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A new method for determination of flourine by means of the alteration of glass-surface
VOL. 2 (1948)
A NEW
ANALYTICA
METI-IOD
RIEANS
FOR
OF THE
CHInlICA
ACTA
DETERi\ITNATION
ALTT5RATlON
321
OF FLUORINE
BY
OF GL.V33-SURFACE
One ol Lhc most scnsitivc mcthotls for dctccting fluorine is based on its corrosive action; cvcn when corrosion i5 cxtrcmcly light so as to lx invisihlc, it can Ix pcrccivcd by the alteration of the surface tension under the action of sulphuric acid, The latter, being unable to flow freely and to wet the affcctcd surface of tbc glass, appears clividcd into tiny, easily visible drops. According to this observation of I;E*IXENEUISI~* and following the same proccclurc proposed by HAGEN~, a new method for detecting fluorine with the accuracy of 0.5 y in a drop of the solution to be tested has been introduced. DUBNIKOV END TIKHOn~IROV3 reached a grcatcr accuracy (0.2 y of F- in a drop) using, instead of a glass tube. a quartz one, consisting m a U-tube 4-5 mm in diameter, which supported at the end, a glass capillary that could contain a drop of the solution to test. WC have succeeded in increasing the sensitivity of this method by using the following dcvicc: a small portion tither of the substance to test or of its remaining evaporated solution, is put on a standard microscope covcrglass, free from boric acid, which has been previously dipped for two minutes in a chromic acid cleaning misturc (I g K,Cr,O,, IO ml cont. H,SO,) at 50” C. The covgr-glass is then removed and inserted vertically into the slit of a small wood block, in order to let the cscess of the solution drain off. When the content of fluorine is appreciable, the cl_romic misture coating the glass is condensed Immediately, even at room temperature, into one or more small drops, since glass itself possesses no wettability. When the substance has a minimum of F-, the same result can bc obtained heating very gently, with a micro-burner, not the coverglass itself, but the opposite end of a slide, which supports the cover-glass. Neither anions nor cations, cxccpt boric and silicic acids, can interfcrc with this method, which allows the detection of fluorine even in organic compounds or when dissolved in organic solvents. As for concerning the esplanation of the phenomenon, the opinion of DUBNIKOV cspcrimcnts to clctermine the causes AND -~II
2x
p.
327.
C.
32~
CANNERI,
D.
CO%21
VOL.
2
(rg48)
surface, but from changes taking place in the surface layer are caused by chemical reaction of HI; with the surface layer.” The opinion of the above-mentioned writers has been confirmed by our personal remarks which are corroborated by the acquired knowlcclgc about the alteration of glass layer on account of actual chemical reactions. As is well known, the glass surface, usually hydrophilic, becomes hydrophobic by means of some organic dcrivates of silicon as, for it~stancc, dimcthyl-dichloro-silane, which induces the substitution of 01-I superficial groups with CI-I, groups on the glass which has been previously touched with a strong acid. Analogously, the behaviour of Ill;, in the prcscucc of cont. l&SO,, is as follows: Of1 J-f17 SI / ( 01-i 11.F gl,ls% \s, 011 -I- I-IF ( OIL
I-IB
H,SO* I-I,0 -
,sg<; -I- ,, I I,0
gl‘lh~ ‘Xl
F ( F
In this way the affected surface is unable to be wetted by sulphuric acid. In the prcsencc of water, however, the reaction shifts from right to left and the glass returns to its primitive conditions. There is no evidcncc, at least In the scientific literature which we possess, that any interaction has been until now correlated with the corrosive effect and, therefore, with the alteration of the surface tension at the solution-glass interface, and I?- concentration. The study of such a rcIationship has allowed us to elaborate a new method for the determination of fluorine with great accuracy. Since preliminary observation showed that the drop of chromic mixture which forms on the cover-glass, has a convexity that depends on IT- concentration, measures of the contact angle of the drop, at the glass-solution interface, have been made. For this purpose WC have used: a. a microscope cquippcd with mechanical stage and goniomcter cycpiecc; b. a capillary glass tube made of boric acid free materials; c. chromic acid cleaning misture, containing small and csactly known quantities of P; d. standard cover-glass, boric acid free. The procedure is as follows: first the cover-glass is kept 3 min at So” C. in chromic misturc; the former is then removed and wetted with a small drop of the same solution and, finally, it is set on the mechanical stage of the microscope. The values of the contact angle range from zg” to 7z” for the conccntratiou from 0.5 mg to 0.2 mg o/0NaF in the chromic misturc (Fig. 4a). This method, however, is not to be adopted in spite of its scnsitivcss because there are too many factors likely to interfere with the contact angle at the solutionglass iutcrfacc as, for instance: temperature, time allowed for the measure, size of the drop, and cvcn, the method. of dropping it on the cover-glass. Rcfcvcuccs
$L 3a7.
