Chemistry. - "The Deterrnination of the Size oflnvisible Parti­cles in Ernulsoid Sols". By Prof. H. R. KRUYT and H. J. C. TENDEJ,OO.

(Communicated at the meeting of March 29, 1924).

1. In a number of communications from this laboratory the theory has been developed ') on Ihe ground of investigations made on sol~

of agar 1), rubber S), starch I),. and gelatine 4), that emulsoid sols are systems in which Ihe dispel'se phase consists of polymolecular par­ticles '); these systems should, accordingly, not be considel'ed as genuine solutions of large molecules.

This theory rested on the observed fact tllat the charge of the partieles in these systems is of a rapillary-electrical nature, which could be established by investigations on the influence of electrolytes in very small concentration on the visrosity of the sols. The theory concerning Ihe J'elation between the size of the particies and the viscosity on olie side (EINSTEIN) 7) and that bel ween the increase of the viscosily in consequence of Ihe elecll"Ïcal charge of Ihe parlieles on the other side (VON SMOLUCHOWSKI) 8) bas shown us Ihe way in this respect. According to the view advocated by lIS the emulsoid sol is a hydrated suspensoid sol, in which the stabilil,y of the sol is governed both by electl'ical charge and hydration.

The reseal'ches 011 Ihe infillence of tannins on Ihe behaviollr of different emulsoid sols U) have givell a new support 10 Ihis theory.

J) H. R. KRUYT and H. G. DE JONG, Zeitschl-. f. physik. Chemie. 100, 250 (1922); cf. H. G. DE JONG, Diss. Utrecht 1921.

') H. R. KRUYT and W. A. N. EGGINK, These Proc. Vol. XXVI, p. 4,3. W. A. N. EGGINK, Rec. tray. chim. 42, 317 (1923).

S) H. G. BUNGENBERG DE JONG, Rec. tray. chim. 48, 189 (1924). ') H. G. BUNGENBERG DE JONG, Rec. tray. chim. 48, 35 (1924). ') Cf. H. R. KRUYT, Koll. Zeitschr. 81, 338 (1922). 6) An investigation on the casein sol has been performed by Mr. H. LIER and

will shortly be published. The results are in perfecl harmony with the theory. 7) A. EINSTEIN, Ann. der Physik 19, 2H9 (1906); 84, 591 (1911). 8) M. VON SMOLUCHOWSKI, Koll. Zeitschr. 18, 190 (1916). 9) H. G. RUNGENBERG DE JONG, Rec. tray. chim. 42,437 (1923);48, 189(1924.).

25 Proceedings Royal Acad. Amsterdam. Vol. XXVII.

378

It l'emained, howevel', de3il'able 10 asrel'taiJl IlOw large the particles ill an emulsoid sol ,'eally are. A direct detel'mination is excluded, tlle sol being amicl'Oscopiral; in the ultra micl'Oseope ollly a TYNDALL cone is seen, A differentiated image, illdeed, arises when a debydmtant is added to the sol, alld it seemed at first as if in tliis way exelu­sively an illcrease of cOlltrast was brought about, and therefore a cOllnting of Ihe partieles was I'endered possible; conlinued investi­gatioJls have. bowevel', thrown doubt UpOIl the qllestion if, and in how fal', it is possible to brillg about dehydration witbout any agglutination of partieles taking plaee. Therefol'e, it remained desirabIe to find a method in wlriell tbe size of t!Je pal,tides in the emulsoid sol is detel'mined uIIder cireumstances which as little as possible gi ve rise to c!Jallges in the sol.

We think we have sllcceeded in tbis alld in wllat follows we give the l'esult of pl'elimillary measllremellts, made 011 the stareh sol, w bich proved 10 be exceptiollally suitable fOl' the purpose.

~ 2. The relatioll bet ween the \'iscosity of a sol 'l')s and Ihe viscosity of the dispersant. 11D is given, in the rase that partirles are uncharged, by lire following formula of EINSTEIN:

'1') .. = 11. (1 + ~ cp ) (1)

in whicb cp is the volume of the partieles as fl'llction of the total volume. VON SMOJ.UCHOWSKI has extellded this formula to Ihe case that Ihe particles are charged, thl'Ough the following relat.ion:

11.-1/0 =~ (P [1 + ~ (~D)'J

'11. 2 'tir' 2.7r " (2)

in which w represents tlle specific resistance of the sol, D the constant of dielertricity, r the mdius of tbe particle, whieh we wish to know, and ç the pot.ential difference in the double layer of Ihe pal,ticle. This relation only contailIs the speeific resist.anee, the pot.ential differenre of the double layer, rp tlle volume of the joint parlicles, and the viseosities whieh ean be detel'lnilled, as was diseussed in earl iel' papel's, Measllrements of the elect.rical condnclivity x in the usual way according to KOHLRAUSCH yield the \"I11ue w; eataphol'etic detel'minations made on the sol, yield the value of the potentialdifference according 10 the eqllation:

4.7r l ;=-'I')u

ED (3)

in which Erepresents the potential difference applied at the elee-

37~

trodes, I the distance of the electrodes and u Ihe cataphorelic velocity of Ihe parlicles.

