THE BIOMETER: HOW TO USE IT 119 



to admit air into the apparatus, and shut it. (Remove 

 stoppers 6 1 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 / and open 

 / 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 / and 

 shut /; open / and shut /. In this way we evacuate 

 the chambers by opening /, 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 7 shut and / opened, shut stopcocks Q 

 and F. Without touching stopcock / open stopcock 7 

 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 / so as to cut off 

 suction; turn stopcock E to right 90, so that the space 

 between / 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/ 

 in the other chamber. Turn stopcock L 45, so that the 

 connection between the two chambers is now severed. 

 Shut stopcock C f . If the air is completely free from a 



