CELLS AND MANOMETER ATTACHMENTS. 



23 



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tube (B) by packing which is compressed between the rings (e, e). 

 form of the rings is such as to force the material 

 of the packing in both of the lateral directions — on 

 the one side toward the manometer, and on the 

 other toward the wall of the brass tube. The com- 

 pression is effected by means of the hollow nut (/) . 

 The brass ring (g), which serves as a "follower," 

 is made of any required length. A rubber tube 

 is slipped over the cone (a) and tied above and be- 

 low the neck of the cell in exactly the same manner 

 as in the apparatus shown in Figure 9. The reason 

 for the concave form of the surfaces between which 

 the packing of the vent (6) is compressed has al- 

 ready been explained. The packing between the 

 rings (e, e) usually consists of alternate 

 disks of leather and thin rubber, one 

 of the rubber disks being placed below 

 the lower ring, i. e., between it and its 

 1 'seat . ' ' The seat and the under side of 

 the lower ring are grooved to prevent 

 too much lateral movement on the part 

 of the rubber between them in the 

 direction of the manometer; otherwise 

 the greater part of the material of this 

 lowest disk would be crowded into the 

 cavity below the ring. All brass sur- 

 faces which are exposed to the liquid con- 

 tents of the cell are plated with nickel, silver, 

 or gold, according to the character of the 

 solutions whose pressure is to be determined. 



The arrangement shown in Figure 10 has 

 two great advantages over that presented 

 in Figure 9. The use of fusible metal is 

 avoided, and, if the right kind of packing is 

 used, it is not necessary at any time to sepa- 

 rate the calibrated end of the manometer 

 from the end entering the cell, since the 

 manometer is always sufficiently released 

 by unscrewing the nut (/) to permit of 

 its easy withdrawal from the tube (B) . 

 It also does away with the plated steel 

 needle (Figure 9,6), which may be 

 corroded if the solution contains an 

 electrolyte. 



In the apparatus seen in Figure 11 

 the cone (Figure 10, a, a,) is dispensed 



The 



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Fig. 12. — Fifth form of complete cell; for 

 use with substances which attack metals. 



(a) Enlarged end of manometer; (b) brass 

 piece fastened to manometer by litharge- 

 glycerine cement; (c) hollow brass nut 

 resting upon (b) ; (d) brass collar; (e) vent 

 for solution; (/) brass cap with packing 

 in bottom. 



