905 



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

 colourless body, formed by the union of the sulphuretted hydrogen or 

 other substances with the colouring matter of the liquid. This view 

 is chiefly supported by Kane, who says, ' that precisely as the colour- 

 ing matters combine with water, to form different shades of red- 

 coloured bodies — with ammonia, to produce a series of bodies, which 

 are blue and purple — so they combine with sulphuretted hydrogen, to 

 form colourless compounds in solution, which, if solid, would very 

 probably be white.' He supposes, in a word, that for every coloured 

 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 colourless bodies, to which he gave the respective names 

 of leuco-htmine and leuco-orceine." 



The author then gave a short summary of Dr. Westring's experi- 

 ments 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 colouring matter was easily extractable by cold 

 water alone. 



2. Those which required, for the elimination of their colouring 

 matter, maceration in tepid water {i. e., below 25° Swedish thermo- 

 meter). 



3. Those which required maceration in warm water {i. e., between 

 50° and 60° Swedish thermometer). 



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

 " It must be admitted that our knowledge of the true nature of the 



colorific and colouring principles of the lichens is as yet very imper- 

 fect and confused ; and one great cause of the dubiety 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, Roccella tincloria, 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 ; 

 K.a.ne, erythriline : Schuuck,hiseri/thricacid; 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 pro- 

 perties (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 

 VOL. IV. 5 z 



