THE MANOMETERS. 47 



mercury in the other direction. When the bulbs and more or less 

 of the tube B have been filled, and the junctions at d and E have 

 been made, the manometer is repeatedly washed out with air which 

 has been dried by resublimed phosphorus pentoxide. For this pur- 

 pose, by lowering the reservoir (i), the dried air is admitted through 

 the stopcock at the top, and likewise through /, which is also provided 

 with a drying tube. By raising i, it is again expelled, mostly through 

 g, but partly through /. 



The next step, after drying the manometer, is to fill it with nitrogen 

 from the reservoir (A). The reservoir (i) is raised and the air in the 

 manometer is expelled through g until the mercury column reaches j, 

 when the stopcock (h) is closed, and a small quantity of mercury is 

 driven into the side tube (/). This is the mercury which is afterwards 

 to occupy the upper end of the closed manometer. The rubber tube 

 connecting/ with its drying tube is tightly closed and the air remaining 

 between j and the stopcock (h) is expelled through h, care being taken 

 not to allow the mercury quite to reach the stopcock, lest it should be 

 contaminated by some of the lubricant on the latter. Some of the 

 nitrogen in A is repeatedly wasted through the stopcock at the top and 

 through g in order to remove any air still remaining in the upper part 

 of the apparatus. Then by lowering i or raising I, with stopcock k open, 

 the manometer is filled with nitrogen. This is wasted through g, and the 

 manometer is again filled from A , and the operation of filling and empty- 

 ing it is repeated as many times as may be thought necessary. 



When the manometer has been filled with nitrogen for the last time, 

 the reservoir (i) is adjusted to the right level, and the gas is placed 

 under a slight over pressure by raising I. The stopcock (h) is opened 

 and then quickly closed. This leaves the nitrogen in the manometer 

 under a pressure equal to that of the atmosphere. 



By gently pinching the rubber tube which closes/, a little mercury is 

 forced out of the side tube into the vertical one between j and d. If it 

 breaks into globules at j, they are reunited at d by tapping the tube. 

 The mercury thus transferred does not enter the manometer, because 

 of its small bore. 



The reservoir (i) is now lowered until all the mercury collected at d 

 has been drawn into the manometer to some convenient distance below 

 that point, when the glass at d is softened in the blowpipe flame and the 

 manometer is detached, but so as to leave both tubes sealed. 



The glass at the detached end of the manometer is again softened in 

 the flame and then drawn out to an exceedingly fine capillary tube, 

 which is afterwards filled with mercury by raising i. Finally the capil- 

 lary is closed in the flame, and the walls are thickened under slightly 

 diminished pressure. Care must be taken, in closing the manometer, 

 not to convert any considerable amount of the mercury into vapor, 

 and to heat the glass so uniformly that the vapor which is necessarily 



