THE BIOMETER: HOW TO USE IT TIg 
to admit air into the apparatus, and shut it. (Remove 
stoppers S and R; introduce a tissue to the right cham- 
ber B if performing an actual experiment, and replace 
the stoppers.) Seal the stoppers S and R with mercury. 
Turn stopcock L 180° to the right, so that three arms are 
now in communication. Shut stopcock J and open 
I very carefully and shut 7. (It should never be 
opened unless the nitrometer contains more than 
40 c.c. of air and stopcock J is shut.) Open J and 
shut J; open J and shut J. In this way we evacuate 
the chambers by opening J, and fill them up with 
pure air by opening 7. This process of washing the 
apparatus with air freed from carbon dioxide is repeated 
at least ‘five times. At the end of the last washing, 
having stopcock J shut and J opened, shut stopcocks Q 
and F. Without touching stopcock J open stopcock I 
and raise the safety bottle D,so that the pressure inside of 
the apparatus is now equal to that of the atmosphere, and 
then shut 7. Open stopcock C’; the mercury in the 
burette T should not move if the previous pressure 
adjustment with the safety bottle D and nitrometer is 
properly done. Shut the stopcock J so as to cut off 
suction; turn stopcock £ to right 90°, so that the space - 
between J and E will be filled with barium hydroxide; 
turn it 90° more to the right, so as to fill all the capillary 
T-tube below Q and F with the clear solution of barium 
hydroxide. Open stopcock Q very gently until a hemi- 
spherical drop of half-saturated barium hydroxide is 
formed at d. Then shut Q and make a similar drop at f 
in the other chamber. Turn stopcock L 45°, so that the 
connection between the two chambers is now severed. 
Shut stopcock C’. If the air is completely free from a 
