THE BIOMETER: HOW TO USE IT 119 



t6 admit air into the apparatus, and shut it. (Remove 

 stoppers 5 and R; introduce a tissue to the right cham- 

 ber B if performing an actual experiment, and replace 

 the stoppers.) Seal the stoppers 5 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 /. (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 /. 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 / shut and / opened, shut stopcocks Q 

 and F. Without touching stopcock / open stopcock / 

 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 