‘VOL.
2 (1948)
DETERMINATION
OF
FLUORINE
323
h greater accuracy has been reached by us, using the so called “captive bubble method” which is but a slightly alteratcd application of Taggot’s apparatus. This method, usually adopted to study flotation in minerals, allows us to find but any variation of the surface tension. DETRRMINhTION
PROCEDURE
A previously uprightly cut capillary Cube, made of boric acid - free glass, I nun in inner and 5 mm in outer diameter, is dipped into a glass vessel containing I;free chromic acid cleaning mixture. When a light pressure has been produced in the capillary, a tiny air bubble appears at the bottom of it, the shape of which shows that there is practically no contact angle (Fig. I). When, however, the chromic acid mixture contains I+, the “captive bubble” appears more or less flattened, according to the F- content (Fig. 2). In spite of the fact that the contact angle depends upon the bubble dimension. it does not vary for a fixed value of I? concentration. The csact value of contact angle is reached immediately, when the solution is at Go” C but after 30’ at room temperature. The capillary, when rinsed with water, returns to its primitive conditions. The apparatus, as illustrated in Fig. 3, is merely an horizontal microscope,
G.
324
CANNERI,
D.
COZ%I
1’OL.
2
(1gjS)
fitted with mcchcukxl stage, which supports, in a horizontal position, ;t vcsscl containing chromic acicl cleaning misture. ‘I’hc faces of this vessel are plane and parallel. Into the solution is clipped a capillary tube, bent at i-i&t angles ancl conncctecl with a similar one, the opposite cncl of which is conncctccl with a small iron vessel, filled with mercury. The inner volume can bc varied by Iriising or lowering the lifting bottom of the vessel, by means of ELmovcablc prcssurc screw; by screwing, an air bubble appears al the cncl of the first capillary. For mcnsuring the contact angle it is ncccssnry to produce nlignmcnt of the goniomctcr cycpiecc cross hair wit11 one ol Lhc two cclgcs of tlic bubble (IGg. 411).
O)Drop
l’lb’.
method
.).
Arl~asllrcrllcllt
b)Coprrv~
Subbb
of LllO contact
nwlhod
:111glc
To obtain the best result it is ncccssary that the cclgc, the angle of which is to be mcxxwccl, sh~~ulcl occiilq’ tllc niixiian pudliun bct\vcctl tlic ililIct :lnrl the 1:q-I?, C2ICCS p. 327.
2 (rg@)
VOL.
