489 



authority therefor, and various relative information, " It is highly prohable 

 that when the chemistry of the lichens has heen more fully studied, and the 

 whole subject of their color- educts and products better understood, we shall 

 begin to reduce the present confused muss of complex substances, and find the 

 same principles more extensively diffused through different lichen species." 

 Dr. L. entered somewhat minutely on the chemical reactions of the better 

 known colorific and coloring principles, and their derivatives, so far at least as 

 these throw any light on the production and transmutation of the red or purple 

 colors extracted from what may be termed par excellence, the dye-lichens. After 

 a few remarks on the chemical constitution of orchil and litmus, as given by 

 Kane, Gelis, Pereira, and others, he discussed the subject of decolorisation of 

 weak infusions of orchil and litmus by exclusion of atmospheric air, and by 

 various deoxidising agents, and the different theories as to the causation of this 

 phenomenon. " I have repeatedly had occasion to notice that, when weak in- 

 fusions of these substances are excluded for some time from atmospheric air, in 

 a bottle, with a tightly fitting cork, they gradually lose color, but rapidly re- 

 gain it on re-exposure. It is curious that both orchil and litmus are what are 

 called transient or false colors, i.e., they slowly lose their bloom and tint by long 

 exposure to the atmosphere ; the coloring matter, therefore, appears to be de- 

 colorised both by exposure to, and exclusion from the air, phenomena apparently 

 of very opposite characters. The cause of the latter phenomenon has never, so 

 far as I am aware, been quite satisfactorily explained; but it has been variously 

 supposed to be due : 



1. To the mere negation of oxygen. 



2. To the development, in the liquids, of various substances, capable of 

 exerting a decolorising influence on the coloring matter. 



3. To deoxidation of the coloring matter by substances, which have a great 

 tendency to become oxidised or peroxised ; e.g. hydrogen, in the case of de- 

 colorisation by sulphuretted hydrogen, ' nascent hydrogen, and the protoxides 

 of iron and tin, &c. 



4. To the fixation of an additional amount of hydrogen in a new colorless 

 body, formed by the union of the sulphuretted hydrogen or other substances 

 with the coloring matter of the liquid. This view is chiefly supported by Kane, 

 who says, "that precisely as the coloring matters combine with water, to form 

 different shades of red-colored bodies with ammonia to produce a series 

 of bodies, which are blue and purple so they combined with sulphuretted 

 hydrogen to form colorless compounds in solution, which, if solid, very probably 

 would be white." He supposes, in a word, that for every colored substance 

 existing in orchil and litmus, there is a corresponding white one, producible by 

 the action of sulphuretted hydrogen, &c. ; and, in proof of this theory, he 

 mentions having obtained from Azolitmine and Betaorceine colorless bodies, to 

 which he gave the respective names of Leuco-litmine and Leuco-orceine. 



The author then gave a short summary of Dr. Westring's experiments on the 

 dyeing powers of the Swedish lichens, which he found might be conveniently 

 divided into four classes, according to the degree of heat employed in their 

 maceration, viz. : 



1. Lichens, whose coloring matter was easily extractable by cold water alone. 



2. Those which required for the elimination of their coloring matter, macera- 

 tion in tepid water (i. e. below 258 degs. Swedish thermometer). 



3. Those which required maceration in warm water (i. e. between 50 and 

 60 degs. Swedish thermometer). 



4. Those requiring boiling water alone, or with the aid of solvents. 



" 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 Eocella tinctoria, which 

 has, of all the dye-Lichens, been most frequently selected for analytical in- 

 vestigation, on account of its important product orchil, the discrepancies be- 

 tween the results obtained are very striking. In it Heeren discovered his 

 Erythrine ; Kane his Erythriline ; Schurik his Erythric acid ; and Stenhouse 



