slides, two of which are shown projecting above the lower division 

 of the box, the lid being hollowed to receive them. Numbers corresponding to those on 

 the slides are fastened on the partitions at the sides of the grooves which retain the slides. 

 On the front of the box a notice of the numbers contained in it should be fastened. Corre- 

 sponding numbers, with full particulars as to the preparations, ought to be entered in a 

 book, which serves as a catalogue, in which there should be first a numeral progressive 

 series, and then an alphabetical register for genera. Card boxes for holding 24 slides are 

 made by Smith and Beck, and others, price one shilling each. They are excellent for form- 

 ing a general collection. Cabinets are also made for slides, consisting of drjfwers half-an- 

 inch deep (including the bottom) divided so as to hold 30, 40, or 60 slides all on their back ; 

 the drawers being slightly bevelled at their divisions on one side, so that the slides may be 

 tilted up by pressing them down. Cases such as that in Figure 966 may be placed on their 

 ends, like books on a shelf, so as to keep the slides horizontal, and prevent the object from 

 gravitating to one side of the disc. 



