46 



OSMOTIC PRESSURE OF AQUEOUS SOLUTIONS. 



The nitrogen used in the manometers is obtained by passing air first 

 through an alkaline solution of pyrogallol, and then, in the order named, 

 over heated copper oxide, heated copper, heated copper oxide, cal- 

 cium chloride, fused potassium 

 hydroxide, and resublimed phos- 

 phorus pentoxide. The glass 

 tubes containing the dry reagents 

 are all connected with each other 

 and with the receptacle for the 

 nitrogen by fusing the ends to- 

 gether. 



The arrangement of apparatus 

 for filling the manometers is 

 shown in Figure 26. The method 

 of filling, because of its complexity 

 and the difficulty of some of its parts, will be 

 described in considerable detail. 



A is the reservoir in which the purified 

 nitrogen is stored up, and from which the 

 manometers are filled. The unlettered stop- 

 cock at the top is that through which the 

 gas, after purification, enters the reservoir. 

 B is the calibrated and thoroughly cleansed 

 manometer which is to be filled and closed, 

 and C is an arrangement for filling and 

 emptjdng the manometer. B is joined to 

 A, at d, by fusing together the ends of the 

 glass tubes; and to C, at E, by means of 

 rubber tubing. The mercury in C is sep- 

 arated from that in the manometer by the 

 air which nearly fills the wide tube below E. 

 In this way, the mercury in C, which may 

 be impure from its contact with rubber tub- 

 ing, is prevented from entering the manom- 

 eter and contaminating the very pure mer- 

 cury with which that instrument is filled. 

 This air also plays an important role when 

 the manometer is closed. 



Before joining the manometer B to A 

 and C, its lower end is immersed in pure 

 mercury and, with the instrument in an 

 inclined position, gentle suction is applied 

 until the two bulbs are filled as nearly as 

 may be with mercury. Owing to the presence of one or more traps, 

 some air will be left in the bulbs, and this must be expelled by 

 bringing the instrument into the vertical position and forcing the 



Fig. 26. — Arrangement for filling 

 manometers with nitrogen. 

 Nitrogen reservoir; (B) cali- 



(A) 



brated manometer; (C) air cham- 

 ber to separate mercury in (i) 

 from pure mercury in manometer ; 

 (E) connector between (B) and 

 (C); (0 and (t) mercury reser- 

 voirs; (k) and (h) two-way stop- 

 cocks; (/) and (g) vents. 



