A Sensitive Glass Electrode of Durable Form ANGUS E. CAMERON Eastman Kodak Company, Rochester, N. Y.
T
H E fragility of the ordinary bulbular form of glass electrode is a matter of common experience. The electrode described here approaches the ideal combination of low resistance and rugged form. The steps in its construction are outlined in Figure 1. A bulb of fairly heavy wall is blown from 1-cm. diameter Corning 015 lam. This bulb is blown at an angle of 45" to the tube and is atout 2 cm. in diameter. A small needle flame is then directed a inst the bulb near the stem and, when a small spot of glass is the bulb is removed from the flame and sucked in, thus forming a bulb within a bulb, as shown in B . The sucking is best done through a rubber tube in order to observe the formation of the inner bulb. The bulb is allowed to cool somewhat and a spot on the bottom, diametrical1 opposite the top opening, is heated with a tiny gas flame. A &me about 1 cm. long, burning on the end of a drawnout glass capillary, is suitable for this operation. A small bulb is sucked in until it touches the inner bulb and forms a flat membrane. Without further suction, the &me is directed at the center of this membrane until the glass melts through and the hole opens out.
I 4 ... . ..
Et,
-
6
C
FIGURE1
The electrodes are filled with a small amount of buffer to the level indicated by the arrow in C,and a suitable reference electrode is inserted. The electrode is immersed in the unknown solution to the depth indicated by the arrow. Electrodes of this form are very sturdy, but it is obvious that a severe jolt will break them when they are filled with liquid. Because of the form of the sensitive membrane, they are not well adapted to measurements in liquids of high viscosity. Electrodes of this type have been used continually for 6 months in routine measurements, where they have replaced electrodes of the ordinary bulbular form which were broken on the average of once a week.
It has not been found necessary to attempt to anneal these electrodes. Breakage from strain occurs principally in eleckrodes having too thick an outer bulb. Electrodes which are so thin as to lack durability can be eliminated by gently sucking or blowing in them. A membrane which shows any spots of color, or which clicks when blown in, is too thin. The thickness of the inner bulb can be regulated somewhat by the size of the area heated before the bulb is sucked in Dependable electrodes having resistances of from 1 to 10 megohms are easily made.
RECEIYBDJune 17, 1937.
A Buret-Filling Device for Portable Reagent Reservoirs NEIL E. RIGLER Bureau of Plant Industry, U. S . Department of Agriculture, Austin, Texas
T
H E use of compressed air for filling burets with reagents from portable containers is limited to reservoirs of a capacity which requires frequent filling. The device presented has the advantage that it can be adapted to bottles of any size, and the buret can be filled by the use of a small amount of air affected only to a negligible extent by the solution level in the bottle. The diagram shows the construction of the accessory which is used in this laboratory in 20-liter (5-gallon) bottles. The bulb, A , at the bottom of the bottle has a capacity slightly greater than that of the buret, B, and is of a diameter as large as the neck of the bottle will allow; this facilitates a more complete withdrawal of solution from the bottle. It is sealed to a tube, C, of a size which permits the entrance of the delivery tube, D,carrying the solution t o the buret. The valve, E, is made by grinding a glass rod into a seat obtained by sealing 4-mm. tubing to the bulb. The ground portion of the glass rod is broken to a 6-mm. (0.25-inch) length and inserted into the ground seat. The delivery tube is adjusted so that it prevents the valve from rising too far and becoming unseated. The small stopper in the buret and the large one in the bottle should each carry a small opening to permit the passage of air. The side arm of the T-tube, F, immediately above the pressure bulb is bent both towards the bulb and forward to facilitate closing with the thumb when pressure is applied. One squeeze is sufficient t o fill the buret. RECEIVBDAugust 7, 1937.
436
