"It must be admitted that our knowledge of the true nature of the colorofic and coloring principles of the lichens is, as yet, very imperfect and confused, and one great cause of the dubity and obscurity overhanging the subject, is the fact that different analysts have arrived at most opposite results, even in the examination of the same species. For instance, in Rocella tinctoria, which has, of all the dye-Lichens, been most frequently selected for analytical investigation, on account of its important product orchil, the discrepancies between the results obtained are very striking. In it Heeren discovered his Erythrine; Kane his Erythriline; Schunk his Erythric acid; and Stenhouse three different substances in as many varieties of the plant; all of these bodies differing more or less from each other in composition and properties (at least, if we are to assume, as correct, the descriptions given of them by their respective discoverers").

"I have already hinted that there is no ratio between the external and internal color or structure of a lichen, and the kind or amount of coloring matter it will be found to yield. It is exceedingly natural to suppose that such a ratio should exist; but, proceeding for some time on this supposition, I was frequently disappointed in my results—the most showy and brilliantly colored lichens often furnishing the dullest and most worthless colors. For instance, the bright yellow thallus of Parmelia parietina, and the beautiful scarlet apothecia of Scyphophorus cocciferus, instead of producing a rich yellow in the one case, and a deep crimson in the other, yielded, respectively, only dirty greenish-yellow and brownish colors. As a general rule I should almost be inclined to say that the finer the color of the thallus of any given lichen, the more is that lichen to be suspected of poverty in valuable coloring matters; and that, on the other hand, the palest pulverulent or crustaceous species, especially such as are saxicolous, may be expected to yield the most beautiful and valuable pigments (e.g. the Rocellas and Lecanoras). In such circumstances it is necessary to have some test, of easy applicability, of the kind and amount of colorific properties of any lichen, and this fortunately is readily attainable."

The fourth section of the paper was devoted to the consideration of the various tests of colorific power, which have been recommended by different authors. "Of these, the greater number proceed on the principle of developing the coloring matter by some alkali, 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,}
}qualitative.
}
2. Westring's tests,
3. Stenhouse's test,
4. Stenhouse's test,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 and processes—pointing out their respective advantages and disadvantages—and showing their practical value and applications. He stated that he had made use of these, and various other tests, in upwards of 300 experiments, and the one which he employed to the greatest extent, because most uniformly applicable, was Helot's ammonia test. The following combination is that most favorable for the development of the coloring matter of the lichens—viz., the presence

1.Of water as a solvent menstruum.
2.Of atmospheric oxygen.
3.Of ammonia, in the state of vapor or in solution, and
4.Of a moderate degree of heat;

And according as the proportion of these combining elements varies, so do the kind and amount of color educed by them. This combination is the foundation of all the processes for the manufacture of the lichen dyes throughout the world, however different these may appear to be in detail or results.