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. unineulated loop atretchecl aoroe. the top ot the oan, OaDplatina
an electrical oircuit. The 40lay 18 oontrolled by
the amount at ",ater in the oan, the lin at the holo in the
bottom and tho lenath ot l~ul.t.d wlra attaohed to the oork
(aee tlg.l~). Tho .... rbal. -d .. orlptlon ~ thi. 4ell, 18 Aomewhat
oomplicated but thl"chanl .. -!. "ail1 unduatOOCl tra;
tla.I ••
. .
Ce) A ke,. rlna 1. plrtl,117 Immer •• d in •• tar,
the two hel .... a ot tho rina beine kept apart b~ • 'lump ot
.a1t or aular below t~ wat •• l~.l. Onl and ot thl ka, rlna
18 41root17 conneoted to an ,110tr10 1 •• 4 While thl other
end hae • plo01 ot Inaulate4 tape round 1t, and round the
ouhldo ot thil, another e1eotr1o lea4 h .wound. Thu8 thi.
•
latter aleotr1.o lead 1. not Sou ,leotr10a1 oontact. W1tf'.l.b.
k., rlna. The •• It O. lUll!' 41'.01 ..... in the watar, ftbue
parmi t.t1q the two en48 ot tbe ke:r n:lla to ocxae tosethe!"
normall7. When. thil bappena, the en4 of the key rina·wbleb
h in direot eleotrioal oontaot w1th OM eleotrical lead,
touch •• the other lead an4 an el,otrical oircuit 18 _de.
Thie doee not ee. to "be aT'.,. e1mple urena_nt a. tbe
•
.. ,
kef r1na muat 'be lNepm4e4 in ·.uch a ..,. that onl7 the l.ower
halt ot it 11 illlDeraed in wat..r ( ... fil.5). . ..
, (f) An orcUnal"1 'r"~ 'bl4.41 18 plaoe4 o~otIlW1"
1n a ama11 box wob a •• _"toh "boz. A ba1"d .tick of rubb.r
prllviCN817 .oake4 for about .WelTe heNr. 1n patrol (Whiob
makea tbe rubber expand) 18 ~dIDI4 'P.iMt the ruor blade
in sucb a wa, .. to keep l' 1n • oone ... pOI1 \1on •. ~. OM ~.
eleotrio lead 11 attaobed to lthl ruol' blade .hile th. otb.r
11 .. neal' U.. Ae the rub"Mpl'ooutraot., " hrouQtl, thl napora1l on
ot the petrol. the l'Uor bla4. ~ .t.ra1&htlM O\l1o an4 oou. into
contaot wUh the .1re lT1D.11oOl.· .. 1D .th. ~, OOIIIPliUna the
•
oll'Q\Ut. Th. 4el&7 1. aont.I'OUad.·1t1' the 41iune. ot:tb. 100.,
rlre fram th. ruor bla4.'t( ... ti,.6) Th •• abotlUrl ......
to14 tha~ In aot.ual praotlo,lt.b1. 41"1'101 .a. no\ .. ,at.lataoto1'7
.. tho •• praTiouelT 4I1or1be4. . 'tfWI
• ftl
lWi t.ab \0 111 Ule4 UDder
ooul at. ot • nftC ot
.hiob ue t.o .,ta1
platn. An onUn&r7 lna14, tb,
plate.. An ~~:'~~;~5g:~a:~;:'i;g~~:ar5 tbe ..
rubber 1'1111', reat1na on When prd.ure
111 appUd to the top tbe'~i~i~~f.~ the ru.bblr aDd.
eacplete. the o1rcuit (,.,
•
. l l . I t.:! "(.
(b) A turth.r dIT10. 4epan4ant on prelwrl aM
tor us. on ra11ft7 11n ..... 4"01'111,4.. It oonal.t. ot a
double strand ot eleotne lea4, &h • . In4e of -.b1oh U'I
un.1naula t.d. One 1"a4 11 longer and 18 twlate4 round. the other
1n a ap1ral eo that. th.re 11 no ·.UotrlOal oonnaotlon b.twec
them. The ull1n.tulate4 en4A ot th' Ueetr10 ]a.de are kept apart
eea11ng "ax Wh11e the ep1r81 »-rt 11 41ppe4 in • m1xture ot relll n
and paraff1n wax, Which eneure. In.ulat1oa. Th1a deY10e 1.
place4 on a ra11way line and when a tr.1n p..... over the par~
of the track eono~rn.d, tha .n.ela grind a".f the ooat ot
res1n and paraftin! oausing .11l0t-r10al oontaot bet •• en the r .. 1n
and wire ( ee. t1g.C).
Chemical Delllt: A emall medioine bot.tle 18 halt fill.d Wi th
sulphurio 8cl A u,..r at cr41nary paper 11 placed OTer
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