J. Nordmonn' and Edwln Steinbeg lot Angelet Volley College Van Nup, California 91401
II
A Bridge-Re~tifier-Mihmmeter Instrument for Conductance Studies
I n R previous pnper' we described mnThe low mncluctnncc rsnp;c is mt~dcpnssihle hy com:I 0 to 1 milli:~mlrreclcmrtrr, nnd CK.,&, stnlction of n device for contluctn~tcetlrmonstrntions in hinntion of .I/, 1 r i d g e rectifier. 1.nnip I, is osrd :I..:in o n 4 italirator the frcshmnn I:ilmrntory. l'he prtrlwsc of its drsign wis to rrplnee t h r commonly wrcl yrt clnngerous fullnncl :I mnat:~ntlo:wl (t~lrrdcrcurrrnt) for the srro~d:iry of trnnsformer T. Tot:il pnrts mst, inclrrcling d r c linolmwrr co~ul~~ct:utce circuit which miuses solution trncles und meter, is ntmut S30. henting and yirlclx only sut~jcctivcrrsrtlts frnm the With rvitrh S?oprn thr r o n d ~ ~ c t n ntest. ~ e cell pnswu oprrntnr's estimntion of lnmp l~rilli:ince. \Ve h n w now n~oclilirclthe nppnmtus to mmploy more rendily nvnilnl~lr only the mrtrr circuit currrnt nnd p r n v i d r ~rrndings for s o l ~ ~ t i o nofs lower concl~~ctsncr.1Vitl1 S? ch~scrlthe p:wts : u ~ dto ir~cli~rlr :In ndclitionnl o p e r n t i ~ ~nmgc g for t i i t y S r a r the low-rontlnrtn~~ee nmpc extreme t h r milli:~mmrtcrrrnds 17; of full-sctle clrflrction with comn~rrci:ddistilled wkter h n v i ~ ~:I gspecific rrsistnnce r of 4.5 X 10nnhm cm. To\varrl the l ~ i g l ~ - c o ~ ~ c l r ~ c t a ~ ~ c e dcrnnpe extrrme the meter shows %yoof fi~ll-se;ilc~ flcrtion with 0.75 F HCI for whirl1 r = 4.0 ohm em. (;\I1 work r ~ ~ p n r t chere d wrur done s t 2Z°C unless othcrwise notccl.) Inshument Description Jnstrnd of me:~qIuringwlution rrsiatnnce directly the instr~~mrnt. men.q~~rrut.hr smnll currrnt which pwses I r t w r r ~rlrrtrodrs ~ standing in the wlution. As rhown in 1:iptlrr I it is :I morlilit~rlohmmeter consisting of nn nmmrtrr, c~trrrnt-limitingresistors nnd pnwrr supply.
Flovn I. C i M i t d i a p m n C cadvctan.. cdlr d 2J.Kn 10% resismrt r, 5 K f l potmtiomekrr Rr 100!1 10% 1 W n d r m r t st dnpls pol. single lhmw lrp.rl.l power switchr S: rp.rr. mnge w i t c h ; 1 Mozdo 148 lomp. 6.3 V, 0.15 amp; M 0-1 dc milliommetsr, Welch model 451 or .qulvdsnti 1 p h a . I m k lrlored drwill; CR.M innrumsnt lbridgsl r&iRcr. 5 milliamp moximvm, Cononl t y p e B-C m r i a 160-C or cquivolenlt T stepdown trmrformcr, 115 V primow, 6.3 V se - V ~ 1 1 r1r r r p t : t r I r nr i n t n :I I i ~ wr t * m l l : ~ t n r t ~ ~ n s f n r n i c * r 'I'n~nsfnrmrr , T is grn1111f1rd :III~II:I* :I :nfr m t . p i ~ to f t i 3 V 111 full-lo:~cl r ~ ~ r r r n t I. t r s i s t o r KI w t x :I n ~ i n i m r ~VIIIIIP n ~ of rirruit rrsist:111rr for p ~ ~ ~ t , r r ot if om! r~t w :III~ rrctilirr. I . ' i m r ~ s2. 3, : I I ~ 4 p r n v i c l ~:dditi111~11r n n * t n w l i o ~ ~ f l r t : ~ i l s . O m > t h r l x l r t s :~rr r n l l w t v d :I t : d t t ~ i r i ~wit11 ~n
Figure 2. Wiring diagram Th. r 4 . r is lhom mporohly (Fig, 4 ) order to properly identify ih lhme block leads. The meter h show mparolaly (Fig. 3)to make dear ih wmsclion to lho r&iRer. in
nu;
