MICR0L.1TER. DIVER TECHNIQUE 363 



keeping the diver in a moist chamber until time for adding the main 

 bottom drop. 



Should the biological object be so large that it cannot be trans- 

 ferred into the diver by means of a pipette, the diver is filled com- 

 pletely with the bottom drop solution, the diver is lowered into a 

 dish containing the object, and the object is led into the mouth of 

 the diver. Then the diver is placed upright and the object sinks 

 to the bottom. The excess solution is pipetted out, the outside of the 

 diver is dried and small rolls of lintless filter paper are used to dry 

 the inside of the diver neck, and finally the weight of the remaining 

 liquid plus the object is determined after a neck seal of paraffin 

 oil has been placed to prevent evaporation. 



To improve the visualization of the object in the bottom drop 

 during the pipetting, a drop of water is used to make a small piece 

 of cover slip adhere to the diver bulb after the diver has been 

 placed in the clamp stand. When the diver is in the thermostat, the 

 best view of the object may be had by using a cylindrical diver 

 or placing the object in a neck seal if this is possible. 



In order to remove an object from a diver without injury, the 

 neck of the diver is first rinsed as described on pages 364-365 ; then 

 the whole diver is filled with a suitable liquid, the diver is placed 

 in the dish intended for the object, and the object is allowed to 

 float or sink out of the diver. A slender pipette filled with the liquid 

 may be used to flush the object out of the diver. 



Wax Rings. There is great danger that the bottom drop will 

 creep up and be drawn into the capillary space between the stem 

 of the pipette and the diver neck when very small divers are used. 

 Proper centering of the pipette may not be sufficient to avoid the 

 difficulty. In such a case, a ring of beeswax about 0.5 mm. wide 

 is placed at the base of the diver neck. This will also prevent the 

 neck seal from creeping down. 



To place the wax ring an electrically heated platinum loop (Fig. 

 126) is used. When the diameter of the neck is greater than 1 mm., 

 carry out the following operation by hand: 



1. Heat the loop and fill it with wax. 



2. Allow to cool and place in the diver neck. 



3. Apply the ring where desired by heating to melt the wax and 

 rotating the loop to form a ring. 



4. Move the loop away from the glass wall and let it cool. 



