68 PREPARATION ANI> MOUNTING 



specimeua, 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 wetted 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 cf 

 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. Eylands always burns the diatoms 

 upon the glass at a dull red beat, 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- 



