573 
Bonnier and Mangin for the Analysis of Air. 
expelled, finally until a drop of mercury is seen to emerge from the end of 
the capillary tube in the potash solution. The potash is now blotted care- 
fully from the end of the capillary tube under the mercury, the air being 
driven slightly farther along at the end of the process to make sure that no 
potash is left in the tube. Now the air is drawn back into the bulb as 
before, the right meniscus again adjusted to the same point and the volume 
read ; as before, this is repeated a few times or until the readings are 
constant . 1 
The solution of pyrogallate of potash is drawn in fairly quickly in the 
same way as the potash solution. The air is brought, not too slowly, into 
contact with the film of solution. Fresh solution is drawn in and this time 
very slowly expelled. If much coloration is observed the film may be 
renewed a second time. Finally the left meniscus is moved to c, the tube 
blotted, and readings of the remaining volume obtained , 1 as before. 
1 N.B. A sudden alteration in the length of the air-thread during measurement means that the 
absorbing solution has been too quickly expelled ; too much has thus been left on the walls of the 
tube and has gradually collected at one point till it has broken the mercury thread there and altered 
the pressure of the air. This bubble of liquid must be expelled, and the end of the tube again 
blotted carefully before the reading of the volume is continued. 