I~ETI:RhlINA'I'ION OF
FLUORINE
325
outer vertical wall of the capillary. To avoid the phcnomcnon of “liystcrcsis”, the contact nnglc must hc mcasurcd during tllc dccrcase of bubble volume, produced by gently screwing rather than during its stationary position. ‘II~c rcproducibility of mcasurcmcnts is about f IO. Experimental values arc obtained by mcnsuring the contact an@ of air bubbles produced into a constant volume of chromic acid misturc (H,SO, d. 1.S4 ml IOO. k,Cr,O, g 2.5) containing a constant volume of NnF solution, at different concentrations from g 0.003 to g 2 per litrc. The concentrations of Na.1; have been cxprcsscd noL only in g/l, but also as pF-, i.c., as csponcnt of I;-, as it is shown in Table I. -
-- -
_ _
. _
Cone
. N;tI: 0
005
0
“12
0.0.:
I _JI(11’
g/l
5
rJC'5U 0 *cl 0 20 O..,O 0 so I 2u 2.00
--.---
-.-_-----
--.-_--
-.-
.--.-
--
.-___--
II
_! “0 .-_
--_-_-
__._.__-.-__
Contact nnglc vnlucs, plottccl against corresponding y NaF/ml values y of Nal? give a logarithmic curve, while plotted against pl? they give a practically straight line, as it is shown in Fig. 5. Thcsc values, howcvcr, are suitnhlc for showing only a relationship bctwccn I? concentration and “cnptivc bubble” contact angle, absolute values of which dcpcnd upon the dimension of the capillary and the quality of the glass which is employed. Using a transparent makrial, resistant to chromic acid cleaning misture, and to hydrofluoric acid, the accuracy of this method can reach the value of 0.5 y in a drop of solution, so that it can he considcrcd not only a semimicro-, but actually a micro-method. ‘I’hc csigcncics of the mcthocl rcquil-c :t preliminary adjustment of the capillary and the vessel with a series of cllf’fcrcnt F- containing solutions, including the one to be determined. Usually, smnll quantities of I;- sic dctermincd cithcr by tiic original DE l3o@m's mcthocl, \vhich is based on the colom fading of %r-Alizarin lake, or by one of its various modifications, based on the substitution of %r by Th and Alizarin by other dyes. Thcsc methods do not climinatc the difficulties arising from the prescncc Rcfc~oms
p. 327.
C. CANNERI,
326
D. COZZI
VOL. 2 (Ic#)
55 50 45 40 35 30 25 20 15 10 5 0
020
00
100
140
1.30
220
260 y No F/ml
33 32 31 30 29 28 27202~
of cations cal~ablc of forming stable complcscs with L+ or from tllc prcscncc of anions capnblc of forming complcxcs with %r ant1 Th; such a11 obstacle cithct limits the rncthod to solutions containing only F- or requires a preliminary distillation of l-IF. howcvcr, although it rwluircs a microscope equipped The method WC propox, with mcch;unical slagc and a goniomclcr cyepiccc, is affcctctl only by the prcscncc of boric acid in the glass and in the solution and by silicic acid in the solution to bc tcstcd. Since the espcriments take place in the presence of conccntratcd sulphuric acid, cvcn the most stable anions, like those formed by Zr, can allow the Tvholc contents of Uuorinc to be transformed into HI;, so that this method is suitable for the dctcrmination of fluorine cvcn in lluozirconatcs.
The new mcthotl Lo clctcrmuw I?- IS bnscd on the xltcrntlon of thr glnss surfncc which posscsscs no wcLt.tblliLy wlicn it is tlippctl into chromic acid clcnning mlxturc contaimng I-IF. The drop of chromic mlxturc wh1c11 forms on the glnss surfdcc has n convcslty clcpcndmg upon I?- conccntratlon. RIcnsurcs of the contact angle not clircctly of this drop but of nn nlr bubble (cnptivc bubble) cl~ppcd into the test solution, arc which nppcnrs at a boltom of a glass Lube. prcwously cnrricd out. Appropriate clcviccs allow cvcn the mirrodctcrm~nation of fluorine. 33orx ncld and silicic ncicl arc the only rcdgcnts ahlc tb affect the axurncy of this mctliotl.
*
VOL.
