ANALYTICAL EDITION
March 15, 1943
Operation After calibration, the apparatus is ready for use. The speed of the stirrer is adjusted to such a value that thorough mixing of the bath is assured without undue agitation. The capillary tube containing the material, the melting point of which is to be determined, is attached a t its uppermost end to an Anschutz thermometer of appropriate range. The thermometer and capillary are then inserted in the asbestos stopper previously described, and put into the bath in such a position that both the material being tested and the thermometer graduations within the suspected melting point range are clearly visible, The initial current to be used will depend upon the melting
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point of the substance, as much as 6 amperes being used for the higher temperatures. The tem erature of the bath is raised rapidly to a point approximateyy 30" C. below the supposed melting point of the material, At this point the amperage is reduced to the value required for a temperature rise of 3" per minute. This heating rate is continued until the substance softens. The amperage is then further reduced to the value required for a temperature rise of 0.5" per minute, which rate is maintained until the substance melts.
Literature Cited (1) U. S. P h a r m a c o p o e i a XII, Class I Material, p . 596, 1942
Simplified Cell Unit for Internal Electrolysis ROBERT P. YECK AND 0. C. ZISCHKAU American Smelting and Refining Company, Central Research Laboratory, Barber, N. J.
I
N ORDER t o follow the bismuth content of lead in certain processing operations, i t is necessary to have a rapid, accurate method of determination. The oxychloride and other older methods sacrifice accuracy for speed. The internal electrolysis method described by Clarke, Kooten, and Luke (1) appeared t o hold promise, but because duplication of the apparatus recommended proved difficult, t h e authors constructed a simplified cell unit from laboratory stock parts. This unit provides greater compactness and convenience of operation a t a fraction of the cost of construction. The methods employed were those recommended by Clarke, KOOten, and Luke (1). The design illustrated is assembled entirely from inexpensive stock items. The only section not found in any laboratory stock room is the hard-rubber base plate, which presents no construction difficulties. The air stirrer shown in the illustrations not only is economical, but eliminates a source of accidental error through contamination of the elec-
trolyte during electrolysis, by copper salts from the electric motor. It also permits more compact assembly of the unit. The cell consists of a hard-rubber or similar electrode support with three hard-rubber binding posts connected together on the upper side with a thin copper strip. Other parts of the cellflushing tubes, anodes and shells, and the cathode-are attached to the hard-rubber base, which rests on the rim of a beaker during electrolysis with anodes and cathode suspended from it into the electrolyte. At completion of deposition, the unit is disconnected from the anolyte reservoir by one rubber tube connection, and lifted from the electrolyte with simultaneous flushing of the cathode. The continuance of the e. m. f. prevents resolution. Figure 1 shows details of the anode construction. The flushing tubes serve as the anode cores, and the method by which the anodes are supported by the flushing tubes and rubber tubing above the plate should be noted. The binding posts are attached by tapped holes, but do not continue through to the under side. It is important to have no metals exposed on the under side. This design necessitates bending the cathode stem to avoid a hole through the plate, as shown in Figure 2. Figure 3 shows the relative positions of anodes and cathode and the extension of the cathode position for the introduction of the stirrer through the center. Figure 4 shows the unit on an ordinary ring stand with all parts in place, exactly as it appears in operation. A small hot plate with high-, medium-, and low-temperature adjustments will be found satisfactory for this purpose. One valve, not two, in the previously designed apparatus is used for anode flushing. The plainly visible outlet tubes make this feature practicable.
A . Stock tubing.
0.25 inch in outside diameter
B. Short length of rubber tubing connecting flushing C.
D.
E. F.
E-
G. H.
I.
J.
