15 



flame from a Bunsen burner. These operations must be repeated 10 

 or more times and the tube kept hot. Throughout these operations 

 the mercury is excluded and the funnel tube partakes at least partly 

 in the dryin<? influences. While the tube is kept quite warm and 

 the vacuum maintained at a high point the capillary is broken at 

 a and the mercury in M, which has been heated in the meantime, 

 is permitted to flow. M need not be large enough to contain all 



Figure 15. — Air-pump method of filling barometers 



the mercury required, but additions may be frequently made and 

 the whole kept quite warm. The filling will take place slowly, de- 

 pending upon the size of the bore of the inlet tube. The vacuum 

 must be maintained at a high point until the mercury fills the barome- 

 ter tube, when the flow may be stopped by admitting air to the pump. 

 The vessel M must also be removed if there is any tendency of the 

 mercury to flow one way or the other by gravitation. 



311681°— 41 ■h 



