substance that provides color of milk

Rob Hooft R.Hooft at EuroMail.com
Fri Aug 8 03:11:33 EST 1997


>>>>> "JM" == Jim Mau <elgusano at lapalapa.com> writes:

>>>>> phg (pgueguen at alpes-net.fr) wrote:

 phg> i d like to know witch substance provide the white color of the
 phg> milk?

 JM> 	If I recall my freshman chemistry correctly, Milk is a
 JM> "colloidal suspension" of fat 'micells' (little round fat balls,
 JM> i.e., the 'particles') in the liquid portion (i.e., the solvent).

...and colloidal suspensions of one "optical density" in a solvent of
another "optical density" display so-called ``Rayleigh
scattering''. The efficiency of this scattering in different
directions is wavelength-dependent, but milk contains so many of these
particles that 100% of "red" or "blue" are scattered anyway. For
"skim" milk the number of particles is probably less, resulting in a
slight color difference with normal milk [but in that case you should
see a huge color difference looking through a thin layer of skim milk
towards a light as opposed to looking at it from the light side].

May I remind all of you that if an object has a color X, this is
because it absorbs light of colors that are not contained in
X. Having a white color thus means ``absorbing light of colors not in
white'', or ``not absorbing visible light''. This is hardly called a
color, I would call it "lack of color".

Going back to the question: None of the components in milk have a
color. Milk is white because it contains large particles of different
optical density than the solvent, which ``scatter'' the light.

Another look at it: milk is white for the same reason the sky is blue
and the sun in the evening sky is red (and don't laugh, it is true).

Regards,

Rob Hooft.
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