FIGURE l . AXODECOXSTRUCTION
tubes t o Y-tube, 6 t o 7 cm. long Bindine nosts. 3: one in Center? outer ones 2.5 om. from cgnier, in line; on either side Overflow tubes, same size a s flushing tubes, bent U-shaped, inverted in use. These must turn t o drain in opposite direction from cathode. A drop of anolyte might otherwise accidentally fall on cathode during removal (Figures 2 and 3) Hard-rubber, Bakelite, or similar material plate, 13 cm. lone. 0.7 t n 1.0 cm. thick. 3 cm. wide. Slight variations Ph dimensions are permissible Rubber stoppers with two holes t o accommodate tubing (flushing and overflow tubes), also a very small hole t o permit passage of anode leads Alundum shells covering anodes, Norton Co.'s RA360 2 X 9 cm. These are cut down t o 7-cm. leneth i o fit standard 400-ml. beaker PlGinum cathode, 5.5 cm. long, 3 cm. in diameter, stem bent as shown in Figure 2. Clearance of cathode and anode shells should be a t least 1.5 cm. Cathode must extend beyond edge of hard-rubber base t o permit stirrer operation through center (Figure 3) Anode flushing tubes serving also as core for anode wire winding. They extend close t o bottom of anode shells and upwards through hard-rubber plate t o 1.5 to12.0 cm. above up er surface. Lead wire winding begins a t extreme power end of these tubes and continues upward t o as close as possible t o rubber stopper. Length of tubes will determine clearance of overflow tube from bottom of plate Copper strip, 6.5 X 1.0 cm. ,connecting bases of all binding posts. After insertion should be greased lightly to minimize corrosion
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
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Vol. 15, No. 3
TABLEI. DETERMINATION ~INATION OF BISMUTH
."*,
-Bismuth Bismuth Found mer"@ eleotrolYms Oxychloride 0.083 0.080 0.073 0.071 0.084 0.082 0.036 0.036
sample NO.
0.039 0.087
0.039
0.084
0.136 0.023
0.129
0.022
-
9.20 0.099 0.018 c.019
9.20
0.099
0.018 0.017 0.016
0.016
By aliquoting equivalent of 0.2 gram of sample.
Operation and Care of Cell Unit
As will be seen from Figure 4, a compact series of these units may he easily arranged. The method ( 1 ) stresses the use of the cell for the determination of small amounts of copper and/or bismuth. However, considerably larger amounts mav be safelv handled by" r e d u c i n g the weight of the sample used, either by direct weight or by diluting and aliquoting. The limiting factor is the amount of bismuth which will form a n adherentdeposit. On perforated cathode used, this is approximately 30 mg. Beyond this point d*culty will be experienced in washing and handling because of t h e p o w d e r y
A . Anode lead through small hole in rubber
stopper to outside binding posts. Anqde WITC is high-punty lead of No. 12-16 B. &
s. gage
B . Anode shell C. Fluahing tube aervlng ~8 lead anode wire core D. Relative positions of lower edge of cathode and anode
FIGURE 2
FIGURE 4. CELLUNIT characteristics. By starting electrolysis at from 40" to 50" C. and gradually raising the temperature to 70" C., some slight improvement in adherence may be noted when working in the maximum weight range. Considerable improvement in this respect will occur in the presence of copper, which may be added in known amounts for this purpose, if desired. Washing of the cathode during removal from the electrolyte should be done with generous quantities of water, hut under a minimum of pressure. CAREOF ALUNDUMSHELW( 1 ) . When disassembling, solu-
mersed-in water.- When the apparatus has not been used for several hdurs wires should be washed off with dilute (10 per cent) nitric &id, followed with water, before each electrolysis. As many as 50 determinations may be made with a single winding, if unnecessarv corrosion is avoided. Contacts should he kept
plate will he helpful.
Results A number of comparisons with the oxychloride method are given t o demonstrate the accuracy of the internal electrolysis technique (Table I). These results give ample evidence of the value of the methods of Clarke, Wooten, and Luke (0,as well as the practical aspects of the cell unit described here.
The Stirrer
W FIGUEE 3.
T O P VlEW
Shows clearance ai cathode and anode shells
se well as extension of cathode position to aaoommod+e centrally positioned stirrer. Note looatioh and direction of overf l o r tubes.
Owing to objections to the electric motor stirrer, a n allglass device has been used. It may be made in the laboratory or purchased from laboratory supply houses.
Literature Cited (1) Clarke, Wooten, and Luke. IND.EN&C ~ E MANAL. ., Eo., 8,411 (1936).