Fiwrr 5 s h o w thr r l r c t r n d r essrmhly, t 1 w hright p l n t i ~ ~ rwires ~ m s e : ~ l r d in glnss. Thr r;hirlclrcl rnhlt. i s ~ I)? optinnnl. E l r c t r n d r s o f I:lrgc*r:mim:iy I Ipr~p:~rrcl h s n i m r r i n g t h e p1:1tin11m w i r r s R:lt I w f n r r s r d i n ~ ,t h r n nligning thmm w i t h fl:rt sirlrs n111111:111y ~:I~IIIPI Iwktrr 1:1pi11g t o g r t h r r t h r ~ I : w s lx r r v r s for ~ : I ~ I I ~ ( ~ : I I I ~ oPf g r o n w t n . l ' r i o r t o sr:ding :lnd l i ~ mhooku11 l 1,111- w i r r s tw r l r c t r o m : ~ t r c l1vit.h p l : t t i ~ ~ r ~l ~ml : t c k fmm n ~ : ~:dsn y r h l n r n p l : ~ t i n i r :lrid w111tin11 t n n ~ i n i m i z rpnI:~riz:ttiot~ r f f r r t s . l'hr s t i l l p n l y r t h y l r n r r o v r r :lllorcl.; n ~ m r c l p m t r r t i o n sn t h e r l r c t r n c l r :~ssrnml>lycittl l w WPII S I: nrrclrrl t o s t i r snlutions. Opemting Chomcterirtier and Collbmtion
Figvn 3. Front and side view% lh r M i i e r C I is mwnted a en lnn.. ruloting (vrtorl board behind metor M to minimiz. Ieod lmglh bh lhe ho. It i s mdairabte 10 wlder to lhs reeiner lugs since wldering heel con domoge the rsoiRcr. lhe box may be mode of quarter-inch plywood.
C o n d u c t : u ~ c rrrll r u r r r n t v e r i r s w i t . l ~t h r r h n m c t r r o f s o l u t i o ~ lt r i n g mr:~surrcl. I n t h i s i n s t n ~ m r n lconcluct : ~ n r rdl t w l / o ~ r:IIW w i r i r s s i ~ ~ irt r is rq11:11 t o trht~sf o r m e r scconfl:~ryvolt:lgr m i n u s t h r volt:lgc. drnp :wrns< t h e ~ n r t e r i ~circuit-:~nd ~g h h g :I f1111rtion o f ~OII~IICt : l n r r c e l l r u r r r n t , m r t r r i n g r i r c l ~ i tv o l t : ~ g ri.s v x r i : ~ l ~ l r , ('rll volt:lgr w o r ~ l cnpp~nsrll l ron.;t:u~turl l:.\ if t h r mrtfsring circuit r r s i s t : ~ n r r w r r nrgligildr. H c n v r v ~ ~ rin , I ~ i g I ~ - m ~ ~ f l ~ s~ocl ut :t i~nt~~~crsrr,r t i l i f , r :III~ i n r t r r 1111nlout WIIIII~ o r r u r . . i s nnr r c w l t nf t h i s v:iri:inrf> r u r v r s in. d r : l c i o f s t n i g h t l i n r s :~rro h t : l i 1 1 ~ 1ill r o ~ ~ f l l l r l : ~ ~ ~ r r t i t r : ~ t i o up l o t s (b'ig. ti). Si11rr t h e circuit's p r r f o r n i : ~ ~ ~prr r r l ~ t c l r sfindi11g :I s i n i p l r m : ~ t h e m : ~ic:d t r r l : ~ innship t l w t ! v r r ~n~i i l l i : ~ n ~ m r t r r r r : ~ i n g: I s i f i r n ~ ~ l ~ ~ r ti t: ~i s~ nr rrr .r s s : ~ r y t o l w IISWI i n :LIISIIIII~~ r d i t ~ r : ~tthre i ~ ~ s t n ~ tIn~ r ~I ~Ii t~ t r:lnI *
10
YO
30
r m r w r *OLUMI.
10
YI
-I
A double arid-bos. t i t r d i a ef I 0 0 mi of HCI-HOAc mixore 0.355 F KOH. wing Hm high.radwtome rang.. The a d point a t 16.2 ml, rormsponding lo lh. nsvtrolizotia of 0.0575 F HCI, worn conflrmad by lhe indvrion of malhyl ormgc indicamr. The end poinl of 38.4 ml, corresponding to 0 second titrotion increm.nt of 22.2 ml lo nevtrolix. 0.0788 F HOAq r o r c d r m e d by me additim of phen01ph~~l.in indirotor after me R n t a d point r m Milliommetcr readings obove Figure 6.
with
the mel.r's plied by
mwhed limit are cmlculotsd r h m ob*ened reedings ore multi.
..
.
POI rolibretia of me high.omducton