2
(1948)
DETERhlINATION
OF
FLUORINE
327
ficntion clc la surbcc du vcrrc qui n’cst plus mouillablc tlc\s qu’on l’lmmcrgc clans un mblnngc dc Lichromatc dc potassium ct d’xidc sulfuriquc contcnnnt r-. 1~ gOUtb du m6langc cllromiquc qul SC formc h In surfrxc du vcrrc n unc convcxitL= qui d6pcncl clc In concentration cn fluor. On a pris dcs mcsurcs dc l’nnglc dc contact non pas cx;iCtcmcnt dc 1.1 gouttc mnis dc ln bulk d’air (bullc cnptlvc) qui SC formc ZLl’cxtrbmltt inf6ricurc d’un tube cn vcrrc lmmcrgO d’avancc cl,rns In solution h cx;lmlncr. On pcut m6mc drrivcr Zltics microtl6tcrminntions clu fluor. L’ncdc borlquc et l’ncidc siliriquc sont lcs sculs corps c1u1 pulsscnt dlminucr l’cxactituclc clc ccttc mGLliodc.
Dlc ncuc hlcthoclc clcr F-13cstImmung bcruht nuf dcr Vcrrrnclcrung clncr Gln~ohcrflril hc. d~c kcrnc 13cnctzb.ulcclt bcsltzt, x\cnn QIC in Cllromsilurcrclnlgungsgcm~scll, dxs I-II; cnthdt, gctducllt wlrcl. dcr such nn clcr Glnsobcrfluchc bilclct. lint cinc KonDcr Tropfcn Chromsiiurcgcmisch, vcxitat, cl112von dcr F-Iionzcntrutlon nbhangt. Rlcssungcn dcs Kontoktwinkcls wcrdcn nlcht tlirckt bci cllcscm Tropfcn. sonrlcrn bci cincr Luftblnsc (cnptlvc bubble). cl~c sich .Lm Boclcn wncs Glnsrohrchcns, da5 vorhcr in tlic UntcrGccignctc Vorrichtungcn gcstatsu~liungsld4ung cingct:lucht wortlcu war, biltlct, nusgcfuhrt. ten .sognr clic Rflltrobcstlmmung von Fluor. Uorsrrurc untl Kwsclsclurc hlud tlic cinzigcn lZcngcnlid, dlc tllc GcnikUI6kcIt dlcscr 3Icthotlc hccinflusscn lconncn.
Rcccivcd,
April
(5th 1948
A NEW
ANALYTICA
METI-IOD
RIEANS
FOR
OF THE
CHInlICA
ACTA
DETERi\ITNATION
ALTT5RATlON
321
OF FLUORINE
BY
OF GL.V33-SURFACE
One ol Lhc most scnsitivc mcthotls for dctccting fluorine is based on its corrosive action; cvcn when corrosion i5 cxtrcmcly light so as to lx invisihlc, it can Ix pcrccivcd by the alteration of the surface tension under the action of sulphuric acid, The latter, being unable to flow freely and to wet the affcctcd surface of tbc glass, appears clividcd into tiny, easily visible drops. According to this observation of I;E*IXENEUISI~* and following the same proccclurc proposed by HAGEN~, a new method for detecting fluorine with the accuracy of 0.5 y in a drop of the solution to be tested has been introduced. DUBNIKOV END TIKHOn~IROV3 reached a grcatcr accuracy (0.2 y of F- in a drop) using, instead of a glass tube. a quartz one, consisting m a U-tube 4-5 mm in diameter, which supported at the end, a glass capillary that could contain a drop of the solution to test. WC have succeeded in increasing the sensitivity of this method by using the following dcvicc: a small portion tither of the substance to test or of its remaining evaporated solution, is put on a standard microscope covcrglass, free from boric acid, which has been previously dipped for two minutes in a chromic acid cleaning misturc (I g K,Cr,O,, IO ml cont. H,SO,) at 50” C. The covgr-glass is then removed and inserted vertically into the slit of a small wood block, in order to let the cscess of the solution drain off. When the content of fluorine is appreciable, the cl_romic misture coating the glass is condensed Immediately, even at room temperature, into one or more small drops, since glass itself possesses no wettability. When the substance has a minimum of F-, the same result can bc obtained heating very gently, with a micro-burner, not the coverglass itself, but the opposite end of a slide, which supports the cover-glass. Neither anions nor cations, cxccpt boric and silicic acids, can interfcrc with this method, which allows the detection of fluorine even in organic compounds or when dissolved in organic solvents. As for concerning the esplanation of the phenomenon, the opinion of DUBNIKOV cspcrimcnts to clctermine the causes AND -~II
2x
p.