Rence measUI'ernents of Ihe ('alaphOl'etic velocity 8upply us with Ihe value of the bOllndal'y plane potelltial ç. These rneasuremellis are, howevel', not easy to Cltl'l'y oul; we have applied sllch modi­fications to Ule existing apparatwl that the measUl'ements can be made with an aC(~llracy of about 2 %, Before long we will discus!! Ihis mOl'e al lengtll.

As unknowns Ihere are rlOw left (I' Rnd 1'. When now in an emulsoid sol a numbel' of delel'lniJlations are made with diffel'ent electrolyle cOJlcenlralions, a relalioll according to fOl'mula (2) is obtained each time; bence l' ean t\lways be calculated from Iwo delerminations by eliminaling 'I' bet ween the two equalions,

Whell, therefore, a series of detel'minations are made 011 a sol, either wilh the same electrolyle, or with diffel'ent electrolytes, and the viscosity, the speeific cOllduetivity, and the calaplroretic velocily is every lime measuI'ed, values for r can be calclliated by combining the l'esults in couples.

In tlris Ihe supposition is, however, made that (fJ and l' themseh'es do nol vary with tlre charge of Ihe sol, which is cOlltinually modi­fied by Ule addition of electrolyte.

Eal'lier invesligations have already given supp~rt to Ihe supposition that this is really the case in sols of agal,l) and starch I), which is deeidedly nol a priol'i certain for a sol of gelatine I). The follow­ing results must point out, whether the different combinalions yield constant values both for rand for 'fJ or not.

§ 3. The sllhjoined table 1. containR the vallles for the viscosity, the specific condllctivity, and the cataphoretic \lelocity for a number of 1/, perc. sols of starch, to which several elecll'olytes are added in Ihe qliantities given there. In the sixlh column is found recol'ded Ihe values of {; calculated fl'om the measllrements of the cataphoretic velocities.

Table 2 gives Ihe vallles for rand for 'I', calculated by combining the results from the preceding table in couples.

4. It appears from the second table Ihat constant values for q;

and l' actually appear fwm the different combinations given in the tabie, ti. result which confirIlIs Ihe supposition made.

1) cr. footnote I) on p. 377. ') cr. footnote S) on p. 377. I) Cf. footnote ') on p. 377.

25*

380

TABLE 1.

11. "X 10-6 uX 10·cm. lee. ~X 10'

Number. Added electrolyte. ab •. units e.s.u. volt e.s.u. per-

cm.

• 0.5 m.aeq. KCI 0.01036 78.29 3.10 1.56

2 1.0 m.aeq. KCI 0.01023 146.01 3.02 1.21

3 0.5 m.aeq. MgS04 0.01033 66.83 3.85 1.62

.. 0.8 m.aeq. MgS04 0.01028 99.63 3.23 1.33

5 1.0 m.aeq. MgS04 0.01022 111.53 2.65 1.11

6 0.1 m.aeq. 001016 24.54 2.94 0.98 Co(NH)6CI3

1 0.3 m.aeq. 0,01005 51.11 1.92 0.81 Co(NH)6CI3

TABLE 2.

Number of the rp X 102 rin fo'fo' observation used

1 end 2 5.7 1.1

1 and 5 5.8 7.3

3 and 5 5.6 5.4

1 end 3 5.6 6.0

6 and 7 4.8 6.7

3 and 4 4.9 9.1

Of more importance, ho wever, is the l'esllit obtained about the

actual value of 1', which may be put at about 7 fAfA.

The hydrated par'ficles in the emulsoid sol of star'ch have,aceord­ingly, a diameter of about 14 fAIt. Undoubtedly the hy(hated pal'ticles of this dimension must be in\'isible in the Illtl'a-microscope, and only give rise to a diffuse Tyndall-cone. It would be, however', absurd to considel' such a gigalltic particle as a chemical molecule, though kinetically (but then entil'ely formally) it may, of course, be considered as a molecule. Oul' l'esult quite corrobol'ates the view on w hich our former' theor'ies r'ested. For also the par'ticle, when the hydration water is left out of account, is too big to be consider'ed as a molecule.

According to table 2 the total volume of the hydr'ated particles

38J

tp is about 5.5 1/0 of the volume of the sol, which contains 1/,1/0 of stal'ch; if fOl' the lat ter 1.3 is taken as Sp. GI'., the volume of the dry amyl is 0.4 %, Hence the volumes of the dry and the hyd/'ated particle are to eaeh other as 1 : 14. The I'adii are, therefol'e, to each other as 3: 7. \Vhen, therefore, the water of hydl'ation is not taken into account, a particle would l'emain of aradius of 3 f.Lfl,

henee of a diameter of 6 flfl. For this too the same eonsiderations ltl'e "nlid, as were given just now for the hydl'ated particIe,

The reseal'ch is being continued with some other sols.

Utrecht, March 1924. VAN 'T HOFF-Laboratory,