THE INHIBITION OF FOAMING The troublesome foaming encountered

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					                    THE       INHIBITION                 OF FOAMING.
                                 BY CYRUS           H.   FISKE.
    (From   the Biochemical       Laboratory       of Western     Reserve   Medical   School,

                     (Received     ior   publication,      May    28, 1918.)

   The troublesome foaming encountered when air is blown
through solutions containing proteins, soaps, etc., or when such
solutions are subjected to low pressures, must be dealt with in
many    analytical and other operations now in use in biochemical
laboratories. Since the most effective agents for preventing this

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foaming (i.e. for accelerating the rupture of the bubbles) are not
now readily accessibleto many who have occasion to use them,
an attempt has been made, in this paper, to outline briefly the
manner of action of such agents, and to determine their essential
properties. From the information thus obtained, it has been
possible to find an efficient foam inhibitor, which can be prepared
with ease from available materials.
   It can readily be shown that this foaming cannot be adequately
prevented by an organic liquid which is completely dissolved.
The presence of undissolved particles of the liquid must therefore
be regarded as essential.’ Something may be learned of the
fact,ors involved in the inhibition of foaming from the behavior
of drops of various liquids upon a clean water surface, a matter
which has been investigated especially by Hardy.2
   When a soap bubble comes int,o contact with a drop of such a
liquid as isoamyl alcohol, under the proper conditions, a film of
     1 Hence      the importance       (e.g. in the m-ease method)         of increasing       the
number        of such particles     by thoroughly      shaking   the mixture      after adding
the inhibiting        agent,    and before starting     the air current.
     * Hardy,       W. B., Proc.      Roy. Sot.,     Series A, 1912, lxxxvi,          610; 1913,
lxxxviii,      303, 313.     See also Pockels,      A., PhUsik.     Z., 1916, xvii,      142; ab-
stracted       in Chem. Abst., 1917, xi, 2067.         Rayleigh,    Phil. Mag.,      1918, xxxv,
412                             Inhibition            of Foaming

the liquid may be seen beginning to spread over t,he surface of
the bubble, and the bubble presently bursts.        A region of dimin-
ished surface tension is produced beyond the visible edge of the
spreading drop of isoamyl alcohol.        The rupture of the bubble
may be accounted for by the existence of two forces, opposite in
sense, acting upon this region at the periphery of the drop; viz.,
(1) the tension of the uncontaminated      part of the soap film itself,
directed outwards,    and (2) the tension of the double surface,
acting inwards.     The rapidity of rupture must depend upon the

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magnitudes of these two forces, among other factors, and should
be greater, other things being equal, the greater the tension of the
double surface, and the greater the decrease in surface tension
beyond the edge of the drop, which depends not only upon the
surface activity of the liquid, but also upon its volatility.4p5
   The chief properties which contribute to the efficiency of an
organic liquid as a foam inhibitor may, from the above discussion,
be enumerated as follows: high surface activity,           high surface
tension, high interfacial tension, low solubility,      low volatility.6
The conditions imposed are not so complex as they may at first
sight appear, since they are to a certain extent dependent upon the
same fundamental       properties.    Solubility  and volatility,      for
example, are, within limits, inversely related to interfacial tension.’
Further, among related substances, solubility and surface activity
are inversely related.8* g*lo
   The surface tension data available73 l1 apply, for the most part,
     3 I.e., the tension           of the alcohol-air        surface,    plus that of the interface
between       alcohol       and soap solution.
     4 Hardy,      Proc. Roy. Sot., Series A, 1913, Ixxxviii,                      315-316.
     5 No account          has been taken here of the adsorption                   of colloidal  material
by dispersed           particles       of the organic       liquid,    since this is apparently           of
secondary        importance.
     6 This statement            is true, of course,       only within       limits;    e.g., an appreci-
able degree of solubility                is necessary.
     7 Harkins,       W. D., Brown,             F. E., and Davies,         E. C. H., J. Am. Chem.
Sot., 1917, xxxix,            354.     Harkins,      W. D., Davies,        E. C. H., and Clark,           G.
L., ibid.,       541.
     8 Traube,      J., Ber. them. Ges., 1884, xvii,                2294; 1909, xlii, 86; Arch.         gee.
Physiol.,       1904, cv, 541.
    *$ Worley,      R. P., J. Chem. Sot., 1914, cv, 260, 273.
   lo Tinker,       F., Phil. Msg.,           1916, xxxii,     295.
    I1 Langmuir,         I., J. Am. Chem. Sot., 1917, xxxix,                1892.
                                                   C. H. Fiske                                                                413
only to pure organic liquids and t’heir pure aqueous solutions;
their use for the present purpose should nevertheless    make it
possible to avoid much unnecessary work in preparing and testing
out materials.    Among those substances    for which data exist,
the above conditions are best met by esters of relatively high
molecular weight,.   An efficient foam inhibitor has accordingly
now been found in isoamyl isovalerate (or a mixture of this sub-
stance with isoamyl alcohol).     Two methods of preparing this
reagent are described below.

