AVA L Y TICAL E DI T I O S
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perature, the current passes through the electromagnet, Jf, and pulls down the other end of the arm, A , and in doing so tilts the mercury switch to the opposite position. The arm stays in the position to which it is drawn by the electromagnets by reason of the fact that the shaft on which the arm pivots is placed slightly below the center of gravity of the arm. The position of the arm changes only when the electromagnet a t the other end of the arm becomes activated. The arm moves through an angle of 10 to 12 degrees in passing from one position to the other. A small, loose-fitting plunger, P , surrounded by heavy machine oil, acts as a brake to the motion of the arm, and thus prevents undesirable oscillation.
Yol. 2 ,
KO.2
Thermoregulators Used
two contacts are provided, one for the maximum and one for the minimum limit of the desired range of temperature. The same is true of the possible use of the relay in maintaining constant pressure, depth of liquid, hydrostatic head, volume, etc. Other factors being the same, the accuracy of the control attained with the relay is limited only by the sensitireness of the regulator used in conjunction with it. Figure 2 illustrates a toluene type of regulator that has been used in this laboratory x-ith satisfactory results. Toluene, by contracting or expanding, forces mercury to make alteiiiate contacts Kith wires b, b' that lead to one or the other electromagnet of the relay. The regulator is set by screwing inwards or outwards the metallic plunger, p , which extends into the toluene, thus changing the effective volume of the toluene.
Various types Of thermoregulatorsJ such as the bi*netallic type4 Or the Or expansion may be adapted for use with this relay, the only requisite being that
4 Room thermostats, Type Q-10 or Type 4010, Minneapolis-Honeywell Heat Regulating Co., Minneapolis, hIinn., are a readily available form of bimetallic thermoregulators t h a t are adapted for use with this relay for thermo control of rooms or air baths where extreme accuracy is not essential.
Electrolytic Cell for Use with the Mercury Cathode' .4rthur D. Melaven ALUMINUMRESEARCHLABORATORIES, ALUMINUMCOMPANY OF AMERICA, N E W KENSINGTON, PA.
ARIOUS types of mercury cathode cells have been used for the electrolytic separation of metals, particularly aluminum and magnesium from other common metals. While the mercury cathode method has many advantages, difficulty is experienced in separating the electrolyte from the mercury without resolution of the amalgamated materials. T o avoid this the circuit must be closed a t all times
V
M e r c u r y C a t h o d e Cell
during the separation. Separation is made in the SmithHoward ( 4 ) cell by repeated additions of water prior t o the interruption of the current, but this has the disadvantage t h a t the volume of solution is greatly increased. The cells of Frary (3) and of Alders and Stahler ( 1 ) have the same drawback. Cain (2) has devised a cell from which the electrolyte3can be drawn off with a minimum amount of Bash
* Received
February 15, 1930.
water, but in this case a subsequent-filtration is necessary and there is danger of decomposition of some of the less stable amalgams in the process. I n some work demanding the quantitative separation of iron and aluminum, the electrolytic method was used and the cell illustrated in the diagram was developed to effect a clean and easy separation. The cell consists of a cylindrical glass vessel, A , with a conical base, and fitted with a two-way stopcock, B. One arm of the stopcock is connected to a leveling bulb, C, with a piece of rubber tubing. To the other arm is sealed a piece of glass tubing, D,constricted in the same manner as the ordinary buret tip. E is a piece of platinum gauze or coiled platinum wire serving as the anode, and F a narrow glass tube dipping into the electrolyte and through which air is passed to stir the solution. Agitation may also be performed by a paddle and motor. I n operating the cell the leveling bulb is filled with mercury and the stopcock turned to permit mercury to enter the cell. The cathode surface is adjusted by raising or lowering the leveling bulb to the desired height. Contact t o the source of current is n u d e by a piece of copper wire dipping into the mercury i n the leveling bulb. The solution to be electrolyzed is introduced into the cell and the circuit closed. When the electrolysis is completed, the leveling bulb is lowered until the mercury reaches the upper end of the stopcock bore. The stopcock is then turned through 180 degrees to permit the electrolyte t o drain into a suitable vessel. A closed circuit is maintained a t all times during removal of the mercury, either by having sufficient electrolyte present to cover the anode when the mercury is a t the lowest point or by lowering the anode as the mercury is being removed. The cell lends itself t o easy washing with a minimum amount of wash water. Literature Cited (1) Alders and Stahler, Ber., 42, 2686 (1909). (2) Cain, J. IND. ENG.CHEM.,3, 476 (1911). (3) Frary, 2. Eleklrochem., 13, 308 (1907). (4) Smith, J . A m . Chem. Soc., 26, 883 (1903).
