as, in which the R represents the whole of the complex
group to which the acid ester groups are united:

COO.CH_{3} COO.CH_{3} COOH
/ / /
R R R
\ \ \
COO.C_{20}H_{39} COO.C_{2}H_{5} COOH

Amorphous chlorophyll Crystalline chlorophyll Chlorophyllin
or or
methyl-phytyl methyl-ethyl
chlorophyllide chlorophyllide

"Chlorophyllin," the compound in which the ester groups have been converted
into free acid groups, as indicated above, may be obtained from either
amorphous or crystalline chlorophyll by treatment with caustic potash
dissolved in methyl alcohol.

=Phytol.=--This alcohol, which furnishes the characteristic ester group in
the chlorophyll of plants, is a compound of very unusual composition, which
has never been found in any other form or in any other type of compound
which is present in either plant or animal tissues. Careful studies of its
addition and oxidation products prove that it has the following structural
arrangement:

H H H H H H H H H H
| | | | | | | | | |
H-C-----C-----C-----C-----C-----C-----C-----C-----C=====C-----C--CH_{2}OH
| | | | | | | | | | |
CH_{3}CH_{3}CH_{3}CH_{3}CH_{3}CH_{3}CH_{3}CH_{3}CH_{3}CH_{3}CH_{3}

As this formula indicates, the compound contains one unsaturated,
double-bond linkage, one primary alcohol group, and eleven methyl groups.
As has been said, this alcohol occurs nowhere else in nature, and its
presence and function in the chlorophyll molecule are, as yet, wholly
unexplainable. Phytol itself is a colorless, oily liquid, with a high
boiling point (145 deg. in vacuo, 204 deg. at 10 mm. pressure).

THE CONSTITUTION OF THE CHLOROPHYLLS

As has been mentioned, chlorophyll _a_ differs from chlorophyll _b_ by
having one more oxygen and two less hydrogen atoms in the molecule, and in
having one of its nitrogen atoms in the "lactam" arrangement. These
differences in structure are represented by the following formulas which
are commonly used to represent the two compounds, but which do not show the
arrangements of the major groups