CALIBRATION WITH MERCURY 61 



acting. Moisture may be got rid of by sucking up 

 ether or alcohol. 



By using a measured volume of mercury, the graduation 

 may be made to correspond to a definite volume. For 

 instance, for Wassermann work the writer uses as unit 

 volume 20 cub. mm., which is obtained by measuring out 

 mercury with a hsemoglobinometer pipette, the volume 

 of which is 20 cub. mm. One c.c. of mercury weighs 

 13-5 grm. ; any volume may therefore be obtained by 

 weighing. 



For marking these pipettes grease-pencil or ink may be 

 employed. To render the mark more stable it should be 

 passed through the Bunsen flame. Blue-black ink heated 

 nearly to the softening point of the glass gives the most 

 stable marking. 



India-rubber caps. A few india-rubber caps for capping 

 test-tube or flask cultures are required. They retard 

 evaporation and the desiccation of the medium, and 

 prevent the entrance of moulds. For use they should be 

 soaked in 1-500 corrosive sublimate solution ; they 

 should not be kept in the solution, as vulcanised rubber 

 absorbs mercuric chloride (Glenny and Walpole). Tinfoil, 

 gutta-percha tissue (sealed down by warming) paraffin 

 wax, sealing wax, or plasticine may also be used to cover 

 the tops of tubes and flasks. 



Preparation of Sterile Test-tubes, Flasks, etc., for the 

 Reception or Manipulation of Culture Media 



To sterilise cotton-wool. Non-absorbent cotton-wool, 

 best or No. 2 quality is used for plugging purposes. The 

 wool should be pulled apart so as to assist the penetration 

 of heat ; in the compressed condition the interior is 

 difficult to sterilise. The loosened wool is placed in the 

 hot-air steriliser and the temperature is slowly raised to 



