68 PREPARATION AND MOUNTING 
specimens, which is desirable, is not obtained. In order to 
effect this, let a drop of the cleansed gathering be diluted 
sufficiently for the purpose—how much must be determined 
in each case by experiment—and let the covers to be 
mounted be cleaned and laid upon the brass plate. (See 
Chapter II.) By means of a glass tube, about one-twelfth of 
an inch in diameter, stopped by the wettéd finger at the ~ 
upper end, take up as much of the diluted material as will 
form a moderately convex drop extending over the whole 
cover. When all the covers required are thus prepared, 
apply a lamp below the brass plate, and raise the tem- 
perature to a point just short of boiling. By this means 
the covers will be dried in a few minutes, and the specimens 
equally distributed over the whole area. The spread of 
the fluid upon the covers is facilitated by breathing upon 
them; and, to insure uniformity, care must be taken to 
avoid shaking them whilst drying. The best plan is to 
mount at least half a dozen at once. 
Before mounting, Mr. Rylands always burns the diatoms 
upon the glass at a dull red heat, whether they are used 
with balsam or dry. This burning, he says, is not only 
an additional cleaning process, but it effectually fixes the 
diatoms, and prevents them floating out if mounted with 
balsam. The thinnest covers may be burnt without damage 
if they are placed upon a small piece of platinum foil ot 
the size required, which should be about one-hundredth of 
an inch thick, perfectly flat, and having three of its edges 
slightly bent over, so as to prevent its warping with the 
heat. The small flame of a spirit-lamp, or, where there is 
gas, a Bunsen’s burner, may be employed. The cover _ 
should be shaded from direct daylight, that the action of 
the flame may be observed more perfectly. Care must then 
be taken to raise the temperature only to the dull red heat 
before mentioned. The cover will then be in a fit state for 
mounting as required. 
It has been stated in another place that it is assumed 
that the operator is not mounting diatoms simply as micros- 
