702 SUMMAKY OF CURRENT RESEARCHES RELATING TO 



Place a drop of balsam on the ground surface of the slide, pass it over 

 the flame of the lamp until sufficiently hard to chip when cold ; while 

 still hot, place the stone in position, press down as close as possible, 

 being careful not to enclose air-bubbles underneath. It is also im- 

 portant that the object be perfectly dry, as any moisture would cause 

 air-bubbles when placed in the hot balsam. This part of the process 

 should be carefully done ; for the object is now on its final resting- 

 place, and is not again to be disturbed. When the slide is cold, with 

 alcohol, or ether, clean away all the surplus balsam, return to the 

 glass slab, and grind down the other side of the section as thin as 

 desired, using the finest grade of emery in finishing. In this way 

 sections of almost any size and uniform thickness can be made 

 perfectly free from breaks and flaws. 



After the slide has been thoroughly washed and dried, it is ready 

 for the cover-glass. Place a drop of turpentine upon the object, 

 allowing it to spread entirely over it without excess ; this expels the 

 air and prepares it to receive the balsam. Next put a drop of balsam 

 on the cover-glass, and harden over the flame as before, only not quite 

 so hard this time ; let it cool a little, turn it over, and place the di'op, 

 which hangs suspended, upon the centre of the object ; heat the slide 

 again very slowly over the flame until the cover gradually settles to 

 its place, then gently press it home. When cold, clean away all the 

 surplus from around the cover, wash thoroughly with soap and water, 

 and the slide is finished. This process cannot be followed with any 

 other than the ground-glass slip. If the ordinary slip be used, the 

 object must be transferred from the glass upon which it is ground to 

 the slide upon which it is mounted, which, in very delicate sections, is 

 most difficult to do without breaking. 



Tin-foil Cells.* — Mr. A. H. Chester commends cells cut out of 

 dififerent thicknesses of tin-foil and finished on a lathe. 



The object is first fastened to the slide (centered on the turn- 

 table) by means of a weak solution of gelatin, gum-water, or Bruns- 

 wick black. For very small objects a small circle of the gelatin is 

 turned in the centre of the slide, and then allowed to dry. The 

 objects are arranged on the spot, and then, by carefully breathing on 

 the slide, they are fixed in position. If larger objects are to be fixed 

 to the slide, a spot of gelatin or gum that the object will entirely 

 cover is put on, and after drying, the object is fixed in the same way. 

 For larger and heavier objects a circle of Brunswick black is turned, 

 and after it has been thoroughly hardened by heat, so that when cool 

 a needle point will not mark it easily, the object is arranged on the 

 spot and fastened by warming again. 



In whatever way the object is fastened, the next thing to be done 

 is to lay the slide on the plate and heat it until it is perfectly dried 

 and ready to be covered. 



The slide is then centered on the table, and a circle of shellac, 

 which has been thickened and coloured with Chinese vermilion, is 

 run around the specimen, at such a distance from it that its inner 



* Amer. Mon. Micr. Journ., i. (1880) pp. 233-4. 



