240 



MOUNTING OF OBJECTS. 



Built-up Cells. 



any one may put it into practice. A lonff strip of plate glass is 

 to be taken, whose breadth is equal to the desired depth of the 



cell, and whose length naust be 

 Fig- 6'3. equal to the sum of that of all 



its sides. This strip is to be 

 carefully bent to a right angle 

 in the blow-pipe flame, at three 

 points previously indicated by 

 marks so placed as to show 

 where the angles should fall ; 

 and the two ends, which will 

 thus be brought into contact 

 at right angles, are to be fused 

 together. Thus a large squai'e 

 well, slightly rounded at the 

 angles, will be formed ; and this, being very brittle, should be 

 allowed to cool very gradually, or, still better, should be annealed 

 in an oven. It must then be ground quite true on its upper and 

 lower edges, either on the lead plate with emery, or on a flat 

 stone with fine sand ; and it may then be cemented to a glass 

 slide in the usual way. 



138. Moimting Objects in Cells. — In mounting an object in a 

 cell, the first attention will of course be given to the cleanness 

 of the interior of the cell, and of the glass cover which is to be 

 placed on it ; this having been secured, the cell is to be filled 

 with fluid by the pipette or syringe ; and any minute air-bubbles 

 which may be seen adhering to its bottom or sides, must be 

 removed by the needle : the object, previously soaked in fluid 

 resembling that with which the cell is filled, is then to be placed ' 

 in the cell, and should be carefully examined for air-bubbles on 

 all sides, and also by looking up from below. When every pre- 

 caution has been taken to free it from these troublesome in- 

 truders, the cover may be placed on the cell, one side being first 

 brought down upon its edge and then the other ; and if the cell 

 have been previously brimming over with fluid (as it ought to 

 be) it is not likely that any air-space will remain. If, however, 

 any bubbles should present themselves beneath the cover, the 

 slide should be inclined, so as to cause them to rise towards the 

 highest part of its circumference, and the cover slipped away 

 from that part, so as to admit of the introduction of a little ad- 

 ditional fluid by the pipette or syringe ; and when this has 

 taken the place of the air-bubbles, the cover may be slipped 

 back into its place.^ All superfluous fluid is then to be taken 



1 Mr. Quekett and some other practised manipulators recommend that the edges of 

 the cell and that of the disk of glass be smeared with the gold-size or other varnish em- 

 ployed, before the cell is filled with fluid ; but the Author has found this practice ob- 

 jectionable, for two reasons, — first, because it prevents the cover from being slipped to 

 one side (which is often desirable), without its being soiled by the varnish, — and se- 

 cond, because when the edge of the cell has been thus made to " take" the varnish, that 

 which is afterwards applied for the closure of the cell is inore likely to run in, than if 

 the whole of the surface covered by the glass is moistened with water. 



