THE BIOMETER: HOW TO USE IT 117 



with a less concentrated alkaline solution (a weaker 

 solution is necessary so that the chamber may be filled 

 with air which is not too dry). Driving the air into 

 the nitrometer is accomplished either by increasing the 

 pressure in carboy F, by introducing more alkali from the 

 carboy above E, or by introducing more alkali through 

 funnel instead of from another carboy. After each 

 evacuation of the apparatus by a strong suction this 

 air free from carbon dioxide is introduced from the 

 nitrometer C or W into the chambers through the stop- 

 cock 7. For ordinary experiments one can keep the 

 pressure in the carboy F high enough so that air free 

 from carbon dioxide can be driven into the nitrometer 

 simply by opening stopcock 9 after each evacuation. 



How to test purity of air. -In order to test whether 

 or not the air in carboy F is free from carbon dioxide 

 the following experiment is necessary. It may be 

 stated that in all ordinary experiments we use exactly 

 the same manipulation as the one now to be described. 

 When the apparatus is perfectly dry, the pump being 

 at work, open stopcock (or pinchcock) 9 so that the 

 nitrometer is filled with the air freed of carbon dioxide 

 from carboy F. (If no bubbles come out by opening this 

 pinchcock it means that there is not enough pressure in 

 the carboy. In that case open pinchcock 8 to let more 

 alkali siphon down from the carboy above E, until 

 about 200 to 300 c.c. of air can be obtained by opening 

 pinchcock 9.) 



Shut stopcocks C and C' and /. If the pressure 

 pump is strong enough and all the joints are tight, 

 chambers A and B should be under a strong negative 

 pressure by now, so that when you open stopcock C 



