OF MICKOSCOPIC OBJECTS. 97 



they may be dispersed over any space desired. When they 

 are thoroughly dry, drop a little balsam on one side, and 

 exclude the bubbles. The slide may then be warmed to 

 such a degree that the balsam, by lifting the glass at one 

 end, will be carried over the specimens, which may then be 

 covered with thin glass, made warm as before described. 

 Where the objects are quite dry, and loose upon the glass, 

 it requires great care in placing the cover upon them, other- 

 wise they are forced to one edge, or altogether from under 

 it, in the wave of the balsam. For this reason, Professor 

 Williamson adds a few drops of gum-water to the last 

 washing, which causes them to adhere sufficiently to the 

 glass to prevent any such mishap. 



Mr. T. G. Eylands's method differs in some degree from 

 the above, and is, to use his own words, as follows : Thick 

 balsam is preferable, and the burnt covers (see Chapter III.) 

 to be mounted are laid in a convenient position, with the 

 diatoms upwards. The slides required having been care- 

 fully cleaned and marked on the under side with a ring of 

 ink about half an inch in diameter by the aid of a turntable 

 to point out the centre, a drop of benzole is applied by a 

 large pin to the diatoms on the cover, so as to exclude the 

 air from the valves and frustules. The slide is then held 

 over the lamp, and when warm, a sufficiently large drop of 

 balsam is put upon it, and heated until it begins to steam. 

 If small bubbles appear, a puff of breath removes them, 

 The slide being held slightly inclined from the operator, and 

 the drop of balsam becoming convex at its lower edge, the 

 cover is brought in contact with it at that point, gradually 

 laid down, pressed with the forceps, and brought to its 

 central position. When cool the superfluous balsam (if 

 any) is removed with a heated knife-blade, the slide cleaned 

 with a little turpentine, and finished by washing in a hand- 

 basin with soap and water. In this process there is no 

 delay if the balsam be sufficiently thick, as the slide may be 

 cleaned off almost before it is cold. 



It is now well known that from common chalk it is an 