327.
C.
32~
CANNERI,
D.
CO%21
VOL.
2
(rg48)
surface, but from changes taking place in the surface layer are caused by chemical reaction of HI; with the surface layer.” The opinion of the above-mentioned writers has been confirmed by our personal remarks which are corroborated by the acquired knowlcclgc about the alteration of glass layer on account of actual chemical reactions. As is well known, the glass surface, usually hydrophilic, becomes hydrophobic by means of some organic dcrivates of silicon as, for it~stancc, dimcthyl-dichloro-silane, which induces the substitution of 01-I superficial groups with CI-I, groups on the glass which has been previously touched with a strong acid. Analogously, the behaviour of Ill;, in the prcscucc of cont. l&SO,, is as follows: Of1 J-f17 SI / ( 01-i 11.F gl,ls% \s, 011 -I- I-IF ( OIL
I-IB
H,SO* I-I,0 -
,sg<; -I- ,, I I,0
gl‘lh~ ‘Xl
F ( F
In this way the affected surface is unable to be wetted by sulphuric acid. In the prcsencc of water, however, the reaction shifts from right to left and the glass returns to its primitive conditions. There is no evidcncc, at least In the scientific literature which we possess, that any interaction has been until now correlated with the corrosive effect and, therefore, with the alteration of the surface tension at the solution-glass interface, and I?- concentration. The study of such a rcIationship has allowed us to elaborate a new method for the determination of fluorine with great accuracy. Since preliminary observation showed that the drop of chromic mixture which forms on the cover-glass, has a convexity that depends on IT- concentration, measures of the contact angle of the drop, at the glass-solution interface, have been made. For this purpose WC have used: a. a microscope cquippcd with mechanical stage and goniomcter cycpiecc; b. a capillary glass tube made of boric acid free materials; c. chromic acid cleaning misture, containing small and csactly known quantities of P; d. standard cover-glass, boric acid free. The procedure is as follows: first the cover-glass is kept 3 min at So” C. in chromic misturc; the former is then removed and wetted with a small drop of the same solution and, finally, it is set on the mechanical stage of the microscope. The values of the contact angle range from zg” to 7z” for the conccntratiou from 0.5 mg to 0.2 mg o/0NaF in the chromic misturc (Fig. 4a). This method, however, is not to be adopted in spite of its scnsitivcss because there are too many factors likely to interfere with the contact angle at the solutionglass iutcrfacc as, for instance: temperature, time allowed for the measure, size of the drop, and cvcn, the method. of dropping it on the cover-glass. Rcfcvcuccs
$L 3a7.
‘VOL.
2 (1948)
DETERMINATION
OF
FLUORINE
323
h greater accuracy has been reached by us, using the so called “captive bubble method” which is but a slightly alteratcd application of Taggot’s apparatus. This method, usually adopted to study flotation in minerals, allows us to find but any variation of the surface tension. DETRRMINhTION
PROCEDURE
A previously uprightly cut capillary Cube, made of boric acid - free glass, I nun in inner and 5 mm in outer diameter, is dipped into a glass vessel containing I;free chromic acid cleaning mixture. When a light pressure has been produced in the capillary, a tiny air bubble appears at the bottom of it, the shape of which shows that there is practically no contact angle (Fig. I). When, however, the chromic acid mixture contains I+, the “captive bubble” appears more or less flattened, according to the F- content (Fig. 2). In spite of the fact that the contact angle depends upon the bubble dimension. it does not vary for a fixed value of I? concentration. The csact value of contact angle is reached immediately, when the solution is at Go” C but after 30’ at room temperature. The capillary, when rinsed with water, returns to its primitive conditions. The apparatus, as illustrated in Fig. 3, is merely an horizontal microscope,
G.
