same inaterial as u-ed for the other deteriniiiatioiiz in each ca-e Each dir iiiori of the particular iiiicrodeii.inieter iiie[l for thiq series of dcterniinations repre-eiited a volmne of 0 0031 nil. a t 20” C. The actual deteriiiiiiatioii. by the rapid method nere macle at iooiii teiiiperatuie. that rarigetl iroiii 20” to 25” C The be.t re*iilti n ere obtained n hen the cliffeicwce betn eeii the t n o reading’s amounted to more than teii *calr clivi~ioii. Thi. i5 due to the fact that the effect of any erior 111 reacliiig tlie tli.placetl volume i. then a. mailer percentage of the total T ulunie than would be the ca4e n here a smaller volume i\ di.placetl. If po5qible. therefore. \aiiiple- large enough to tli-plac~a volume of liqiiid corre.polidiiir: to at lea-t ten
divisioiis of the scale ~Iiouldbe taken. I--el‘ul results:. lion.ever, caii he obtained with iiiuch m a l l t ~iaiiiple., a,< t l i c ~ values in Table IT’ $how. 111 the-e caac- thc results of individual deteriiiiriatioii.: are ieeii to x-ary iiiore from thc truc value than do tho>e where a larger voliiiiic. (JF liquid .ic displaced. h t the average value of a ,series of such (1Pteriiiiii:xtioris is. in griieral, quite satisfactory. . I d e froin tlie sinal1 ainount of saiiiple rrqiiircd for tleiicity tleteriiiiiiatioiis by thir method. another arl~.aiii-agelirs iii tlie rapidity by JTliicli the results may 1~ o1)taiiied. -1 siiiglr tlrteriiiiiiatioii may be made in from 3 to 10 iiiiitutes iiicliidiiig can bc iiiatlo all operation.. and a Gerie. Of (l(,t~riiiiiiati~~iis Jritli siiiiilar rapidity.
Relay for Use in Regulatory Circuits’ L . G . Wesson
iii which tlie operatiiig circuit is automaticallj interrupted and in v-Iiicli uiidesirahle sparking is prevented. has been developetl a d used in therinoregulatioii iii this lahoratory for tlie past year. T T Vdry ~ cells only are iiecesqary for operating thc 1 ~ 1 aand y n-ill last for months viithout attelltion. &ice current i- drawn from the cells only during tlie time that tlie relay ariii iiior-es froin one position to the other. The sparking that occurs a t the hreak of the circuit in tlieriiioreRulator*. ctc.. which may be used i n connection with this aiid certaiii other forms of relays,, is the cause of iiiuch difficulty iii opera-
A
S c.lectroinagiietic rela
Figure 1-Electromagnetic Relay
tioii because of the corrosion or sticking of tlie iiietal tips O K osidation of the mercury surface of the thermoregulator. 111 the relay to be described this difficulty is a\-oitled, since the actual break of the circuit takes place a t ai1 insensitive juiiction in the relay, iiistead of at a sensitive junction in the t hermoregulator. The relatively heavy currents that often are sn-itched oii aiid off by a relay are a troublesome feature of regulatory circuits becaure of sparking. This difficulty is avoided. as -pes of regulatory circuits hrought out in by the-use of a mercury switch2 iii coliiiectioii with this relay. By iiieaiis of this switch currents as 1
1 Received October 21, 1929. 2 This switch consists of a closed glass t u b e into which are sealed con^ tacts of special material. It contains a quantity of mercury which, when the t n h e is tilted, will make or break t h e circuit. With t h e mercury switch there is no open arcing. oxidation, or corrosion. T h e switch contains inert gases hermetically sealed within t h e t u b e which stifle the arc. Different types of mercury switches are available, and are designed t o carry loads from
Description of Relay
The relay (Figure I ) c o i i r i - t i esxeiitially of t w J electroiiiag.iiet~,:~ .\I, M’>eacli acting on m e elid of ail approsiinatelp balanced ami. .-I, .I (wrying a inercury switch, A‘. T\vo wires, TT7, lf7’, which are iiisulatetl From the arm aiid which are provided with platiiium tips, are so arranged that tliq- can he lo~veretlby iiieaiis e ~ s R. , R’. into cups of iiiercury.? F . F’, one of n-hicli is IF101~-each elid of tlie a n n . (-4 layer i d liquid petrolatuin protects the mer(wry h i i i corrosion.) =Idjustnient ( ~ fthe wires is iiiade s o that ~ ~ h i l e the wire a t oiie eiid of the arin dips well iiito the iiiercury when the corrcspoiidiiig elid of the arm is dowii, it just, clear* the surface oi the inerciiry when that end of tlie arm is in tlie raised positioii. The curreiit fro111 tlie dry cells passes through tlie v-ire 11-liicli is in contact with the iiiercury a.3 so011 as the cirruit is closed a t t l i e s e n s i t i v e j u i i c t ~ i o nof the thermoregulator, arid passes thence througli a n electromagnet, at tlie o t h e r elid of the ami. The magnet pulls down that elid of the ariii, -1 and while doing so lifts the wire from the mercury a t the eiid .-l of the ami. and thus breaks tlie cirFigure 2-Toluene Type cuit. -1s the relay starids iion, the of Thermoregulator circuit is closed through the wire, Ti-’, aiid the correspoiidiiig electrciiiiagiirt, .V,rxcept ~ I tlie open junction i n the therinoregulatc,r. Wheii this open jiuiction of the therinoregulator i,? closed hy change of teiiiI ,
I ,
1 t o 10 amperes a t 110 roltij or 1 t o $5 amperes a t 220 volts. hlercury switches are sAd b y t h e Llercoid Corp , 564 \Vest Adami S t . . Chicago. Ill. 3 Sounder magnet4, ruhher-covered. 4 ohms, Catalog 30, 1-0. 6203, J . H. Bunnell 8: Co , 32 Park Place, S e w I-ork, S . I’.
X
AVA L Y TICAL E DI T I O S
180
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, T y p e Q-10 or Type 4010, Minneapolis-Honeywell H e a t 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 b a t h s 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 a n d Stahler, Ber., 42, 2686 (1909). (2) Cain, J. IND. ENG.CHEM.,3, 476 (1911). (3) F r a r y , 2. Eleklrochem., 13, 308 (1907). (4) Smith, J . A m . Chem. Soc., 26, 883 (1903).
