The hydrocarbon chain of oleic acid is not a saturated one. It contains
a double bond. With a limited amount of oil on the surface of the water
the double bond as well as the carboxyl group may be drawn down onto
the surface of the water. In this way it covers a larger surface area of
the water.
Unsaturated fatty acids cover a larger surface area than satu-
rated ones. Langmuir has measured the length of the molecules and the
area of the water covered by them. He reports that the area covered by the
three saturated acids, palmitic, stearic, and creotic, is practically the same,
yet the number of carbons in palmitic is 16 and in creotic 26, the latter
having the longer molecule. The glyceride tristearin covers an area three
times that of one molecule of stearic acid. From this it is seen that the area,
covered is the same whether as an acid or as an ester of a glyceride. In
measuring the height above the surface of the water he found it to be
the same as the length of the hydrocarbon chains, showing that they are
packed vertically side by side. The results are probably best told in his
564 FATS AND OILS
words. "The unsaturated fatty acids all cover much greater areas per
molecule than the saturated. The double bond in oleic acid is thus appar-
ently drawn down onto the water surface. It is interesting to note, however,
that linoleic acid with its two double bonds, does not cover any greater
area per molecule than oleic acid. It may be that the double bonds attract
one another to some extent in place of the water. Linolenic acid, however,
with three double bonds, covers a considerably greater area than oleic or
linoleic. As the number of double bonds increases, the energy consumed
in compressing the film decreases, probably because the carboxyl groups
tend to be attracted by the double bonds in adjacent molecules and are
thus more easily separated from the water surface."
Polar groups of molecules and water are attracted to each other. Harkins
and co-workers have reported that, if an organic liquid contains polar
groups in its molecules, these groups turn towards the water, and the
amount of work required to separate it from the surface of the water is
greater than when the polar groups are absent. These polar groups are
substances containing oxygen, nitrogen, sulfur, iodine, bromine, chlorine,
or double or triple bonds.
In a later paper Harkins and Cheng have reported that a paraffin with
a triple bond increases the adhesional work very decidedly; they state:
''This and other studies in this paper should prove of value in study of
lubrication and other adhesional phenomena."
Wilson and Barnard have reported that a good lubricant is one that
has the property of "oiliness." They define oiliness as "The property by
virtue of which one fluid gives lower coefficients of friction (generally at
slow speeds or high loads) than another fluid of the same viscosity."
Page 449
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The hydrocarbon chain of oleic acid is not a saturated one. It contains
a double bond. With a limited amount of oil on the surface of the water
the double bond as well as the carboxyl group may be drawn down onto
the surface of the water. In this way it covers a larger surface area of
the water.
Unsaturated fatty acids cover a larger surface area than satu-
rated ones. Langmuir has measured the length of the molecules and the
area of the water covered by them. He reports that the area covered by the
three saturated acids, palmitic, stearic, and creotic, is practically the same,
yet the number of carbons in palmitic is 16 and in creotic 26, the latter
having the longer molecule. The glyceride tristearin covers an area three
times that of one molecule of stearic acid. From this it is seen that the area,
covered is the same whether as an acid or as an ester of a glyceride. In
measuring the height above the surface of the water he found it to be
the same as the length of the hydrocarbon chains, showing that they are
packed vertically side by side. The results are probably best told in his
564 FATS AND OILS
words. "The unsaturated fatty acids all cover much greater areas per
molecule than the saturated. The double bond in oleic acid is thus appar-
ently drawn down onto the water surface. It is interesting to note, however,
that linoleic acid with its two double bonds, does not cover any greater
area per molecule than oleic acid. It may be that the double bonds attract
one another to some extent in place of the water. Linolenic acid, however,
with three double bonds, covers a considerably greater area than oleic or
linoleic. As the number of double bonds increases, the energy consumed
in compressing the film decreases, probably because the carboxyl groups
tend to be attracted by the double bonds in adjacent molecules and are
thus more easily separated from the water surface."
Polar groups of molecules and water are attracted to each other. Harkins
and co-workers have reported that, if an organic liquid contains polar
groups in its molecules, these groups turn towards the water, and the
amount of work required to separate it from the surface of the water is
greater than when the polar groups are absent. These polar groups are
substances containing oxygen, nitrogen, sulfur, iodine, bromine, chlorine,
or double or triple bonds.
In a later paper Harkins and Cheng have reported that a paraffin with
a triple bond increases the adhesional work very decidedly; they state:
''This and other studies in this paper should prove of value in study of
lubrication and other adhesional phenomena."
Wilson and Barnard have reported that a good lubricant is one that
has the property of "oiliness." They define oiliness as "The property by
virtue of which one fluid gives lower coefficients of friction (generally at
slow speeds or high loads) than another fluid of the same viscosity."