324
CANNERI,
D.
COZ%I
1’OL.
2
(1gjS)
fitted with mcchcukxl stage, which supports, in a horizontal position, ;t vcsscl containing chromic acicl cleaning misture. ‘I’hc faces of this vessel are plane and parallel. Into the solution is clipped a capillary tube, bent at i-i&t angles ancl conncctecl with a similar one, the opposite cncl of which is conncctccl with a small iron vessel, filled with mercury. The inner volume can bc varied by Iriising or lowering the lifting bottom of the vessel, by means of ELmovcablc prcssurc screw; by screwing, an air bubble appears al the cncl of the first capillary. For mcnsuring the contact angle it is ncccssnry to produce nlignmcnt of the goniomctcr cycpiecc cross hair wit11 one ol Lhc two cclgcs of tlic bubble (IGg. 411).
O)Drop
l’lb’.
method
.).
Arl~asllrcrllcllt
b)Coprrv~
Subbb
of LllO contact
nwlhod
:111glc
To obtain the best result it is ncccssary that the cclgc, the angle of which is to be mcxxwccl, sh~~ulcl occiilq’ tllc niixiian pudliun bct\vcctl tlic ililIct :lnrl the 1:q-I?, C2ICCS p. 327.
2 (rg@)
VOL.
I~ETI:RhlINA'I'ION OF
FLUORINE
325
outer vertical wall of the capillary. To avoid the phcnomcnon of “liystcrcsis”, the contact nnglc must hc mcasurcd during tllc dccrcase of bubble volume, produced by gently screwing rather than during its stationary position. ‘II~c rcproducibility of mcasurcmcnts is about f IO. Experimental values arc obtained by mcnsuring the contact an@ of air bubbles produced into a constant volume of chromic acid misturc (H,SO, d. 1.S4 ml IOO. k,Cr,O, g 2.5) containing a constant volume of NnF solution, at different concentrations from g 0.003 to g 2 per litrc. The concentrations of Na.1; have been cxprcsscd noL only in g/l, but also as pF-, i.c., as csponcnt of I;-, as it is shown in Table I. -
-- -
_ _
. _
Cone
. N;tI: 0
005
0
“12
0.0.:
I _JI(11’
g/l
5
rJC'5U 0 *cl 0 20 O..,O 0 so I 2u 2.00
--.---
-.-_-----
--.-_--
-.-
.--.-
--
.-___--
II
_! “0 .-_
--_-_-
__._.__-.-__
Contact nnglc vnlucs, plottccl against corresponding y NaF/ml values y of Nal? give a logarithmic curve, while plotted against pl? they give a practically straight line, as it is shown in Fig. 5. Thcsc values, howcvcr, are suitnhlc for showing only a relationship bctwccn I? concentration and “cnptivc bubble” contact angle, absolute values of which dcpcnd upon the dimension of the capillary and the quality of the glass which is employed. Using a transparent makrial, resistant to chromic acid cleaning misture, and to hydrofluoric acid, the accuracy of this method can reach the value of 0.5 y in a drop of solution, so that it can he considcrcd not only a semimicro-, but actually a micro-method. ‘I’hc csigcncics of the mcthocl rcquil-c :t preliminary adjustment of the capillary and the vessel with a series of cllf’fcrcnt F- containing solutions, including the one to be determined. Usually, smnll quantities of I;- sic dctermincd cithcr by tiic original DE l3o@m's mcthocl, \vhich is based on the colom fading of %r-Alizarin lake, or by one of its various modifications, based on the substitution of %r by Th and Alizarin by other dyes. Thcsc methods do not climinatc the difficulties arising from the prescncc Rcfc~oms
p. 327.
