in
conjunction with the decomposing action of atmospheric oxygen and
water; others are founded on the reaction between colorific
principles of certain of the dye lichens and some of our ordinary
chemical re-agents." The author noticed in particular--

1. Helot's test, }
2. Westring's tests, }qualitative.
3. Stenhouse's test, }
4. " quantitative.

Helot's test consists in digesting the dried and powdered lichen or
a few hours, at a temperature of 130 degs., in a weak solution of
ammonia, sufficiently strong, however, to be tolerably pungent. One
that is fit for the dyer will yield a rich violet red liquor.

Dr. Westring recommended simply macerating three or four drachms of
the lichen in cool spring water, assisting, perhaps, the solvent
action of the water by minute quantities of common salt, nitre,
quicklime, sulphate of copper or iron, or similar re-agents. If
these means failed, after a sufficient length of time had been
allowed for the development of color, he digested a fresh portion of
the pulverised lichen in water, containing small quantities of
sal-ammoniac and quicklime [in the proportion of 25 parts of water,
1-10th lime, and 1-20th sal-ammoniac for every part of lichen], for
a period varying from eight to fourteen days, and by this process,
he says, he never failed to develop all the color which the plant
was capable of yielding.

Dr. Stenhouse, of London, one of our latest and best authorities on
the chemistry of the lichens, adds to an alcoholic infusion of the
lichen, a solution of common bleaching powder (chloride of lime),
whereby, if it contain certain colorific principles capable of
developing, under the joint action of air, water, and ammonia, red
coloring matters, a fugitive but distinct _blood-red color_ will be
exhibited. The amount of this colorific matter may be estimated
quantitatively by noting the quantity of the chloride of lime
solution required to destroy this blood-red color in different
cases: or the same result may be obtained by macerating for a short
period in milk of lime--filtering--precipitating the filtered liquor
by acetic or muriatic acid--collecting this precipitate on a weighed
filter--drying at ordinary temperatures and again weighing.

The author entered into a full analysis of these tests