INDUSTRIAL AND ENGINEERING CHEMISTRY
346
Storage of Water Samples
Since the apparatus was not adapted for use on board ship, it was necessary to store the water samples taken a t sea in such a way as to prevent interchange of gas between the water and the atmosphere. It is impossible to keep samples in the ordinary type of citrate bottle, tightly clamped with no cushion of air over the water, without a large percentage of breakage. This difficulty was completely overcome by the device shown in Figure 2, which consists of a U-tube partially filled with mercury and inserted in a citrate bottle completely filled with water. Expansion and contraction merely move the mercury column, and although water may escape outward past the mercury none passes the other way. When inserting the tube care must be taken that water completely fills the short arm and that no air is trapped by the stopper. Samples are stored in a refrigerator until analyzed, especially the deeper, colder samples, which may become supersaturated a t higher tempera tures. Analyses
To show the results of the application of the method to actual sea water some analyses are given in Table IV. These samples are from various depths a t two different stations in
VOL. 9, NO. 7
TABLEIV. ANALYSESOF SEAWATER -Station Depth Meters 0 10 40 60 80 100 150 200
300 400 500 600 800 1000 1200 1500 2000 3000
....
2666Temp.
c.
25 22 14 12 12 12 7 9 7 5 4 4 5 4 4 3 3 2
5 3 5 0
3 9 6 7 2 7 7 2 0 1 6 5 6
...
7 -
Nitrogen lMl./1 9 72 9 50 11.0 11.0 10.8 11.1 11.4 11.7 12.4 12.6 12.7 12.5 12.6 12 5 12.8 12.8 13.0 13.3
....
Depth Meters 10
.... 60 .... .... ..
Station 2667Temp.
Nitrogen
C.
M1./1.
26 0
....
20.9
.... .... ....
8 83
.....
9.67 , . . , .
..... .....
200
18.2
500
ii.3
10.3
800 1000
14.8 11.5
10.4 11.3
5.2
12.6
.... ....
.... ....
1500
.... ....
4000
....
....
.... ....
....
3.1
9.64
..... .....
.....
..... ..... .....
13.9
the Atlantic south of Cape Cod: No. 2666, north of the Gulf Stream; and No. 2667, south of the Gulf Stream. Further studies on the content of dissolved nitrogen in sea water will be reported in a subsequent paper. RECEIVED April 21, 1937. Oceanographic Institution.
Contribution No. 141 from the Woods Hole
An Improved Salt Bridge for Electrometric Measurements WILLARD M. BRIGHT AND ELMER L. MILLER, University of Toledo, Toledo, Ohio
I
N THE course of making electrometric measurements, it
was found that available salt bridges were not entirely satisfactory. At the present time the bridges most recommended are those developed by Irving and Smith (3) by a modification of an earlier type described by La Mer and Baker (4, 6), or of the type devised by Stern (8). Other apparatus of this nature has been introduced by Clark ( I ) , M N e r (7), and Michaelis (6). The chief disadvantage of such siphon bridges has been the necessity of maintaining the same liquid level throughout the system, or using a bridge containing an aqueous gel such as agar saturated with potassium chloride. The former method is inconvenient and the gels are unsatisfactory, as the presence of a foreign porous material a t a junction may be a cause of error (2). Also, it is advantageous to use a free liquid junction in order to ensure a rapid attainment of equilibrium conditions. The bridge shown in the figure is entirely constructed of hardglass tubing with 0.5-cm. bore, except for reservoir B which is
made from the bottom of a 250-mm. Pyrex test tube. The ground-glass plug shown at D, which is used to maintain the liquid column in the tube below it, may be replaced by a short rubber tube and a clamp. In preparing the bridge for use, the reservoir is filled with the chosen salt solution. After closine the stODcock a t A . which is part of the reference electrode vessel, the ;eservoir is ’forced on rubber stopper C. This will fill the bridge to E, with any excess being drawn off through the lower stopcock. The vertical tube is then filled by drawing the salt solution up into it with the stopcock at F open, then closing F while the plug at D is fitted into the tube. An extension tube may be fastened to G to allow any convenient height arrangement of the apparatus as is usual in titrations or pH determinations. This bridge has been used in a number of other ways. The tip of a single electrode vessel may be introduced a t D in place of the plug while the stopcock in the vertical tube is closed, for determination of cell potential. Measurement of concentration cells has also been accomplished with this apparatus. This salt bridge may be left connected in a circuit for a long time, as it provides a very long path for diffusion. It gives a free liquid junction, and may be used a t any height in reference to the liquid levels in the rest of the system. The only precaution to be observed is that connections must be air-tight to prevent siphoning. Literature Cited (1) Clark, W. M., “Determination of Hydrogen Ions,” Baltimore, Williams and Wilkins Co., 1928. (2) Fricke, R., 2. Elektrochem., 30, 577 (1924). (3) Irving, G. W., and Smith, N. R., INDENG.CHEW,Anal. Ed., 6, 480 (1934). (4) La Mer, V. K., and Baker, L. E . , J. Am. Chem. Soc., 44, 1954-64 (1922). (5) LaMer, V. K., and Parsons, T. R., J . Biol. Chem., 57, 613-31 (1923). (6) Michaelis, L., “Praktikum der physikalisohen Chemie,” Berlin, Julius Springer, 1922. (7) Muller, E., 2. Elektrochem., 30,577 (1924). (8) Stern, H. T., J . P h p . Chem., 29, 1583-4 (1925). RECEIVRD M a y 7, 1937.
