mine and the substitution of twenty
atoms of this element for the same number of hydrogen atoms.

The oxygenated carotins are colorless substances, while the iodide
crystallizes in beautiful dark-violet prisms, having a coppery red
fluorescence.

=Xanthophyll= is closely related to carotin. It has the molecular formula
C_{40}H_{56}O_{2}. It absorbs 36.55 per cent of oxygen (corresponding to 13
atoms, which would indicate the formation of two OH groups in addition to
the saturation required by the C_{_n_}H_{_2n+2_} formula); and an iodine
addition product having the formula C_{40}H_{56}O_{2}I_{2}, which
crystallizes in dark-violet needles.

Xanthophyll differs markedly from carotin in its solubilities, being
insoluble in petroleum ether and only sparingly soluble in carbon
disulfide. It may be fairly easily reduced to carotin. This transformation
is reversible, and suggests a similarity to the change from haemoglobin to
oxyhaemoglobin, and the reverse, in the blood of animals, as a part of their
respiration process.

=Separation of the Chlorophylls, Carotin, and Xanthophyll.=--These
pigments, which exist together in most plant tissues, may easily be
separated from each other by taking advantage of the differences in their
solubilities, according to the following procedure. Grind up a small
quantity of the fresh tissue (leaves of the stinging nettle furnish a
conveniently large supply of each of these pigments) with fine sand in a
mortar. Cover with acetone, let stand a few moments and then filter on a
Buechner funnel. Pour the filtrate into a separatory funnel, add an equal
volume of ether and two volumes of water. Shake up once and then allow the
ether layer to separate; the pigments will be in this layer. Drain off the
water-acetone layer. Now to the etherial solution, add about half its
volume of a concentrated solution of potassium hydroxide in methyl alcohol.
Shake well and allow to stand until the mixture becomes permanently green.
Now add an equal volume of water and a little more ether, until the mixture
separates sharply into two layers. The chlorophylls will now be in the
lower dilute alcohol layer, and the carotinoids in the upper ether, and may
be separated by draining of each layer separately. To separate the carotin
from xanthophyll place the ether solution in a small open dish and
evaporate to a small volume. Now add about ten volumes of petroleum spirit
and an equal volume of methyl alcohol, stir up we