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                                        Preparation              of the Reagent.
       Firsl Method-To 35 cc. of commercialisovaleric acid add 4 gm. of
 anhydrous           calcium         chloride.           Shake         the mixture           until       it has separated
into two layers               and most of the calcium                            chloride         has dissolved.                  The
 greater      part of the water                  is in this way removed.                         Decant          off t.he upper
 layer,     and transfer           28 cc. of this to an Erlenmeyer                             flask, of about 200 cc.
 ca.pacity,       containing            a few glass beads. . Add 30 cc. of isoamyl                                         alcohol,
 and 1 cc. of concentrated                        sulfuric        acid.        Connect       the flask with                a leflux
 condenser,          and boil for 1 hour                      over a wire gauze.                    Cool,       transfer         to a
 separatory         funnel,       and draw off the lower layer.                             To the upper                layer add
 water,      and shake           the mixture               thoroughly            with     solid       sodium          carbonate
 until     a sample        of the aqueous               layer,       drawn       off through          the stem, is found
 to be alkaline            to phenolphthalein.                        Separate        again,       and remove               the ex-
 cess alkali          by washing             with        water.          After      drawing         off      the final          wash
 water      (which should not be alkaline                          to phenolphthalein),                 filter the residual
 liquid.       The filtrate           is then ready               for use.         It will, however,                keep better
 if dried with calcium                  chloride        and distilled.
       Second Method.---‘**              I31 14 Dissolve            50 gm. of potassium                 dichromate            in 200
 cc. of boiling           water.           Cool under            the tap, with             constant           shaking.            The
 bulk of the dichromate                     will separate             out in small crystals.                    Add 50 cc. of
 isoamyl       alcohol.         While the mixture                    is keptconstantly               agitated          under the
 tap, now add 70 cc. of concentrated                                  sulfuric      acid at such a rate that the
 temperature            of the mixture                does not rise above 30”.                       Let stand             at room
 temperature           over night.               Separate          the two layers,            transferring             the upper
 one to a 500 cc. distilling                  flask.         Add 200 cc. of water,                 and distill         through        a
 water-cooled           condenser            until     all of the ester has come over.                               Neutralize
 t,he distillate          with      sodium          carbonate,            wash with           water,         etc., as in the
 first method.

    I2 Kopp,     H., Ann. Ckem.,       1855, xciv, 297.
    I3 Pierre,    I., and Puchot,       E., Compt.    rend. Acad.,    1869, lxix, 266; Ann.
chim. et phys., 1871, xxii, 344; Ann. Chem., 1870, cliii, 260; 1872, clxiii,               289.
    I4 This second reagent          has the disadvantage,        for certain     purposes,   of
containing       some isovaleraldehyde,         which     can, however,      be removed     by
shaking      with bisulfite  solution.
THE   JOURNAL   OF BIOLOGICAL   CHEMISTRY.        VOL.   XXXV.                                PLATE        1.

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                                             FIG. 1.
                                                                 (Bock   and   Benedict:   Calorimeter.)
THE JOURNAL   OF BIOLOGICAL   CHEMISTRY,       VOL.   XXXV.                                PLATE        2.

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                                           Fra. 2.
                                                              (Book   snd   Benedict:   Calorimeter.)
THE   JOURNAL   OF BIOLOGICAL   CHEMISTRY.          VOL.   XXXV.                                  PLATE   3.

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                                             FIQ.    3.

                                                                   (Book   and   Benedict:   C&rim&w.)

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