FLUID MOUNTING. 223 



a piece of wood in a lathe. The cell is now filled with the mounting 

 medium, the object arranged, and the cover-glass pressed down. 

 All the excess of fluid from under the cover should be carefully 

 absorbed with blotting-paper until it is firmly held down by 

 capillary attraction. Now, with a hot needle and some small 

 scraps of D.I.P. cement, the edge of the cell should be sealed to 

 the cover-glass, a bit at a time, taking it just, and only just, over 

 on to the top of the cover. During this process it is necessary 

 at intervals to suck out more of the fluid with blotting-paper as 

 the cover-glass settles into its position. If this is not done the 

 liquid will come into contact with the hot needle and make a 

 bad joint. Should this occur the cement must be scraped o£E 

 for about the eighth of an inch on each side, the cover-glass dried 

 and resealed. This is a very important point, as the steam from 

 the hot liquid appears to have the property of preventing the 

 cement getting a hold on the glass. The angle between the 

 cover-glass and the ring must be completely filled up so that the 

 former is really embedded in the cell wall. The ring should 

 now be trimmed with a knife and the slide and cover-glass very 

 carefully cleaned. It may be left in this condition for a year or 

 so as a temporary mount. For a permanent mount it should now 

 be given two rings, at intervals of a day or two, of a spirit shellac 

 varnish to protect the wax from the solvent action of the next 

 ring, taking care to completely cover the whole of the D.I.P. 

 cement from glass to glass. 

 The shellac mixture used is : 



Best orange shellac . . . . .20 grammes 

 90 per cent, alcohol . . . . . 100 c.c. 



Dissolve and filter out the insoluble flocculent matter. This 

 is a slow process, and may be hastened by using a filter pump. 

 To the clear orange solution add : 



Castor oil . . . . . .1-8 c.c. 



Camphor 4-0 grammes 



and allow to evaporate to the right consistency. 



The camphor and castor oil remove brittleness and prevent 

 sweating. The whole slide, ring and cover should now be 

 thoroughly cleaned from wax and grease with xylol, the shellac 

 protecting the ring. 



After hardening for a week or a fortnight, several good rings of 