C. CANNERI,
326
D. COZZI
VOL. 2 (Ic#)
55 50 45 40 35 30 25 20 15 10 5 0
020
00
100
140
1.30
220
260 y No F/ml
33 32 31 30 29 28 27202~
of cations cal~ablc of forming stable complcscs with L+ or from tllc prcscncc of anions capnblc of forming complcxcs with %r ant1 Th; such a11 obstacle cithct limits the rncthod to solutions containing only F- or requires a preliminary distillation of l-IF. howcvcr, although it rwluircs a microscope equipped The method WC propox, with mcch;unical slagc and a goniomclcr cyepiccc, is affcctctl only by the prcscncc of boric acid in the glass and in the solution and by silicic acid in the solution to bc tcstcd. Since the espcriments take place in the presence of conccntratcd sulphuric acid, cvcn the most stable anions, like those formed by Zr, can allow the Tvholc contents of Uuorinc to be transformed into HI;, so that this method is suitable for the dctcrmination of fluorine cvcn in lluozirconatcs.
The new mcthotl Lo clctcrmuw I?- IS bnscd on the xltcrntlon of thr glnss surfncc which posscsscs no wcLt.tblliLy wlicn it is tlippctl into chromic acid clcnning mlxturc contaimng I-IF. The drop of chromic mlxturc wh1c11 forms on the glnss surfdcc has n convcslty clcpcndmg upon I?- conccntratlon. RIcnsurcs of the contact angle not clircctly of this drop but of nn nlr bubble (cnptivc bubble) cl~ppcd into the test solution, arc which nppcnrs at a boltom of a glass Lube. prcwously cnrricd out. Appropriate clcviccs allow cvcn the mirrodctcrm~nation of fluorine. 33orx ncld and silicic ncicl arc the only rcdgcnts ahlc tb affect the axurncy of this mctliotl.
*
VOL.
2
(1948)
DETERhlINATION
OF
FLUORINE
327
ficntion clc la surbcc du vcrrc qui n’cst plus mouillablc tlc\s qu’on l’lmmcrgc clans un mblnngc dc Lichromatc dc potassium ct d’xidc sulfuriquc contcnnnt r-. 1~ gOUtb du m6langc cllromiquc qul SC formc h In surfrxc du vcrrc n unc convcxitL= qui d6pcncl clc In concentration cn fluor. On a pris dcs mcsurcs dc l’nnglc dc contact non pas cx;iCtcmcnt dc 1.1 gouttc mnis dc ln bulk d’air (bullc cnptlvc) qui SC formc ZLl’cxtrbmltt inf6ricurc d’un tube cn vcrrc lmmcrgO d’avancc cl,rns In solution h cx;lmlncr. On pcut m6mc drrivcr Zltics microtl6tcrminntions clu fluor. L’ncdc borlquc et l’ncidc siliriquc sont lcs sculs corps c1u1 pulsscnt dlminucr l’cxactituclc clc ccttc mGLliodc.
Dlc ncuc hlcthoclc clcr F-13cstImmung bcruht nuf dcr Vcrrrnclcrung clncr Gln~ohcrflril hc. d~c kcrnc 13cnctzb.ulcclt bcsltzt, x\cnn QIC in Cllromsilurcrclnlgungsgcm~scll, dxs I-II; cnthdt, gctducllt wlrcl. dcr such nn clcr Glnsobcrfluchc bilclct. lint cinc KonDcr Tropfcn Chromsiiurcgcmisch, vcxitat, cl112von dcr F-Iionzcntrutlon nbhangt. Rlcssungcn dcs Kontoktwinkcls wcrdcn nlcht tlirckt bci cllcscm Tropfcn. sonrlcrn bci cincr Luftblnsc (cnptlvc bubble). cl~c sich .Lm Boclcn wncs Glnsrohrchcns, da5 vorhcr in tlic UntcrGccignctc Vorrichtungcn gcstatsu~liungsld4ung cingct:lucht wortlcu war, biltlct, nusgcfuhrt. ten .sognr clic Rflltrobcstlmmung von Fluor. Uorsrrurc untl Kwsclsclurc hlud tlic cinzigcn lZcngcnlid, dlc tllc GcnikUI6kcIt dlcscr 3Icthotlc hccinflusscn lconncn.
Rcccivcd,
April
(5th 1948